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Aristotle was a Greek philosopher who lived from 384 to 322 BC.
In his work Physics, he intends to establish the general principles of change that govern all natural bodies, living and inanimate, celestial and terrestrial. This includes all motion (change with respect to place), quantitative change (change with respect to size or number), qualitative change and substantial change (coming to be or passing away).
Empedocles
Elements and spheres
Aristotle divided his universe into:
Terrestrial spheres - which are corruptible and where humans live
Celestial spheres - which are moving but otherwise unchanging
Four classical elements make up everything in the terrestrial spheres: earth, air, fire and water. The heavens will be composed of a special weightless and incorruptible fifth element, known as aether. Aether has also been proposed as "quintessence" which means "fifth being." Heavy substances such as iron, and other metals were primarily composed of earth, with a small admixture of the other three elements. Other, lighter objects contain less earth.
Aristotle did not invent the four classical elements, however, it was Empedocles. It wasn't until the Scientific Revolution, that the concept of four elements was replaced by the concept of chemical elements.
Celestial spheres
For Aristotle, the Sun, Moon, planets and stars, are embedded in perfectly concentric crystal spheres. They rotate eternally at a fixed rate. These spheres are incapable of any change besides rotation. It is a terrestrial sphere of fire that accounts for heat, starlight and occasional meteorites. The lowest celestial sphere is the lunar sphere, the only celestial sphere that comes into contact with the sublunary orb's changeable and terrestrial matter.
These concentric crystal spheres that carry the Sun, Moon and stars, move eternally in an unchanging circular motion. Spheres are embedded within spheres to account for wandering stars. Neptune and Uranus are not incorporated into the model.
Aristotle wrote a work, the Physics in 8 books.
Book I
Book introduced Aristotle's approach to nature. This approach is based on principles, causes and elements. Before offering his views, he offers the views of others, such as Parmenides and Melissus, (of which you can read on my site elsewhere.) Aristotle's own view, which he expresses in Chapter 7 is that there are 3 principles: substances, opposites and privations.
Chapters 3 and 4 refute Parmenides, (who said that being was finite, immobile and like a perfect sphere) Melissus (who said being was immobile, unchanging and infinite) and Anaxagoras (who posited an infinite number of principles.)
Chapter 6 narrows the number of principles down to 2 or 3. He introduces the word matter in chapter 7, where he expresses his own views. This word was used to designate fundamental essence. Aristotle defines matter in chapter 9 of Book I.
Book II
Entities are 'natural' which are capable of starting to move, for example, growing, acquiring qualities, being born, dying, etc... Aristotle contrasts natural things with the artificial. Artificial things can move also, according to what they are made of, not according to what they are.
In chapter 3, Aristotle presents his theory on the four causes: material, efficient, formal and final. Material causes explains what things are made of. Formal causes explain the forms which a thing follows to become that thing. Efficient cause is the actual source of change. The final cause or purpose or telos is the intended purpose of the change.
All four are needed to explain a phenomenon.
For Aristotle, nature acts for an end. Necessity is present in natural things.
Book III
Chapters 4 through 8 discuss the infinite. Aristotle distinguishes between the infinite by addition and the infinite by division. He also distinguishes between the actually infinite and the potentially infinite. Aristotle argues against the actually infinite. The only type of infinity that exists is the potentially infinite.
The infinite, lacking any form, is unknowable.
Book IV
Book IV discusses the preconditions of motion.
Place (chapters 1-5) is likened to a container or vessel.
Void (chapters 6-9) which, contrary to Democritus and the Atomists, is unnecessary and generates contradictions. The void makes locomotion impossible.
Time (chapters 10-14) is a constant attribute of movements. It does not exist on its own, but is relative to the motion of things.
Books V and VI
Books V and VI describe how motion occurs. Book V classifies 4 species of movement.
Movement categories include:
1) Quantity - change in dimensions from great to small
2) Quality - as for colors: from pale to dark
3) Place
4) Substance
Substances do not have opposites.
Book VI, discusses how a changing thing can reach the opposite state.
Book VII
Book 7 discusses the relationship between the moved with its mover. Everything which moves is moved by another.
Book VIII
Book 8 occupies about a 1/4 of the entire of the Physics, discussing the time limits of the universe and the existence of a Prime Mover, which would be eternal, indivisible, without parts and without magnitude.
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