Preliminary Questions:
All of us are familiar with the words "logical" and "illogical." We speak, for instance, of a "logical" candidate, a "logical" procedure, and a "logical" choice. In these contexts the word "logical" means "in accordance with what one would reasonably expect in view of the events or circumstances." Again, using the word "logical" in a slightly different sense, we refer to a man whose thinking is orderly and consistent as a "logical" thinker and to an argument that clearly proves its conclusion as a "logical argument. On the other hand, we brand as "illogical" an action that is not called for by the circumstances, or a person whose thinking is disorderly and inconsistent, or an argument that does not prove its conclusion but is irrelevant, circular, or self-contradictory. You will notice that in every instance the words "logical" and "Illogical" refer to correct thinking--a choice is logical or illogical depending on whether or not it results from correct thinking; a person is logical or illogical depending on whether or not his thinking is correct; and an argument is logical or illogical depending on whether or not it expresses correct thinking.
Now, logic is the science and art of correct thinking. Just as chemistry investigates the laws governing the composition, relationships, and affinities of matter, and just as physics studies the laws of matter as endowed with motion and energy, so logic investigates, discovers, and applies the laws we must follow in order to think expeditiously and correctly. [Note: The method of logic, as well as the kind of knowledge it gives us, differs profoundly from that of chemistry and physics. In this paragraph we merely wish to call attention to its general area of investigation.]
In the definition of logic as the science and art of correct thinking the word "thinking" does not include absolutely all mental operations but only those mental operations (a) that are directed toward the attainment of truth and (b) by which we elaborate upon knowledge previously possessed. Reverie and daydreaming, for instance, are not thinking in the sense in which we are using the word here because they are not directed towards the attainment of truth. The operations by which we merely make things present to our minds are not thinking but a prerequisite of thinking, since they involve no elaboration upon knowledge previously possessed. Yet we do think when we analyze what has been made present to our minds--when we compare, classify, define, and divide. Similarly, the operation by which we merely accept a statement as true (like the simple assent to "2 + 2 = 4") are not thinking but a possible starting point of thought--logic acknowledges their existence and describes their nature, but cannot lay down laws to govern them. [Note: As an art, logic is concerned only with those mental operations over which it can exercise control; but as a science, it is also concerned with others. For instance, the consideration of induction belongs, at least to some extent, to the science of logic, but not to the art.] However, we do think when we draw out the implications of statements and "figure out" the connections between them. [Note: An implication is anything that is implied. Now in logic "to imply" means "to involve the truth or presence of." If two propositions are so related that if the first is true the second must also be true, the first is said to imply the second. The remark "The old skipper is sober today" hints, or suggests, that the skipper is not sober on some other days, but it does not logically imply this. It is possible for the skipper to be sober both today and on every other day.] Thinking, then, includes analysis, comparison, classification, definition, logical division, and so one, and especially the various kinds of inference. Logic studies these operations insofar as they are instruments of knowledge and means of attaining truth.
Logic is principally concerned with inference. It studies other operations of the mind chiefly (though not exclusively) because of their relationship to inference. Inference, in its broadest sense, signifies any process by which our minds proceed from one or more propositions (that is, from one or more statements in which anything whatsoever is affirmed or denied) to another proposition so related to the original propositions that if they are true it must also be true. Inference is expressed externally by oral or written argumentation, which is also called inference and of which the following syllogism is a typical example:
Every dog is an animal; but every hound is a dog; therefore every hound is an animal.
[Note: Examples about dogs, animals, and the like, are chosen because they are perfect illustrations of logical relationships. The fact that they are so commonplace increases their value as illustrations at this stage of our study. Examples with greater intrinsic interest would be likely to draw attention to themselves and distract us from the points they are meant to illustrate.]This example consists of three propositions so related that if the first two (the premises or antecedent) are true, the third proposition (the conclusion or consequent) must also be true. Our mind first accepts the first two propositions as true and then, on seeing the connection between them and the third proposition, asserts it as flowing from them. To establish general norms for making this passage from premises (or antecedent) to conclusion (or consequent) is the main task of logic.
Our thinking is correct when it conforms to the laws or rules investigated by logic. For instance, definition is correct if it conforms to the rules of definition; logical division is correct if it conforms to the rules; and the various kinds of inference are correct if they conform to their rules. Since very much of logic is a study of the conditions of correctness of thought, we cannot understand the meaning of "correct thinking" unless we first have studied logic.
Logic is a science--at least it is a science in the traditional Aristotelian and Thomistic sense of "science," although not quite in the same sense as physics, chemistry, anatomy, and so on. There is a tendency nowadays to restrict the word "science" to the so-called empirical or inductive sciences, such as physics, Hence, in spite of the fact that logic actually is a science, we do not ordinarily call a logic course a science course.
Science is knowledge, but not all knowledge is science. To rank as science, knowledge must fulfill several special requirements. Science is not mere opinion or hypothesis but certain and demonstrated knowledge; not a mere accumulation or aggregation of data but organized knowledge; not a bare statement of fact or a mere description of events but causal knowledge that tells why things are as they are. Now, logic is a science because it is certain and systematized knowledge of the principles governing correct thinking--it does not give us mere mechanical rules but gives us insight into why its rules must be as they are and cannot be otherwise.
Logic, as a science, investigates, discovers, expresses, systematizes, and demonstrates or explains the laws of correct thinking. But the actual application of these laws--for instance, to the construction and criticism of arguments--takes us out of the sphere of logic as a science and into the sphere of logic as an art.
Art gives facility, first, in reasoning and judging correctly about things to be made--such as statues, paintings, chairs, and syllogisms--and, secondly, in actually making them in accordance with the demands of reason.
Logic is an art because it guides man's reason so he can proceed with order and ease and without error in the constructive activity of making definitions, propositions, syllogisms, and so on. Indeed, logic is the "Art of Arts" (Ars Artium), or a sort of super-art, for it directs reason itself, which is the director of the other arts. Yet it is an art only in the secondary sense of the word, for its products (unlike those of sculpture, painting, building, and so on) are purely mental and imperceptible to the senses. Since logic perfects the intellect, which is the root of freedom (libertas), and since free men (liberi) should be pre-eminent in things of the mind, logic has traditionally been called a liberal art.
The laws and rules of logic are not arbitrary enactments that we submit to out of reverence for authority or because of long-established custom. We submit to these laws and rules only because we clearly see that they must be as they are--that is--the evidence compels us to submit. In a logic course there is no blind memorizing and no merely mechanical application of rules that have been learned by rote. The student should not be satisfied with anything short of a thorough understanding of all the fundamentals of logic.
All of us are logicians by nature--at least to some extent! We must not suppose that we know nothing at all about logic before we have made a formal study of it. Simply because we are rational beings, we spontaneously know the more general laws of correct thinking and are necessarily subject to them. Just as the law of gravitation was operative before Newton formulated it, so, too, men followed the more general laws of thought before Aristotle (384-322 BCE) and other logicians put them into words. But for a detailed knowledge of these laws and for skill in applying them prolonged study is absolutely necessary.
Logic does not give us knowledge of the real world, at least not directly, but only of certain aspects of our thought. It does not consider real things but certain aspects of our knowledge of real things. Hence (a) logic, inasmuch as it is a mere tool of reason, makes no direct contribution to the content of our thought and (b) logic presupposes means of attaining truth over which it has no control.
Students of logic are sometimes disappointed on being told that a logician as such does not even know enough to come in out of the rain or that he does not even know that a dog is an animal. As a man, of course, he knows these things, but not as a logician because they lie outside the field of logic. The sole object of logic is certain aspects of our thought--it considers concepts, propositions, arguments; the subject-predicate relationship; the relationship of the minor, middle, and major terms of a syllogism; the logical sequence of propositions; and so on. It does not give us any knowledge at all of real things except insofar as it is a tool of reason and thereby guides us in our thoughts about things and aids the other sciences in attaining truth.
Another limit of logic is suggested by the definition of "thinking." We defined "thinking" as those mental operations (a) that are directed toward the attainment of truth and (b) by which we elaborate upon knowledge previously possessed. Since we cannot think unless we first have something in our minds to think about, logic presupposes means of attaining truth over which it has no control. It assumes that we accept many truths independently of logic and logical procedures.
EXPERIENCE. The immediate data of experience are not subject to the control of logic. Many things are immediately evident to us because we experience them--we see, touch, and handle them. The fact that we exist, too, is immediately evident to us because we experience ourselves knowing other things, feeling, willing, and so on. [Note: Gabriel Marcel (1889-1973) correctly insisted that "I am, therefore I think" against Rene Descartes (1596-1650) who claimed "I think, therefore I am."]
INSIGHT INTO PRINCIPLES. Truths like the principle of contradiction ("A thing cannot be and not be in the same respect") and simple relationships of numbers (such as "2 + 2 = 4") impose themselves on our minds because by insight into concrete exemplifications of these truths we clearly understand that they must be true. The basic principles of logic and metaphysics are of this sort--we cannot, strictly speaking, prove them: we can only see them when we inspect examples in which they are illustrated [Note: These principles are grasped by so-called intellective induction]. Now, in the acceptance of truths that are immediately evident (whether they are immediate data of experience or principles grasped by insight into examples), there is no movement of thought from one thing to another, no elaboration of knowledge previously possessed, but only a simple assent to truth. Hence, such acceptance of truth is not "thinking" in the sense in which we understand the word here and therefore lies outside the control of logic.
AUTHORITY. We accept many statements merely because an authority we consider reliable has proposed them to us as true. Reliance on authority is our reason for accepting much of what we read in the newspapers and hear over the radio and in conversation. Indeed, reliance on authority is often the only possible way of getting information about things that we have not witnessed ourselves. It is also why we accept many of the conclusions of science: no one--not even a great scientist--can examine all the data of science and test the validity of all its conclusions for himself. Reliance on authority is also the reason for accepting the dogmas of revealed religion.
Now, logic has no direct bearing on the acceptance of statements on authority. It can, however, have an indirect bearing. First, it can sometimes help us make a critical examination of the reasons for accepting an authority as worthy of credence. For instance, logic can help us discover inconsistencies of thought; and we will rightly be suspicious of the reliability of an authority (a newspaper columnist, editorialist, historian, and so on) if he makes statements that we find to be either self-contradictory or inconsistent with what we already know to be true. Secondly, logic can guide us when we elaborate on what an authority has proposed to us as true. Thus, authority, just as experience and insight into principles, can supply us with things to think about--that is, with matter that we can subject to logical analysis and use as the starting points of inference.
We shall now give a brief answer to the question, Why should we study logic? When you begin a new subject it is helpful to consider the benefits to be gained from its study; and later, as the course progresses, it is often highly advantageous to reflect on whether, and to what extent, these benefits are being attained.
The specific purpose of logic is expressed in its definition by the words "correct thinking." Logic gives us norms for recognizing correct or good thinking, as well as incorrect or bad thinking, and develops in us a habit of analyzing our thought, of distinguishing carefully between our evidence and our conclusions, and of adverting to the structure of our arguments. By familiarizing us with both correct and incorrect procedures, it helps us know for certain whether or not our evidence justifies our conclusions, and teaches us what to look for in order to test the validity of arguments.
How often it happens that we have a vague suspicion that something is wrong with an argument or even know for certain that it is invalid and yet cannot state precisely what is wrong with it! The study of logic will enable us to pinpoint the defects of faulty arguments--to explain exactly what is wrong with them and to give the flaw a name.
Logic, then, has the very practical purpose of helping us think with order and ease and without error. It should enable us to discover defects in the thinking of others and to avoid defects in our own thinking.
The strictly philosophical portions of logic, which show the connection of the laws of logic with the basic principles underlying them should give us a deep understanding of the conditions of sound argument and therefore a profound trust in the competence of the human mind, as well as great mental satisfaction.
Another reason for studying logic is that its study is an apt introduction to philosophy.
A BRANCH OF PHILOSOPHY. In the first place, logic is a branch of philosophy at least to the extent that many parts of the science of logic are genuinely philosophical. Hence, logic introduces us to philosophy by inviting (or even compelling) us to philosophize. It introduces us to the abstract thinking of philosophy and familiarizes us with some of its technical terminology. (Now we must not be surprised that philosophy has a technical vocabulary; it is just as impossible to talk about philosophy without at least some knowledged of its technical vocabulary as it is to talk about baseball, football, and tennis without at least a little knowledge of their technical vocabularies.) Indeed, logic is a veritable storehouse of philosophical terms, and by acquainting us with them it prepares us to read philosophical writings intelligently. [Note: Sometimes logic is contrasted with philosophy. But when this is done the word "philosophy" is used in a narrow sense as synonymous with "metaphysics," which is philosophy par excellence.]
A TOOL OF PHILOSOPHY. Logic is a tool of philosophy just as it is a tool of reason in general. Much of what was said about the specific purpose of logic (under a) is applicable in a special way to the use made of logic throughout philosophy.
AN INTRODUCTION TO PROBLEMS OF PHILOSOPHY. Logic also introduces us to philosophy by introducing us to various philosophical problems that are considered from one point of view in logic and from other points of view in other branches of philosophy. The so-called problem of universals, for instance, has a logical aspect and therefore belongs to logic; but it likewise pervades much of metaphysics, epistemology, and even psychology. The consideration of principles underlying correct thinking necessarily leads us to principles of metaphysics, and so on. An acquaintance with these problems from the point of view of logic will at once whet our philosophical appetites with a real hunger for their complete solution and fill out our philosophical background so that when the complete solution is given us we will be the better prepared to understanding it.
There is also a very cogent historical reason for studying logic. Logic has been an important subject of study for more than 2400 years. From before the time of Aristotle (d. 322 B.C.E.) down to our own day, the study of logic, and especially of Aristotelian logic, has remained an important part of a liberal education. Even when other branches of philosophy fell into decadence and nearly passed out of existence, as in the so-called Dark Ages, logic continued to be taught. It has had a strong influence on Western thought, and many of its once technical terms have passed into everyday language.
Now the mere fact that a subject has flourished for over 2400 years and still continues to be taught gives us a very strong presumption in favor of its being worthwhile.
The definition of logic as the science and art of correct thinking defines logic by stating its proximate end or purpose. Later, we shall consider logic from another point of view and define it in terms of its formal object. For an adequate understanding of the nature of logic we must consider both its purpose and its formal object. It would be impractical, however, to treat of its formal object at this stage of our study.