Philosophy and Philosophers - an Introduction to Western Philosophy - Chapter 2

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CHAPTER TWO

Greek philosophy:

Plato, Aristotle

The period of Greek philosophy that followed the Presocratics begins

around 400 BC; the most important figures are Socrates (470–399 BC),

Plato (427–347 BC), and Aristotle (384–322 BC). It is possible to discern

a shift in interest in Greek philosophy away from explanations of the

natural world to moral concerns, in the sense of discovering the best

way for men to live. The difficulties of determining what were the

objective or real features of the world, as opposed to those only

apparent features which depended on a point of view (and hence were

subjective), began to undermine the early explanations of natural

science. If we are uncertain about what features of the world are real

and what are only apparent, then it is unsurprising that such doubt

will extend to the objectivity of moral standards. The threat was of

moral anarchy.

To understand later Greek philosophy it is necessary to remember

some unsolved problems derived from the Presocratics. In one sense

Heraclitus stands at one extreme, Parmenides at the other. For

Heraclitus everything is in flux; there is no being, only becoming or

processes—although this becoming is subject to a cosmic logos or law

of change. Heraclitus holds a compositional theory of identity

whereby something remains the same thing only if the stuff out of

which it is made remains exactly the same stuff. The world as it

appears to the senses is argued by the Parmenideans to be an illusion:

it is a world that appears to involve change and plurality, but these

are impossible. The world for the Parmenideans is a plenum (full, or

containing no void), and change, movement, plurality and diversity

are impossible because they involve an X becoming a not-X (nonbeing,

or a nothing); but even not-X is something, therefore not-X is

self-contradictory, since it asserts of X both that “It is” and “It is not”.

Thus the appearance of change and plurality presented to us by the

senses is impossible, since it involves a contradiction; it is an illusion.

One answer derives from Democritus and the other atomists; the

21

attempt is made to reconcile the explanation of the empirical world

with the Parmenidean paradoxes; and the answer is to posit atoms

with Parmenidean oneness of being in a void, which lies beyond the

world as it appears. In just the way that Parmenidean arguments

demand, these atoms do not, in themselves, change or have parts, but

the appearance of change and diversity is explained by the coming

together and dissolution of aggregates of atoms combined with the

effect of these changes on us.

There are, however, problems with atomism. First, there is the

difficulty that the atomic world is by definition beyond appearances;

its existence cannot be empirically verified, it can only be posited, and

cannot be known to exist. Second, the properties that the atoms are

supposed to have are said to be objective or real because they are

properties which are independent of observers. On inspection the

suggested properties, such as size, shape, motion, seem to be equally

dependent as properties such as colour and heat on one’s point of

view. Thus X can be large to you, but small to me; X can be fast

moving to you, but slow moving to me; but it would be contradictory

to suppose that X has both properties, and since we have no reason for

choosing one appearance over the other, X cannot really have either of

these properties. No property can be real if its being-what-it-is is

dependent on the point of view or state of the observer in this way.

Third, mere aggregates of atoms, which might be said to make up

some thing (this horse), seem to give no account of the commonsense

or pre-theoretical notion of separate or independent individual kinds:

an independent “this so-and-so”. “This so-and-so” is an independent

or separable individual, uniquely distinguished from any other thing,

and can undergo certain changes while retaining its individuality or

identity as a “so-and-so”. The “so-and-so” of an individual “this” is

spelt out in its essential nature or “whatness”; the essence is those

features which are necessary and sufficient for it to exist as a

determinate kind of “so-and-so”. This reflects the difference between

an individual horse and a mere indeterminate lump of bronze. Without

real or substantial separate individuals there is the suggestion that

when we say something has become an X (“this so-and-so”), it is

purely conventional or relative, and dependent on how our language

happens to chop up the world; in reality no new substance has come

into being at all, there has just been a rearrangement of the only true

substances: the atoms.

These considerations lead to scepticism about our knowledge of

the empirical world. One answer, proposed by the Sophist

Protagoras (c.483–c.414 BC) is to embrace conventionalism or

relativism, and say that reality is not something independent of the

way human beings have come to divide things up through their

thought and language; there is no reality which is the way things are,

independently of the way we talk about it; what we take to be

22 Greek philosophy

relatively stable factors in the world are derived from facts about

how we talk about the world. The danger here to universal ethical

standards is obvious. If what in all cases we count as X and as

ceasing to be an X is merely a matter of conventional fact or relative

to a point of view then it could be thought to be a mere convention,

or relative only to a point of view, whether X is morally good or

right, bad or wrong. There is no longer any matter of objective fact; it

is just a function of the way we happen to talk, it is a relative truth

because our criteria for X, reflected in the meaning of the word for X,

could change. In the case both of empirical and of moral assertions,

we could adopt different conventions; and there would be no

grounds to choose between one or the other derived from pointing to

objective independent constraints in the world or outside our

conventions, for there are none. What seems good, from a certain

point of view, is good, and we cannot say objectively that one view is

more legitimate than another.

Plato

Plato was born into an aristocratic Athenian family. He is, along with

Aristotle, perhaps the most important figure in the history of Western

philosophy. As a man he is difficult to know, although a strong

personality plainly emerges from the many dialogues he wrote.

Although he thought of entering politics, he became finally

disillusioned with it following the execution of Socrates. Plato’s own

philosophical views take Socrates’ views as their starting-point; and

our knowledge of Socrates derives almost entirely from Plato’s

dialogues, in which Socrates is often the main character. Around 380

BC Plato founded the Academy for the propagation of knowledge and

education for the future rulers of Greek city-states. The Academy

would have been unlike a modern university, and more akin to a

college where there would be ritual communal activities, such as

taking meals together. Among the intellectuals of Athens were the

Sophists, or “experts”, who, unlike Socrates, charged for their teaching

services, giving instruction on rhetoric and efficacious behaviour in

public office. Socrates, like Plato, considered Sophist claims to

knowledge ill-founded, and set out to expose this fact; generally

Socrates regarded them as ignorant men who, worst of all, did not

even know they were ignorant. The curriculum of the Academy

included philosophy, mathematics, astronomy, and some natural

science. Later in life, Plato became reluctantly involved in a disastrous

visit to Sicily aimed at educating Dionysius II. Plato perhaps felt the

need to try to put his political philosophy into action. He returned to

Athens, and sheltered from the political storms around him. He died at

the age of eighty years old.

Plato 23

It is against the Presocratic background that the views of Socrates

and Plato emerge, starting with a concern for ethical matters; but the

same overall approach is applied to knowledge generally. Questions

are asked, for example, about what is good or what the good is; for

surely knowledge must be knowledge of what is. We can apply this

by taking the example of justice. Socrates does not simply state an

answer to the question; rather he admits his ignorance and asks his

interlocutors for hypotheses, which start with experience and the

inductive gathering of particular cases as a first step; he then goes on

to test the hypotheses through arguments demonstrating their

consequences, and shows that the answers merely give an example of

the thing he is after, and an example, moreover, that cannot be

justice-in-itself, but is merely justice from certain points of view that

cannot universally be called justice. What he is after is justice-initself

(the Just); justice without qualification or unconditionally. For

it is in virtue of a fixed justice-in-itself that all things, or all cases,

which we correctly call justice are justice. All those things we call

just must share some common and peculiar characteristic in virtue of

which we are correct to call them all just. To act justly, we need to

know what justice truly is. If we talk of X without knowing what X

is, we literally do not know what we are talking about. What

Socrates is seeking is a true or real definition; that is, not merely an

account of how we, in fact, use a word, nor a stipulated use, but a

definition that tells us of the true nature of the object or quality to

which the word applies; that is, its essence. This is similar to asking

for an objective account of what is justice, independent of any points

of view.

To have knowledge of something, X, involves understanding what

we truly mean by the term “X”; and understanding the true meaning

of “X” involves saying what X is—what the essential fixed nature of

X is—what it is for X to be the kind of thing it is. Socrates is

concerned not chiefly with the meaning of the word “X”, but with

the object X, and the real nature of X as determining the true

meaning of “X”.

Plato holds a realist theory of meaning and knowledge. The

meaning of terms and that which we come to know is a process of

discovering an existing objective reality “out there”, not a process of

creation which is relative to the apparatus—for example, language, or

the senses—we use for the inquiry. This notion of objectivity and

invariance of standards—of being able to say what X is—applies to

ethics and aesthetics, as well as science and mathematics; without

fixed reference points for the meanings of classificatory terms, all

significant talk about the world would be impossible; the world

would be a stream of unique ineffable particulars. The meanings of

words are, or can be, determined by the nature of reality—in existing

objective references—not the other way around. And if knowledge is

24 Greek philosophy

possible, it must be knowledge of objects which are real; and this

requires that knowledge be knowledge of what is; that is, objects that

are not in states of becoming, but are eternal, immutable beings. To

make our meanings match the world as it really is, is to seek true or

real definitions, and requires objects, which the definitions are

definitions of. The meaning of the word “justice” is not, in Plato’s

view, a mere conception in the mind, but is fixed mindindependently.

In agreeing with Heraclitus that the sensible world is in flux, Plato

realizes that the objects of such definitions are not going to be found

among imperfect and mutable sensible objects, but exist in a

supersensible realm of immutable objects “seen” by the intellect

beyond sense-experience. In the world we never find justice-in-itself,

but only conditional justice. One can always find conditions in which,

derived from a changing world or a different point of view, a just

action ceases to be a just action. Plato thinks there has to be something

that is invariable and common which corresponds to the meaning of

universal terms such as “justice” or “bed”, that exists over and above

the variety of particular instances that terms—such as “justice” or

“bed”—cover, and that justifies the classification or grouping of

various different things as of the same sort or class. What we mean by

“horse” in general, if it is meaningful at all, is something other than

any particular horse, each of which differs; each horse is a horse

because of its sharing in a nature common to all horses.

It is from the search for definitions of universal, immutable, ethical

standards that Plato’s theory of Forms emerges as the basis for all

knowledge (epist¯em¯e) in its full sense. Plato turns Socrates’ search for

definitions, aimed at understanding the nature of what we are talking

about, into an ontological claim whereby the real meaning of

classificatory terms requires a reference in a transcendent object or

Form (eidos). It is not just knowledge of ethical truths that requires the

Forms, but all claims to knowledge. Indeed, it applies to knowledge

itself, for if we cannot suppose there is some fixed meaning for the

term “knowledge”, referring to some fixed object, knowledge-in-itself,

then surely intellectual chaos must ensue. Plato assumed that for a

word to have any fixed objective meaning, this must be in virtue of a

fixed and objective entity to which the word refers. This assumption

can be questioned.

It is essential for the understanding of the theory of Forms to see

why epistemology and metaphysics are so closely connected in Plato’s

philosophy: the nature of knowledge should be matched by an

appropriate ontology. Knowledge is always knowledge of something, and

Plato requires these objects of knowledge to bear in their mode of

existing (the way they are as objects) the same characteristics as the

knowledge we have of those objects. For Plato, two main conditions

have to be met for the highest sort of knowledge.

Plato 25

(a) Universality or objectivity

Knowledge of something is not relative to a point of view;

knowledge should be something that would be true from any

point of view.

(b) Unchangingness, eternality or immutability

This requires that knowledge is unchanging over time; that if

something is knowledge, then it is knowledge once and for all;

it cannot cease to be knowledge. Knowledge in its highest

sense is infallible: it is absolutely certain. If one really knows

something, there cannot be conditions under which what one

knows is wrong, and ceases to be knowledge. So one knows

only what must be true—necessary truths—and cannot be false,

and when there is a method of demonstrating conclusively that

the known truths are necessary truths.

There are two factors that make the world of sensible objects

unsuitable for knowledge.

(a’) That things and properties in the sensible world are not fully real,

since they are not unconditionally what they appear, as how they

appear depends on a point of view. Sensible things can take on

contrary properties for this reason as well if one’s point of view

changes; the properties sensible things appear to have is therefore

determined partly subjectively.

(b’) That things in the sensible world are constantly changing. In this

way sensible things can take on contrary properties over time; the

sensible world is one of becoming.

Anything that can take on contrary properties cannot be fully real, since

it never unconditionally just is, and we cannot be said to be knowing

things as they are in themselves. Plato gives strict conditions for

knowledge: certainty, universality and immutability. He further needs to

show, if knowledge is possible, how we can satisfy those conditions; the

Forms of the theory of Forms provide objects which satisfy the

conditions for knowledge. Knowledge is knowledge of something; that

is, it requires an existing object; there must be objects of knowledge that

match the characteristics of knowledge proper (knowledge in its full

sense) itself if such knowledge is possible at all. These objects are the

Forms. The Forms are not objects in the sensible world; sensible objects

both are mutable and have properties that vary with one’s point of view,

and so are not fully objective; nor are the Forms posited entities that

underlie appearances in the way that atoms do. Forms subsist beyond

the flux of experience and space and time in a transcendent,

supersensible realm that is ultimately perceived purely by the intellect.

The Forms are pure objective essences, and as the objects of knowledge

they match the characteristics required of knowledge itself. As opposed

to the “thatness” or existence of things (that X is), the Forms define the

26 Greek philosophy

“whatness” or essence of things (what X is); the Forms give necessary

and sufficient conditions for things to be the kind of things they are. The

Forms have the following important characteristics.

(a’’) Universality or objectivity

There is no point of view from which the Form of F could be

sometimes F and sometimes not-F; if something can be both F

and not-F depending on a different point of view or different

circumstances, then we cannot have found F-in-itself: the Form of

F. The Forms are also what is universally or objectively true from

any point of view. Apprehending what things-are-in-themselves

is to grasp their Form. As well as being objects of knowledge in

themselves, the Forms are the extent to which anything can be

said to be universally or objectively true of sensible objects apart

from their various appearances.

(b’’) Unchangingness, eternality or immutability

Since the Form of F is immutable and indeed eternally what it is,

there is no time at which the Form of F can become not-F, it is

eternally F. Forms are fully real in that they are not characterized

by any becoming; they are being. They are what a sensible object

which copies or participates in a Form really is apart from its

changing states. The Forms are separate in some sense from the

world of sensible objects and their nature grasped by the senseindependent

intellect; their separateness seems to consist of real

existence or ontological independence apart from both sensible

things and minds.

Taking (a’’) and (b’’) together gives the conditions for the mode of

being of fully real existence, and this matches (a) and (b), the

conditions for knowledge proper.

Plato seems to hold that the realm of Forms is separate from the

realm of sensible objects, but exactly in what this separateness consists

is not clear. The sensible world is ontologically secondary; although

later in life Plato became more interested in natural science. It is worth

noting that since the Forms are not in space or time, it is senseless to

ask where the Forms are. It is the ontological separateness of the Forms

from particulars which is criticized by Aristotle.

It may not be immediately obvious why we cannot be said to have

knowledge of particular truths. Surely I can know that “there is a table

in my room”? However, it is worth noting that, regardless of its

certainty, we would hardly regard this as a piece of scientific

knowledge; it is not a universal explanatory law. Plato does not deny

that something beyond ignorance is possible in these cases: we can

have belief (doxa) which is true. But the highest form of knowledge,

knowledge in its full sense, is of universals or objective essences.

Knowledge proper is not of this or that table, but of tables-inthemselves:

knowledge of what is involved in something being a table:

Plato 27

tableness. Knowledge proper transcends the bounds even of all

possible experience, and involves an intellectual “seeing” that reveals

things as they are in themselves. If something is known in the highest

sense to be true, it cannot become false. If X is known, then necessarily

it is true that X. Plato goes further in holding—although it does not

follow from the assertion that knowledge entails truth—that if X is

known, then X is a necessary truth. Plato holds that what is known

must be true in the sense that what is known is only necessary truths;

knowledge is of things that could not be otherwise. If what is known

ceased to be true, it would cease to be knowledge. Take the example

“This water is hot”. The problem here for knowledge is that (a) “This

water is hot” can be true for one person, but false for another, and (b)

the water is something that is in a state of becoming (becoming cold

perhaps), so “This water is hot” is true, but will become false. That

which has no fixity cannot have true descriptions applied to it, for

what is true becomes instantly false.

The model for the ideal of knowledge is to be found not among the

mutable and relative truths concerning sensible objects, but among the

eternal and universal truths concerning the objects of mathematics and

geometry which are known by the intellect. The truths of arithmetic

and geometry concern not this or that object (say, a particular triangle),

or this or that set of objects (say, two pairs of objects), but rather

triangularity and 2+2=4. Knowing the truth 2+2=4 does not concern

any particular two objects, which might through change become one

or three objects, or which only look like two objects when viewed in a

certain way, or any sensible objects at all. Knowing the truth 2+2=4

concerns twoness, and its relation to other essences, such as equality,

addition, and fourness. This is not a truth that varies over time; indeed

it is eternal or timeless, and stands outside time; and, as such, this

known truth requires an eternal object of which the known truth is

true; that object is a Form or combination of Forms. The objects of the

sensible world are not suitable objects for such necessary, objective,

immutable truths. Take the example of equality: if we have two sticks

of equal length, and also observe that they are six feet long, we may be

tempted to say that being equal (equality) consists in being six feet

long; but there are circumstances in which being six feet long would be

both equal (F) and unequal (not-F); so we do not yet know equality-initself

because we have identified something—being six feet long—that

can be both equal and not-equal, whereas to know what equality-initself

is is to know it irrespective of changes over time, point of view, or

conditions. Equality as such must also be what all cases of equality

have in common irrespective of their particular differences.

The world of Forms is “perceived” by reason or the intellect, not the

senses; the Forms are objects of intellectual vision or looking.

Geometrical truths concern not this or that circle or triangle, nor

even generalizations about all empirical circles and triangles which are

28 Greek philosophy

also approximate and imperfect, but circularity and triangularity as

such known by the intellect alone—in short, they deal with essences—

with the Xness of objects under the common name “X”. It must be

noted that mathematical truths are one step down from knowledge of

the Forms themselves because mathematics still involves unquestioned

assumptions; but since mathematical truths known by the intellect

alone are superior in certainty and immutability to the deliverances of

the senses, they can be used as a stepping stone toward knowledge of

the Forms.

At a lower level than mathematics, we can further understand the

Platonic ideal of knowledge, and the requirement that it be objective,

through analogy with scientific laws of nature: Newton’s first law of

motion, “Every body continues in its state of rest, or of uniform motion

in a right line, unless it is compelled to change that state by forces

impressed upon it”, is not a law applicable only to particular bodies, or

bodies considered from a certain point of view; it at least applies to all

bodies at all times and in all places. Moreover, it may be said to apply

to bodies-as-such; that is to say, it is a truth which can be known about

the essence of bodies; to be concerned with the essence of bodies is to

be concerned with what all and only bodies have in common, that

which is necessary and sufficient for them to be bodies, which is

correctly called “body”.

It may be concluded that if knowledge of the Forms is the only true

knowledge, then there can be only ignorance of the objects of the

sensible world, and therefore that the sensible world is neglected by

Plato. But this is not the case. That the world perceived by the senses is

not fully real because it is subject to becoming (it never just “is”), and it

cannot be the object of universal, immutable, unconditional truths,

does not mean that it does not exist. The existence of immutable Forms

divides the world into various fixed kinds of things as they are in

themselves, and is the formal and final cause of the sensible objects in

the world (the world of becoming) having whatever limited degree of

being of which they are capable. “Cause” should be understood here in

a more general sense than that to which we are accustomed: causation

is an answer to a “Why?” by a “Because…”. The Forms are “formal

causes” in giving definite character to things which we bring under

common names (“man”); the Forms are “final causes” as the perfection

towards which that kind of thing aims as an end. As formal causes, the

Forms are a precondition for our saying of anything that it is

something of a specific kind; they define and make definite things as

objects of a certain type; they are thereby causes by giving definite

character and a limited degree of type-identity to the flux of the

sensible world.

Although Plato never answers the point, one assumes there must

be some limit to the number of classificatory divisions; if every

positive common name has a Form, then the danger is of an

Plato 29

unlimited and unknowable world of Forms. Relative terms such as

“large” are also problematic. Although the Forms do not give us

eternal, immutable particular sensible objects—for only universal

kinds or types are eternal and immutable—they give to sensible

objects a stability somewhere in between the being and non-being of

Parmenides, avoiding thereby the universal becoming of Heraclitus;

and of these sensible objects of relative stability we are able to have

true beliefs, if not knowledge. Plato points out that “is” does not

always mean “exists”. The exhaustive choice is not being X

(existence) and non-being X (non-existence or nothing); for we can

say that X can be an X while losing some properties and gaining

others. To say that a person X was hairy and is now bald is to say

there has been a change in X not from existence to non-existence, but

from being hairy to X being not hairy (bald). At the same time, Plato

attacks Protagoras’ relativism, which claims that universal objective

knowledge is not possible at all, and that we are merely left with

particular knowledge claims about immediate experience, which are

perhaps infallible (cannot be mistaken) in themselves, but which are

true only from a certain point of view at a certain time, with no claim

to universality or generality at all.

Plato’s answer to both Heraclitus and Parmenides is the Forms.

Plato agrees with Heraclitus that the world of sensible objects is

ultimately in flux, and he agrees with Parmenides that the intellect

alone knows the true nature of reality. Knowledge proper is of

immutable and eternal truths and must concern the nature of

immutable, eternal objects that really exist; but the sensible world

reveals only mutable, non-eternal objects; therefore, if knowledge is

possible, it must concern a realm of immutable, eternal objects that

really exist, beyond sense-experience, that are intuited or seen by the

intellect alone; those objects are the Forms.

Plato’s epistemology and metaphysics mirror each other: the Forms

which have only being are fully knowable; of utter non-being there can

only be ignorance; but in between these is the sensible world of

becoming of which there can be true belief which lies between full

knowability and complete ignorance. This gives the following picture.

Being (Forms) – knowledge

Becoming (sensible world) – true belief

Non-being (nothing) – ignorance

The way to approach true knowledge is by the method of dialectic:

giving, improving, and eventually destroying, hypotheses—

assumptions used for justification in the sense of reasoned grounds for

what we claim to know. Claims to knowledge are thereby based on

fewer and fewer, and different, assumptions. For it to be said that I

know X, it has to be the case not only that I have beliefs, even if they are

true, concerning X, but also that I can give an account of why it is true

30 Greek philosophy

that X, or what X is; a proper account or justification marks the

beginning of the distinction between belief and knowledge. Giving an

account of X is saying what it is that makes it X. The account that I give

may be based on assumptions which are not themselves beyond

question. If I try to account for X being true by deducing X from certain

premises, then it can be asked what justification I have for these

premises. I can answer this challenge by deducing the initial premises

themselves from more general premises. The method of hypothesis is a

process of questioning and testing deduced consequences of hypotheses.

The intellect or thought transcends, in mathematics, hypotheses about

the imperfect, approximate, objects of experience. We successively

ascend from hypothesis to hypothesis, until we eventually reach the

Forms, and ultimately the “First Principle” or highest Form the “Good”

or “Being” or the “One”, which is said to transcend even being, and

which is self-authenticating (unhypothesized) and destroys the need for

hypotheses.

Another related description of the dialectic found in the later work

of Plato is the method of division and collection: this is the process of

collection and division into genera and species, and it suggests a

hierarchy of Forms; the Forms are complex wholes which are divided

through genus and difference by species. The logic of the dialectic is

matched by an ontological process; the logical collection of species

under genus is like the blending into one another (in the manner of

colours) of different Forms. The aim of division in the dialectic is to

give real definitions of terms referring to indivisible “atomic Forms”

(infima species) such as “man”, “horse”, “tree”, that have no sub-species

and designate species or universals, not particulars or individuals. The

“atomic Forms” cannot combine at all: so the expression “man horses”

makes no sense at all. The hierarchy of Forms is describes a hierarchy

of reality or degrees of being proportional to permanence and

generality. Below the “atomic Forms” there are only individuals (for

example, individual men), not further species. Alternatively we can, by

collecting species, ascend in the hierarchy to ever more pervasively

general categories of being, to Forms of ever richer content and greater

degrees of being. It has also been suggested that Plato envisioned some

kind of mystical road to the highest Forms, as well as the rational

dialectic.

Plato’s view on epistemology and metaphysics can be summarized,

although not entirely in his terminology, in the following way. Reality

should determine language to give objective concepts which are not

our creation, but rather fixed, and imposed upon us. The highest sort

of knowledge is of objective necessary truths, which are discovered by

the intellectual inspection of the ways that non-conventional objective

universal concepts—discovered and not arbitrarily created—are

connected or not connected to each other. The necessary connections

concerning the highest sort of knowledge are found by intellectually

Plato 31

seeing the inclusion or non-inclusion of the true meanings of common

words—concepts—in each other. These concepts are objective in

describing the real eternal immutable nature of the Forms, which are

real eternal immutable objects. Some Forms are the essential features of

the objects to which common names refer, and determine and tell us

what each thing is in itself. The essential nature of a thing includes

only those features which are necessary and jointly sufficient for it to

be the kind of thing it is. The essential features are revealed in a true or

real definition of what it is for a thing to be of a determinate kind.

It is important to see that for Plato the concern is not with the

necessary connection of propositions, or merely with the meaning of

words, but with the nature of the objects the words stand for: real

immutable eternal objects—the Forms with the required characteristic

of being—understood by the sense-independent intellect through their

descriptive concepts revealed in definitions or formulae. These

ontological connections are revealed by linking the true meaning of

terms which name Forms, given by a true description of essences in

real definitions (providing a correct account or logos), which give

concepts of eternal existing objective Forms. The connection of these

concepts which name Forms is seen by the intellect in the inclusion or

non-inclusion of the meaning of one concept in another. This produces,

in the case of inclusion, a logically necessary truth concerning the

connection of the objects referred to. Such necessary connections,

which depend only on the inspection of correct meanings, produce

truths logically independent of experience. We can know necessary

truths by showing conceptual connections; and such necessary truths

are necessary because the terms in these truths have as their reference

eternal immutable objects—Forms—which are not, and cannot be,

objects of sense-experience, but are objects of the intellect. The dialectic

method is deductive, ensuring that knowledge is infallible (nonrevisable)

and certain; a truth known by the correct use of the method

cannot be shaken by new evidence. The dialectical method for

justifying truths cannot be valid by degree. It provides a way of

making the justification element in our knowledge a conclusive logical

proof: it is a valid argument deduced from necessary truths. In this

way the necessary truths which are known are conclusively shown to

be necessary, and hence to have the absolute certainty and

immutability required of knowledge proper.

The Platonic dialectic of collection and division approximates to the

modern notion of analyticity, and the discovery of analytic truths; but

Plato thinks that these are objective truths (they are true of the Forms)

and independent of the factual conventions of linguistic usage.

The inclusion and non-inclusion of meanings can be illustrated as

follows: “man” is included in the concept “animal”; and under the

concept “animal” falls the array of different animals; so “man is an

animal” is a necessary truth; whereas plainly “man” does not, and

32 Greek philosophy

indeed cannot, include the concept “fox”. Man and trousers are

connected, if at all, only contingently because the concept “man” (real

meaning or definition of “man”) does not include “trousers”; so “man

wears trousers” is not an eternal truth, and is not an object of the

highest knowledge (epist¯em¯e), but a matter of belief (doxa), perhaps true

belief, about a contingent fact in the sensible world.

No necessary truths picking out necessary connections can be

discovered in the sensible world; yet this is required if knowledge of

the sensible world is possible—in the highest sense of being absolutely

certain or infallible and eternal. Otherwise there are only correct

beliefs concerning contingent truths in the sensible world. If what is

known is a necessary truth, and can be shown to be a necessary truth,

then it is absolutely certainly known, since it is impossible that it

could be false. In any case, knowledge of the sensible world is

dependent on the availability of the absolute objective fixity of the

concepts we bring to the world, and this is guaranteed only by the

absolute objective fixity of concepts’ references in a real, supersensible

realm of Forms “perceived” by the intellect. Whether, and how, such

Forms, articulated in concepts, can be connected with the sensible

world is a difficult question. But even to say of anything that it “is X”

(“is yellow”) is to use the concept of being (being X) that goes beyond

the particular yellow percept, which may change. In the same way

being able meaningfully to say “that is a man” presupposes the

conceptual fixity of “man”. Plato thinks that meaningful talk about the

world must involve both that there must be absolute conceptual fixity

of meaning and also that such meaning is derived from a special

object: a Form.

There is an ascent to the Forms, and through the hierarchy of Forms,

until what we claim to know is a truth, where the justification is

deduced, by way of the relation of real definitions, from a startingpoint

which is self-authenticating, completely certain, and involves no

assumptions. We aim to ascend to this “First Principle”, from which

we see the whole of reality as a connected rational system based on the

absolute objectivity of the Forms. To the extent that anything like

knowledge of the sensible world is possible—and Plato’s interest in

natural science increased in later life—it involves a downward

dialectical process in the hierarchy of Forms: in this, one initially

proposes the most general class to which the thing to be defined (the

definiendum) belongs, until through division by similarity (by genus)

and difference (by species) we have specified the narrowest class the

thing defined belongs to; then we shall have knowledge in the fullest

sense of what the definiendum is: this gives the necessary and sufficient

conditions for a thing being the kind of thing it is. For example, the

definition of “triangle” combines the genus of “triangle” as “polygon”

with the species of polygon “having three sides” into “polygon having

three sides”. This fixes what a triangle is.

Plato 33

The taxonomy of the unchanging hierarchy of Forms is the true

object of knowledge. Through the Forms is revealed, in the terminal

definitions by genus and difference, the essence of things sharing a

positive common name. We also come to know the rules of

combination or blending of those Forms, since not all Forms can blend

together. An assertion suggesting the blending of incompatible

Forms—“motion is rest”—is a contradiction.

False judgements are not about nothing, but concern elements which

exist—say, the particular Theaetetus and the Form flying—but which, in

combination, are judged to assert falsely “Theaetetus flies”. Indeed,

every meaningful statement involves at least one universal or Form.

Through studying the interrelation of the Forms we come to know the

true unchanging or eternal structure of reality. The highest Form—the

“Good” or “Being”—is the genus of all that is real; a real whole

covering—common to—all and only that which is real. That is, the

highest Form is the essence of reality as such. The Forms exist in a world

that transcends both the physical and mental, while they are somehow

related to particulars. The Form of the “Good” or “Being” is the aim and

aspiration of all things, the ultimate ground of the world’s intelligible

reality through defining the nature of being or reality itself or as such.

Our ability to have knowledge of the Forms, transcending the

sensible world, is explained by Plato’s theory of recollection. One way

of interpreting this theory is to see it as Plato’s attempt to account for

the possibility of a priori knowledge; that is, truths known by the

intellect alone independently of sense-experience. At some time before

we were born, our immortal soul was disembodied and was thereby

not confused and distracted by sensible particulars. Our soul is part of

the eternal realm, and so able through pure reason to grasp the nature

of the Forms themselves. Indeed, the possibility of knowledge of

essences—the Forms—is taken as proof of our immortality. Sensible

objects remind us of the perfect Forms we have forgotten, of which

sensible objects are imperfect copies, and which have being only in so

far as they partake of the immutable divisions of reality or being of the

Forms. The extraction of universals by comparing sensible objects with

a common name can be a starting-point for reminding us of the Forms,

but it is not sufficient for knowledge of the Forms; rather, a productive

starting-point of classification assumes that it is an objective

classification contained in the Forms of which the classification of

particulars reminds us.

It is tempting to think of the Forms as perfect particular instances of

sensible objects. But this cannot be so. Plato was aware of this in the

“third man” argument: if all the instances of X are instances of X by

having in common some feature embodied in the Form X (Xness), and

the Form of X is itself an instance of X, then all the instances of X and

the Form of X taken together are instances of X only in virtue of some

further Form embodying common features in virtue of which all the

34 Greek philosophy

instances of X and the Form of X itself are X. And so on to infinity.

There is no doubt that the nature of the relation of the Forms to

sensible particulars presents Plato with difficulties, whether this

relation is said to be one of copying or resemblance, or one of

participation. If the relation is one of resemblance, there is the problem

revealed in the “third man” argument. If the relation is one of

participation, then we have the dilemma of deciding whether the Form

is present in each instance in its entirety or whether each has a

different part of the Form: in the first case the Form which is supposed

to be one or unitary is yet in its entirety in many individuals, in the

second case we lose anything common to, or the same in, all the

instances, and the Form is both one and many or divisible.

One way of thinking about the Forms is to consider them not as

entities which are perfect instances of sensible particulars, but more as

akin to formulae known by the intellect. This brings to mind the

Pythagoreans, for whom Plato had some sympathy. There is a

completely general formula for a circle, but the formula is not itself

circular or an instance of circularity; the formula may be verbal as “a

plane figure bounded by one line every point of which is equally

distant from a fixed point called the centre”, or as an algebraic

equation. In the same way the formula or definition of man or bed is

not itself an instance—even a perfect instance—of a man or a bed.

The main feature of Plato’s achievement is perhaps the way he laid

down the highest standards for knowledge as absolutely universal,

certain and necessary—a standard for which scientific knowledge has

striven. The standard is too high for natural science. Nevertheless, it

points scientific knowledge away from the particular case toward

unifying and inclusive truths of greater general explanatory power and

scope. Science does not deal with particulars, which in their full

particularity are unknowable, since the inevitable use of universal

terms means they can never be pinned down in their unique

particularity. Scientific knowledge deals with generally applicable

unifying truths concerning the underlying common or general features

of an apparently enormously diverse world. Thus it will concern itself,

at one level, not with this table and that table, or tables and cows, in so

far as they differ and are particular, but with giving a unified

explanation for their behaviour under their common nature or feature

of all being bodies or material objects. Science is concerned with the

structure or nature of an underlying general explanatory reality which

is fully objective and rationally understandable.

Aristotle

Aristotle (384–322 BC) was born the son of a prominent physician, in

Macedon in north east Greece. The medical interests of his family

Aristotle 35

encouraged his own later detailed empirical works in biology, which

influenced his philosophical outlook. At the age of seventeen he

became a student of Plato’s Academy, and later a teacher there. In the

early days he was generally in agreement with Platonic philosophy,

paying particular attention to the Phaedo, and only later, in important

respects, did he reject Plato’s philosophy. Nevertheless, he continued

to share Plato’s opposition to scepticism, and agreed that knowledge is

possible; it is on how the sceptical problem is to be solved that they

differed. Aristotle was predisposed to take a greater interest than Plato

in the natural world, of which Aristotle thought knowledge is possible.

Following the death of Plato, Aristotle left the Athenian Academy, and

was eventually tutor to the heir to the Macedonian throne, Alexander

the Great. Aristotle returned to Athens in 335 BC, and taught at the

Lyceum; but following the early death of the all-conquering Alexander,

resentment arose at the Macedonian domination of Greece and the

city-states; this made Aristotle’s position in Athens, as an alien with

Macedonian connections, increasingly uncomfortable. A charge of

impiety was brought against Aristotle; rather than be the central

character in a replay of the fate of Socrates, he left Athens in 323 BC.

Unable to return home to Stagira, the city of his birth, which had been

destroyed, he went to the remote city of Chalcis, where he died in

lonely exile in 322 BC at the age of sixty-two. He married twice, having

been once widowed; by his second marriage he had a son,

Nicomachus.

The philosophy of Aristotle owes a great deal to Plato. First,

although Aristotle rejected Plato’s theory of real separately existing

Forms, he held on to the notion of forms as the unchanging reality

providing the basis for knowledge proper of what things are. Plato’s

intelligible Forms are essences or defining formulae that really exist as

separate entities transcending the sensible world and minds.

Aristotle’s intelligible forms are immanent (in-dwelling) in sensible

particulars, and cannot, unlike Platonic Forms, exist apart from

particulars; the Aristotelean forms can be separated from particulars

only in thought, although they are objective and not subjective or

mind-dependent. Second, Aristotle supports anti-mechanical,

teleological methods of explanation. Teleology is not so much an

empirical hypothesis as a decision to adopt a certain method of

explanation. It aims to explain why things are as they are by referring

to the ends to which they aim; the end is being perfect, or fully

developed, specimens of the kind of things they are. It is reasonable to

see Aristotle as synthesizing Platonic realistic abstraction with a

concern to explain the natural world found among the Presocratics.

Aristotle agrees with Plato that knowledge proper or scientific

knowledge (epist¯em¯e) must be certain and necessary; knowledge is of

invariant or unchanging universal necessary truths. Knowledge must

be knowledge of something. Aristotle shares with Plato the notion that

36 Greek philosophy

if knowledge is possible, knowledge must be of what is real, and what

is real is eternal and unchanging. In short, the necessary truths we

know must be matched by their referring to ontologically suitable

objects.

Aristotle rejects Plato’s solution of positing as the true objects of

knowledge a realm of separately existing essences, the Forms: first,

because he thinks it only duplicates our problems concerning

knowledge of the world, and second, because Plato gives no clear

account of how individual objects in the world are supposed to

participate in, or resemble, the Forms.

Knowledge for Aristotle consists in a systematically connected set of

disciplines. Metaphysics (First Philosophy) is the most general and

fundamental aspect of all knowledge because it studies being qua

being. Unlike each individual science, metaphysics examines not this

or that sort of thing, but existing things, or being, as such; it restricts

itself to understanding that which is common to all and only things

which are real and have being; it studies those features of things which

they have merely in virtue of their existing as real things at all.

If the world is in constant flux, as Heraclitus suggests, then it cannot

contain eternal unchanging objects suitable for knowledge. If we

adopt, on the other hand, a Parmenidean view, all change and

plurality in the world are illusions, for they involve logical

contradictions: F becoming not-F; hotness becoming coldness.

Atomism may seem to point to a way out, for atoms remain the same

(have being) through change; indeed change is simply a rearrangement

of the same atoms. Aristotle rejects atomism (or materialism) because

collections of atoms do not do justice to our common-sense, or pretheoretical,

notion that there really are separately existing individual

instances of kinds of things. Atomism allows no distinction in kind

between a mere heap of bricks and a horse which is a genuine

substantial separable, hence bounded, kind of thing. Although a brick

may be an instance of a “so-and-so”, a heap of bricks is not identifiable

as a new “this so-and-so”. Matter alone is not a “this so-and-so” (it

does not pick out, say, this horse), for it is common in its nature to

different kinds of particulars, and thus cannot differentiate between

them as particulars of different types.

The important point is that the talk of the kinds of things there are

in the world which concerns Aristotle corresponds to real or natural

kinds; the way things are grouped together by kind, if properly

carried out, marks real objective divisions in the world made by

nature herself, not merely the arbitrary or subjective classification

into groups imposed by us on individuals which are in some way

similar.

For these reasons Aristotle posits substance as that which has

identity or stability through change. Aristotle notices that when we

talk about the world we distinguish between certain factors that alter

Aristotle 37

and certain factors to which the alterations occur which can remain the

same. Substances are, in a sense, pivots around which change occurs.

This is supported by the logical analysis of the carrier of all true or

false assertions about the world: the proposition. In Aristotle’s view

propositions always contain two elements: the subject and the

predicate. Predicates are what is said to be true or false of subjects.

Subjects can remain the same while having different, or indeed

contrary, predicates applied to them, and predicates logically depend

on there being subjects.

Predicates, whereby we say things about subjects, can be grouped

in different sorts or categories that are the highest genera or classes of

being and together may cover all modes of being. Aristotle gives the

ten genus categories as: substance, quality, quantity, relation (which

are the chief categories), place, time, less temporary condition/state,

more temporary condition/state, activity, passivity. Under the genus

category of relation, how something is related to other things, there is

among others the species of spatial relation, an example of which is: X

is to the left of Y. The metaphysical counterparts of subjects and

predicates are what these terms stand for. The most fundamental

category is that of substance; predication in this category tells us,

concerning the subject of a proposition, what kind of thing it is: X is a

horse. To say what kind of thing X is, is to give its essence; the other

categories of predication are of accidents, and these depend

ontologically on, and are always predicated of, substances. The

essence or “whatness” of a thing is given in a real definition or

formula which provides the necessary and sufficient conditions for a

thing to be what it is; an essence is what is common to all and only

things of a specific sort in virtue of which they are the sort of things

they are. This is a logically separate question from whether there

exist things of that sort: the existence or “thatness” of a thing. In

short, the essence refers to what it is to be an X; the existence refers to

the fact that there is an X; and one can know what an X is without

knowing that an X is. The essence of X therefore defines what we

mean by an “X”.

A term such as “horse” is a species substance term identifying a

species of a substantial separable way-of-being; a species quality term

such as “pale” is a non-substance term identifying a species of a nonsubstantial

non-separable way-of-being. In either case, contrary to

Plato’s theory of Forms, there cannot, metaphysically speaking, be

universal attributes such as horseness without horses or paleness

without some object or other that is pale. But whereas an instance of

the way-of-being of a substance never depends for its way-of-being on

its predication of any other way-of-being, the way-of-being of a nonsubstance

always depends for its way-of-being on its predication of

some other way-of-being. This indicates that the relation between

substances and accidental attributes is asymmetrical. It always makes

38 Greek philosophy

sense to ask, if any non-substance term such as “pale” is applied,

“What is it that is pale?”. It makes no sense to ask, if a substance term

such as “horse” is applied, “What is it that is horse?”. The logical point

about subjects and predicates, and the corresponding metaphysical

dependence of some ways-of-being on others, led Aristotle to

formulate two senses of substance.

(a) It must be that which is always a subject of predication, and never

predicated of any subject.

(b) It must be that which has an independent or separate way-of-being

or mode of existence.

What satisfies these formulations, and is substance in the primary

sense, is concrete individuals of various identifiable kinds that can

exist separately: they are those instances of whatness or ways-of-being

that have a separable existence. These are independent subjects which

can undergo certain changes while they remain identifiable as the

same kinds of individuals. Substances are still pools of being in a sea of

accidental becoming which avoid the conclusion that every change of a

subject of change is a change in the subject of change. The subject

Socrates can change from young to old, pale to flushed, and yet he

remains the same individual: an instance of a man. The Greek word

Aristotle uses for substance, ousia, is derived from “to be”: substances

are the most primary ways-to-be identifiable as “this so-and-so” (the

Greek is tode ti), of which all other ways-to-be are predicated modes,

and on which those other ways-to-be are dependent for their existence

as ways-to-be. Paleness as a way-of-being depends for its existence

both on some instances of paleness and on objects of some kind or

other being pale; but the instances of kinds of objects which are pale, if

they are substances such as this man, are not dependent on their being

predicated of instances of any other kinds of being.

Primary substances are not, however, the objects of science. Science

studies universal necessary features of the objects of the world, not this

or that object in its particularity. Aristotle supports the commonsense

or pre-theoretical view that individuals fall into determinate natural

kinds of things. Thus individual men fall into, and are instances of, the

natural kind man, and individual horses fall into, and are instances of,

the natural kind horse. Aristotle refers to the universal predicates that

define the properties that individual instances of a natural kind must

have in order to be the kind they are as substance in the secondary

sense: substance because they are the objects of science, secondary

because the being of a certain kind as such is dependent on there

existing individuals or instances of that kind. There cannot be

independent “so-and-sos”, or bare types as such, “floating” around,

unattached to particular “thises”; there cannot be the universal essence

horseness existing without there being particular horses existing. So

we have two meanings of substance:

Aristotle 39

(1) Primary substances: individual instances of the class of universals,

designated by a certain category of predicates, which can exist

separately being what they are—“this so-and-so”, this X, this man,

this horse.

(2) Secondary substances: the universals, designated by a certain

category of predicates, which are the properties defining real or

natural kinds or what something is, of which primary substances

are instances: “so-and-so”, Xness, man, horse.

Logically speaking, secondary substances are a special class of

predicates. The secondary substance predicates designate certain sorts

of property, the sorts of property which are the essential defining

properties of a thing that tell us what a primary substance is, and

which it cannot lose without ceasing to exist as the kind of thing it is.

In addition there are non-substances:

(3) Non-substances: the classes of universals and particulars,

designated by certain categories of predicates, which are not

capable of independent existence as identifiable instances of kinds

or ways-of-being—X, a heap of bricks; Xness, paleness.

The categories of universal predicates which identify non-substantial

dependent ways-of-being are accidental properties; these are properties

which a primary substance can gain or lose while continuing to exist as

the kind that it is, that is, while remaining the same identifiable kind of

individual.

In the case of (3), non-substances are not primary substances, either

because they are not capable of separate existence as instances of what

they are (for example, paleness) even though they may designate a

universal, or because they are not identifiable individual kinds or

ways-of-being at all (for example, a heap of bricks) even though they

are capable of independent existence.

A genuine substance must for Aristotle satisfy two conditions: it

must be both a determinate instance of a “so-and-so” or “whatness” of

some identifiable sort and also capable of separate existence as that

way-of-being such that it is not a modification or qualification of the

way-of-being of any other thing. A substance is both an individual

instance of a universal—an identifiable “this so-and-so”—and a wayof-being

that can exist separately, not as a mode of any other

identifiable “this so-and-so”. This man or Socrates satisfies both the

conditions for being a substance: it is both identifiable as a “what”—an

individual instance of man—and has a separate or independent

existence, is not a way-of-being dependent on the modification of any

other thing. In short, substances are the class of particular whatnesses or

ways-of-being that do not depend for their existence on being

modifications of any other thing or way-of-being.

Thus Socrates is a primary substance both because he is an instance

40 Greek philosophy

of the identifiable universal way-of-being man (unlike a heap of bricks,

which is not an instance of a universal way-of-being at all), and

because the way-of-being which is a man does not depend for its

existence on the modification of any other thing or way-of-being

(unlike an instance of paleness which depends for its existence on

being a mode of some other thing). An instance of paleness depends, in

a way that an instance of man does not, on there being some other

thing—for example, this man or Socrates—which is pale; logically

there cannot be an unattached instance of paleness without a subject

which is pale; there can logically be unattached instances of Socrates.

Primary substances are compounded of two elements,

(a’) matter (hyl¯e)

(b’) form (eidos, morph¯e).

By “matter” here is meant something more general than the physical

stuff out of which it is made; what is meant by “matter” is whatever it

is that takes on a certain determinate form, which thereby turns a

“this” into a “this so-and-so”. The form of a thing is immaterial and

structural, and it is what gives matter a determinate character as a

certain kind of thing. The form is the structure or shape the matter has

which makes it a determinate kind of individual or instance of a

kind—rather as there might be two brass keys (they are of the same

matter: brass), but only one fits my front door (they are of different

forms: shape). So matter is that which is “informed” as an identifiable

kind of thing, and form is that which makes some matter something of

a certain kind: the whatness, or being-what-it-is, of each individual. In

this sense any matter as such is potential substance, which is actualized

as substance when it takes on a form and becomes a “this so-and-so”.

The meaning of “matter” here is not restricted to physical stuff:

“matter” might be a man’s general character that takes on the form

“bad” so he has a “bad character”.

The connection between the secondary substances and the forms—

(2) and (b’) above—is that secondary substances are instantiated in

particular instances in matter as the form of that matter; the “so-and—

so” of a “this”, giving a separately existing individual, “this so-and-so”

of a certain kind or sort. The form or essence is what all and only

individuals sharing a common name and falling into a natural kind

(marking a natural division in nature such as horse) have in common

in virtue of which they are the kind of things they are. It perhaps helps

to understand what is meant by matter taking on a determinate form,

while also seeing that form is not a separate entity, to think of stone as

a petrifying of matter, and of a horse as an equinizing of matter.

Matter and form are the logical parts of substance (apart from God

who is pure actualized form); they always occur together and can be

separated only in thought; we never find “prime matter” devoid of all

specific determinations. Anything said of something posited as prime

Aristotle 41

matter would show it not to be prime, because the ability to talk about

it and say what it is would necessarily involve saying that it has some

specific characteristics or whatness. Prime matter is literally ineffable.

Specific compounds of matter and form are in a hierarchy of matter

and form; for what takes on a certain form will already have form at

some level. For example, a lump of bronze is matter with the

determinate form of bronze, and a bronze statue is matter with the

determinate form of bronze taking on the form of a statue. The same

bronze statue may be melted down and take on a new form, turning it

into a bronze bowl. With the progressive addition of form to matter we

can move “upward” from clay, to bricks, to walls, to house. That

matter and form are logically distinct is shown by the fact that we can

have the same form giving an instance of a kind of thing (a hammer)

but different matter (some metal, some wood), and have the same

matter (some metal) but a different form giving an instance of a kind of

thing (a hammer, a chisel).

These distinctions allow Aristotle to give an account of change. He

distinguishes two sorts of change:

(a’’) substantial change

(b’’) non-substantial change, or accidental change.

These mark the distinction between (a’’) cases where a new kind of

individual comes into being and (b’’) cases where the same kind of

individual thing persists in being through change. As a man moves

from being young to being old we have a case of non-substantial

change; the subject of change remains, through the change, the same

individual or instance of what kind of thing it is: a man. But when a

man dies, we have a case of substantial change—the individual

becomes a different kind of thing. What it is is something else: a mere

pile of flesh and bones. The form or essence of a thing X is a core set of

properties a, b, c, which are together necessary and sufficient for X to

be the kind of thing it is; that is, properties that jointly all and only

things of kind X have that thereby determine what they are. What

remains the same through substantial change (a’’) is the matter (a’)

which has lost one form (b’) and taken on another form. What remains

constant through non-substantial change (b’’) is the form (b’) or

essence, formulated in a definition, that gives those properties that

make a thing the kind of thing it is.

Another way of looking at this analysis of change is to make the

distinction between the essential properties ((2) above) of things and

the accidental properties ((3) above) of things; so these correspond to

the secondary substances and the non-substances respectively. The

essential properties are those properties that remain the same through

accidental change whereby an individual remains in existence as the

same kind of thing or what it is. Essential properties are the properties

which are necessary and sufficient for an individual to continue to be

42 Greek philosophy

an individual of a certain kind. The essential properties are given by

the true or real definition of the term designating the kind of thing an

individual is: so something is of kind X if, and only if, it has properties

a, b, c; and this is the same as giving its form. The form of a thing is its

essence given by a real definition, and this remains the same through

accidental change. Thus a man can be hairy and go bald; he can change

his blue shirt for a green shirt; but he still remains a man, since

hairiness is not part of the definition of man. What is part of the

essence of a man, given by the real definition of man, is the set of

properties common to all and only individual men that makes it

correct to include them under the term “man”. Thus the real definition

of man, revealing his essential nature, may be “mortal animal capable

of discourse”, which is definition by genus (animal) and difference by

species (capable of discourse). The essential nature, or form, of a

determinate kind is the residue of features which remain after the

differences between individuals of the same kind have been removed,

and we are left with a set of properties that all and only individuals of

that kind have in common; in that way we say what some thing is.

How individuals of the same natural kind are to be distinguished is

a difficult question. They cannot be distinguished by their kind, since

that is common to them. One suggestion is that they are distinguished

by their parcels of matter, which will be different parcels in each

individual. Another suggestion is that we should admit individual

essences as well as essences by kind. Later philosophers have said that

only a complete enumeration of attributes of a given individual,

denying any distinction between those that are essential and those that

are accidental, can give a satisfactory principle of individuation.

Generally it is held that, for a principle of individuation to guarantee

unique reference, some appeal to space, time and motion is required.

To complete Aristotle’s analysis of the nature of change, we have to

make the distinction between “actuality” and “potentiality”. When

matter takes on a certain form, there is contained within the nature of

the form not only what the actual form is at any given time, but also the

potential further actualizations. For example, an acorn has a certain

determinate actuality (actual state) at any given time; but it is also

potentially an oak tree. Thus a complete characterization of the form of

a thing—determining what kind of thing it is—will include a

description of various progressive stages of actualization, and the full

actualization towards which that kind of thing aims, which it contains

only potentially until it reaches that end point. So a specimen of a

certain kind will be a compound of matter and form, and the form will

include what is actualized at any given time, plus its future potential

states. This process is particularly obvious in the case of a living

organism; but what it means in the case of non-living things is less clear.

The point to be noted is that the form limits the way that a particular

kind of thing goes on; acorns do not develop into horses, but have a

Aristotle 43

certain natural course of development. An eye that is blind suffers from

“privation”, because it is not actualizing its potential; whereas to say

that a tree cannot see is not to say it suffers from privation, since to

actualize seeing is not a potential part of the form of a tree.

Natural kinds are divisions of nature herself, not divisions imposed

arbitrarily by us in language; the divisions are discovered, not created.

How many different natural kinds there are is a difficult question for

Aristotle, and his answers are not always consistent, (i) The criterion

sometimes emphasized for natural kinds is that they are those things

that persist through change. In this case it seems to make sense to

include artefacts like beds in the list of kinds; a bed remains a bed after

it has been painted green instead of blue. (ii) At other times the

criterion emphasized is that of independence from external causes.

Thus sometimes Aristotle includes in the natural world only things

which can reproduce themselves “after their kind”: horses naturally

beget other horses, whereas if you plant a bed, you do not get another

bed produced, it has to be made. Also bits of stuff like pieces of wood

are excluded from the list of natural kinds since they are

indeterminate—they are subject to destruction by degree; whereas it

makes no sense to say of a horse that it is more or less a horse—it is

either a horse or not a horse.

The explanation of change is, however, sometimes very unclear. This

is partly due to difficulties as to what natural kinds there actually are.

It is also due to the obscurity of the distinction between essential and

accidental properties. This produces the problem of distinguishing

substantial from accidental change. If, for example, we have a change

of property from f to g, it may not be clear if it is correct to say, “Xf has

become Xg” (an accidental change), or if it is correct to say, “Xf has

become Yg” (a substantial change). If sweet wine turns sour, it is

unclear whether it is correct to say that the sweet wine has become

sour wine (an accidental change), or that the wine has become vinegar

(a substantial change). How are we to distinguish a change in

substance, a change from “this so-and-so” to a different “this so-andso”,

from a merely accidental change in the same “this so-and-so”?

There is a danger that if the number of instances of secondary

substances increases, the explanatory power of explanations which

depend on referring to the kind of thing something is will be

diminished. If, at the limit, every change of properties involved a

change in kind, then we would be unable to explain the change in

terms of its being a consequence of the properties of the constant kind

of thing in question developing in its natural ways, according to its

form or nature.

The point that this talk of natural kinds is leading to is that the

explanation for why a thing is as it is can be derived from discovering

the kind of thing that it is and its connection with more general natural

kinds of things. The form of a thing is an intelligible form; it is

44 Greek philosophy

ultimately perceived not by the senses, but by the intellect or reason—

by intellectual intuition (nous). It is this reference to the kinds or sorts of

things there are in the world that is the basis for scientific knowledge

and explanations of the world.

Knowledge is knowledge of “causes”, and Aristotle gives four

senses to the notion of “cause”. It is important to see that “cause” here

has a wider connotation than our mechanical notion, and none of

Aristotle’s four senses really matches our use of the concept. When he

is referring to understanding the causes of things, he is concerned with

providing an answer to a “why” question: “Why is X as it is?” There

are various ways of answering this question through different

“becauses”. This is not at all mysterious if we consider the way we use

non-mechanical explanations every day. Question: “Why was Durham

Cathedral built?” Answer: “Because people wanted to praise God.” So

Aristotle distinguishes four “becauses” answering “Why is X as it is?”:

(a) Material

(b) Formal

(c) Efficient

(d) Final or Teleological

The (a) here refers to the matter or stuff (not necessarily physical stuff)

out of which X is made. (b) refers to what kind of thing X is; it is a “soand-so”.

(c) refers to the agent (not what the agent does) that brings X

about. (d) refers to what X is for, or what its goal or end state will be;

what its purpose is. If we take the case of a house, we can see that (a) is

the bricks out of which it is made; (b) is the kind of house it is

(Victorian style terrace); (c) is the men who built it; (d) points to its

purpose of providing shelter. It should be noted with reference to (c)

that causal links, or “becauses”, hold for Aristotle not between events,

but between things. Taken together, these four causes provide a

complete explanation for why X is as it is.

In the case of things with final causes, the formal and final causes

will be closely linked; in giving the form of something, it will be

necessary to refer in a definition to what that something is for. The use

of form and function in explanations allows us to see why something

can remain the same thing, even when certain changes are made to it.

If a green bed is painted blue, it remains the same as an individual

instance of bed, in that its form and final “becauses” are unchanged.

We can plainly see that formal and final explanations are more

obviously applicable to artefacts and living organisms than to

inanimate objects. Aristotle suggests that stones fall down because

their natural place—their natural final state spelt out in their form or

essence—is as near to the earth as possible. But we would hardly

regard this explanation as satisfactory today. There is the danger that

explanations derived from the kind of thing X is in this way become

uninformative and lead us to fail to seek the real internal causal

Aristotle 45

mechanisms that bring about a specific change. We have not

identifying the object before us as a clock. The explanations are at risk

of being uninformative because they become tautological: X is as it is

because of the real definition of X, and any counter-evidence is

immediately excluded because if a putative X is found to act in a way

contrary to its definition then it is not a case of X at all. We cannot

define a thing if we exclude its causal powers; we thereby risk circular

explanations if causal consequences are deduced from definitions.

All substantial change involves matter taking on a new form, which is,

in some way, passed on from an agent. In the case of a house, the efficient

cause operates by the form of the house that exists as an idea in the mind

of the builder being passed on to the matter of the house. In the case of

natural objects, the efficient cause is the natural parent in which the form

of the offspring is latent. This logically rules out both creation from

nothing—where there is no matter—and any possibility of Darwinian

evolution of the kinds of things there are, since the forms manifested in

natural kinds do not change in themselves. God is the supreme source of

all change; He transcends the world as pure form devoid of matter, fully

actualized, possessing no potential. God is not the creator of the world

out of nothing, but the “unmoved mover” in the sense of a final cause

which is the ultimate cause of whatever form the world has.

Knowledge proper requires that its objects must be both really

existing, and eternal and unchanging. If nothing in the sensible world

is eternal and unchanging, then it follows that knowledge of the

sensible world is not possible. If it is also the case that the sensible

world is the only really existing world, then knowledge is not possible

at all. If knowledge is possible, but it is accepted that the sensible

world is not eternal and unchanging, then knowledge must be of a

really existing transcendent supersensible world of eternal and

unchanging objects: the Forms or essences of Plato. If knowledge is

possible, but it is accepted that the sensible world is the only real

world, then knowledge must be of really existing eternal and

unchanging features of the sensible world: the forms or real kinds of

Aristotle. That is, if knowledge proper is possible, it must be the case

either that there is a world of eternal and unchanging real objects

beyond the sensible world (the position of Plato), or that there are

eternal and unchanging real features of the sensible world (the

position of Aristotle).

Aristotle holds that there is something about the sensible world that

is eternal and unchanging and graspable ultimately by the intellect and

is a suitable object for scientific knowledge: the natural kinds of things

there are and the relations between them. These natural kinds are

objective really existing features of the world, not mere arbitrary

conventional classifications imposed by us. The common-sense view of

the world is that it divides itself up into many distinct kinds or sorts of

individuals; and we have knowledge proper or scientific knowledge

46 Greek philosophy

(epist¯em¯e), as opposed to mere belief or opinion (doxa), of those

individuals through knowing the kind of thing an individual is. It is

natural or real kinds that are the proper objects of knowledge.

Aristotle made great contributions to logic, which he sees as the tool

(organon) of philosophy. Through the notion of the syllogism he sought

to identify all the valid forms of deductive reasoning. In fact there are

other forms of deductive reasoning that Aristotle does not consider.

Deductive logic is a vital tool of philosophy, and of inquiry generally,

in providing a way to get infallibly from true premises to true

conclusions. If the premises are true in a valid deductive argument,

then we know that it must be the case that the conclusion is true.

Aristotle introduced the important notion of variables—letters such as

A, B, and C—to stand for classes of things; this reveals that deductive

arguments are valid or invalid regardless of their content and in virtue

of their argument-form. For example:

This is a valid argument-form: an inference which would be valid

regardless of what classes of things are substituted for A, B, C.

Aristotle ideally sees knowledge as forming a system that is a

deductively connected body of truths. Scientific knowledge is

knowledge of causes: giving the reason why X is as it is, and must be as

it is. We have first to know what kind of thing X is, and then to show

why, given the kind of thing it is, X must be as it is. Thus knowledge of

some truth about X would consist of deducing the truth about X from

premises which we know are true, thereby proving by a valid deductive

argument that what we say is true about X is necessarily true of X.

Aristotle was aware of an important problem connected with this:

all knowledge cannot be a matter of providing a deductive proof or

demonstration, because this leads to an infinite regress of proofs: any

premises we suggested would themselves stand in need of further

proof. If the regress is infinite, then nothing can actually be proved,

and nothing therefore known. This leads Aristotle to the view that

there must be self-evident first principles or axioms that can be known

immediately by intellectual intuition (nous), which neither require nor

are capable of proof. The most general and firmest of these principles

is the law of non-contradiction, which in the Metaphysics Aristotle

states thus: “For the same thing to hold good and not to hold good

simultaneously of the same thing and in the same respect is

impossible.” This can also be expressed in a more modern way: “It is

not the case that both p and not-p”, where p can be any proposition.

This principle is presupposed in all rational thought; thus any attempt

to prove it by rational thought is hopelessly circular. We can, however,

Aristotle 47

prove it by rational thought is hopelessly circular. We can, however,

simply see intrinsically that it is a true principle.

Ideally the deductions of science would take place from the most

fundamental first principles; but, in fact, this is not possible; science

cannot proceed purely a priori, independently of experience, because the

most general first principles are too general for studying particular

kinds of things. The deductions of science are based on real forms (the

essences, real natures) of things and true universal principles (all As are

Bs) connecting these forms; and the process of apprehending both of

these is initiated by induction. We observe by sense-perception many

particulars of the same kind, and through reason or intellectual intuition

(nous) we “perceive” the form or essence of that kind of thing as a real

definition or concept given by genus and difference. We then form a

hierarchy of different degrees of generality, of kinds of things,

descending to infima specie: those specific kinds of things below which

there are no further kinds, but only individuals of a specific kind. Such a

species would be man, and above it, and including man, is the genus

animal. We also derive in the same way, by sense-perception and

intellectual intuition, universal principles logically connecting the forms

or essences. We are able to have knowledge proper since, by taking the

forms and universal principles together, we are able to deduce universal

certain necessary truths about the kind of things we are interested in.

In this way it is shown why things are as they are, and why they

must be as they are, and not otherwise. If a certain truth about the

world is the conclusion of a valid deductive argument whose premises

we know to be true, we have shown: (a) why that conclusion is a truth,

because it follows logically from known premises, and (b) that the

conclusion is a universal necessary truth, in virtue of the argument

being deductive. To follow a valid deductive argument from true

premises is to follow a causal connection in the world. We explain

some feature of the world by deducing it from the definition of the

kind of thing it is and from principles universally true of a general

kind of which it is a part.

We might ask why X is f. If we know the kind of thing X is—it is of

kind Y—and the universal principle that “all Ys are f”, then we can

deduce and explain, why X must be f.

For example: “Why does a horse suckle its young?”

48 Greek philosophy

The principle in the second line is what science seeks to use in

explanations, and it is known only by inductive observation of many

animals combined with the use of reason or the intellect. The first line

is known in the same way.

Science—knowledge in its highest sense—deals with universal

eternal necessary truths, not with particulars as particulars. The

forms or essences of kinds of things, and the universal principles

derived from the connection of those forms or essences, are the real

eternal unchanging intelligible aspects of the world. For science to

study what is real there must be kinds or sorts of things that mark

real, objective, fixed cleavages in the world, which are not the

imposition of human conventional classification. That they are real

is an assumption Aristotle makes on the basis of our common-sense

ways of talking about the world. Our explanations derive from the

ways that the vast plurality of things of certain real kinds behave,

given that their forms or essential natures determine the kinds they

fall into. The positing of such fixed intelligible forms is what makes

a scientific knowledge of nature possible, in the sense of knowing

universal necessary truths about universal necessary features of the

world. Scientific knowledge gives deductive proof that specific kinds

of things are necessarily as they are. The common principles of all

reasoning, plus known universal principles, plus knowledge of the

kind of specimen we have before us, together enable us to prove

necessary truths about that specimen. It is possible for us to have

scientific knowledge of the world, since the world can be

understood according to general principles and real definitions

which do not alter and are eternal, and which the intellect can

apprehend.

It must be noted that this means that science can deal with

particulars only in so far as it considers them instances of universals; it

considers only objective universal properties common to all and only

particulars of the same kind. Science is concerned not with what

makes a thing particular, but with what makes it an instance of a

general kind. Science can have as its object only genera, species or

universals—the specific defining form that individuals share—and not

particulars as such. Individuals are in the scientific sense unknowable;

in their unique particularity they are perhaps ineffable, since to talk of

them at all is to use common classifying terms which apply to other

individuals.

While we might grant that the proper principles or laws that

science aims to discover are universal in application, we do not

thereby have to agree they are necessary. The inductive inferences as

envisioned by Aristotle to derive general principles concerning kinds

of things would at best be known to be universally true. Even this is

clearly not possible if the number of kinds in the class to be

investigated is infinite. However, Aristotle thinks that such induction

Aristotle 49

produces evidence supporting universal necessary truths which

intellectual intuition apprehends as necessary. The problem is that

this tends to confuse contingent universal truths—which might be

supported, if not conclusively, by experience—with necessary

universal truths which are necessary just because their truth is

independent of all experience and which rely for their necessity only

on logic and the meaning of their terms. Aristotle relies on the

justification of intellectual perception—going beyond the limited

possibilities of experience—to establish finally the features of the

inmost nature or essence of things, the correctness of our real

definitions of those things, and the necessity of principles. But it is

not clear that an account of there being necessary truths depends on

the subjective intuitive self-evidence of some truths, rather than on

the purely objective logical form of such truths, such as the denial of

a necessary truth implying a contradiction. Moreover, if the necessity

of a truth is entirely a result of its denial implying a contradiction,

then it does not say anything about an actual world if the nature of

that world is not logically necessary but contingent; then truths

about that world cannot be known to be true merely by showing that

their denial implies a logical contradiction, because none of them

does.

Plato and Aristotle think that science should attain knowledge of

universal necessary truths. Aristotle thinks we can have scientific

knowledge of the sensible world because eternal unchanging forms

are immanent in the world of sensible objects. The sensible world

thus has two aspects: its sensible aspect, and its intelligible aspect

(the forms), and we can, through the intelligible aspect, know

necessary truths about the sensible world. That such provable

universal necessary truths—propositions whose falsity is

impossible—are restricted to mathematics and logic is now

something generally accepted to be the case. Plato, we might say, was

more aware of this point in thinking that if knowledge (epist¯em¯e) of

necessary truths were possible it must be of a supersensible world,

not of the empirical world. Plato thinks that the universal necessity

of the truths of highest forms of knowledge depends upon their being

about eternal transcendent supersensible objects beyond the natural

world: Forms, essences, or objective concepts. Whether such realism

is required to account for knowledge of universal necessary truths is

certainly disputable. It might be possible to account for necessary

truths without saying that they are about any world of real objects at

all, perhaps by saying that they are merely those propositions whose

denial implies a contradiction. Plato disagreed with Aristotle who

thought that knowledge, even in the highest sense of knowledge of

universal necessary truths, must be about aspects of the world of

sensible or empirical objects. The point at issue here is whether there

is such a thing as natural necessity: whether there are necessary

50 Greek philosophy

features and connections in the natural world expressible in

necessary truths, or whether such necessity is restricted to logical

truths which say nothing about the natural world, although they may

say something about a world of real objects apprehended by pure

intellectual thought beyond the natural world.

Aristotle 51

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