Physics by Aristotle

First transcribed:Physica, second Athenian period, 335-323 b.c.e. (English translation, 1812)

Type of Philosophy: Metaphysics, philosophy of science

Context

In modern times, with the growth of natural science, most of the topics treated by Aristotle in Physics would be classified as metaphysics. The collection of treatises bearing that name has come to stand for any speculative question concerning first principles, and in that light the topics of the Physics are closer to metaphysics than to modern questions of physics. Aristotle begins by considering the number and character of the first principles of nature, and he goes on to argue against Parmenides’ speculative theories. Nevertheless, the topics here considered do concern first principles of the physical world, and the work is still a classic in its grasp of issues fundamental to all physical inquiry.

Book 1 opens by stating that it is first principles that one must come to know. To know a thing means to grasp its first principles and to have carried the analysis out to the simplest elements. One proceeds from things more obvious and knowable to one to those principles more clear and knowable by nature. The first question is whether the first principles involved are one or more than one. As a physicist, Aristotle takes it for granted that the things that exist by nature are, either all or some of them, in motion. Speculative theories to the contrary (the idea of “Being as one and motionless”), he dismisses.

One of the famous questions of the Physics now begins to develop: whether there is an actual infinite in the category of quantity. The infinite qua infinite, Aristotle firmly believed, is unknowable; it is primarily this epistemological difficulty that plagues Aristotle about the infinite. The principles of physical nature cannot be either one or innumerable. A finite number is sufficient, and an infinite number would be unknowable.

In dealing with coming into being and change, Aristotle uses potentiality and actuality as explanatory concepts. What desires form is matter, and matter is the origin of potentiality and form the symbol of actuality. “Matter” Aristotle defines as the primary substratum of each thing, from which it comes to be without qualification and which persists in the result. “Nature” Aristotle defines as a source or cause of being moved and of being at rest in that to which it belongs primarily. However, no thing has in itself the source of its own production.

In book 2, Aristotle returns to the basic problems of physics. Form is more nearly nature than matter, for a thing is more properly said to be when it has attained fulfillment (fully formed) than when it exists potentially. However, one also speaks of a thing’s nature as being manifest in the process of growth by which its nature is attained. Aristotle makes a distinction between physics and mathematics. Physical objects contain surfaces, volumes, lines, and points (the subject matter of mathematics), but the mathematician does not treat them as the limits of a physical body. He separates them, for in thought they are separable from motion. The objects of physics are less separable than those of mathematics. Such things are neither independent of matter nor definable in terms of matter only. Of course, matter is a relative term; to each form there corresponds a special matter.

Causes

Aristotle changes topics again, this time to define the four types of causes:

1. that out of which a thing comes to be, the matter, or material cause

2. the form or the archetype, the formal cause

3. the end, or purpose, the final cause

4. the primary source of change or coming to rest, the efficient cause

Aristotle adds chance and spontaneity to these four causes, an addition that is often overlooked because these latter two causes are not amenable to knowledge, and yet any complete account must include them. Chance is unstable and is thus inscrutable.

Nature belongs to the class of causes that act for the sake of something, and therefore it is amenable to intelligence. Those things are natural that, by a continuous movement originated by an internal principle, arrive at some completion. Nature is a cause, a cause that operates for a purpose. Nature is to be defined as a “principle of motion and change.” The fulfillment of what exists potentially, insofar as it exists potentially, is motion. It is not absurd that the actualization of one thing should be in another.

Place and Time

In book 3, Aristotle turns to the problem of the existence of an infinite, and he readily admits that many contradictions result whether or not one supposes an infinite to exist. Is there a sensible magnitude that is infinite? This is the physicist’s problem. Aristotle begins by assuming that number is a numberable quantity. Having concluded that the sensible infinite cannot exist actually, Aristotle goes on to discuss whether it might have potential existence. The infinite has turned out to be the contrary of what is said to be. The infinite is potential, never actual. Its infinity is not a permanent actuality but consists in a process of coming to be, like time and the number of time.

Place is the concept under consideration in book 4. Now if place is what primarily contains each body, it would be a limit. The place of a thing would be its form. However, the place of a thing is neither a part nor a state of it but is separable from it. Place would not have been thought of if there had not been a special kind of motion; namely, that with respect to place. Aristotle concludes that the innermost motionless boundary of what contains is place. Furthermore, places are coincident with things, for boundaries are coincident with things and also with places.

After place, Aristotle begins his famous consideration of time. Aristotle considers it evident that time is not movement nor is it independent of movement. People perceive movement and time together. Time, he concludes, is just this—the number of motion in respect to before and after. Time, then, is a kind of number. Just as motion is a perpetual succession, so also is time. Time and movement define each other.

It is obvious, then, that things that always are cannot be in time; time by its nature is the cause of decay because change removes what now is. Yet because time is the measure of motion, it is also indirectly the measure of rest. In conclusion one asks: Will time fail? Surely not, if motion always exists. Time has being in the same way that motion does. Every change and everything that moves is in time.

Motion

In book 5, Aristotle begins to move the argument from motion toward the motionless. The goal of motion, he insists, is really immovability. Only change from subject to subject is motion, and there are three kinds of change: qualitative, quantitative, and local. In respect to substance, there is no motion, because substance has no contrary among things that are. Change is not a subject. There must be a substratum underlying all processes of becoming and changing.

Book 7 begins by asserting that everything that exists is in motion and must be moved by something. However, this series cannot go on to infinity. Therefore, the series must come to an end, and there must be a first movement and a first moved. This is Aristotle’s argument for the existence of an Unmoved, Prime, or First Mover from the very nature of motion itself. A great deal of the force of the argument derives from the requirements of Aristotelian knowledge. Knowing and understanding imply that the intellect has reached a state of rest and has come to a standstill, and this can be so only if the mind can find a satisfactory explanation for the origin of motion. Nevertheless, time is uncreated and motion is eternal. There must always be time.

It is clear that there never was a time when motion did not exist and that the time will never come when motion will not be present. There must be three things: the moved, the movement, and the instrument of motion. However, the series must stop somewhere. Because the kinds of motion are limited, there will be an end to the series. Consequently, the first thing that is in motion will derive its motion either from something that is at rest or is from itself. However, that which is itself independently a cause is always prior as a cause, and this argues for the source of motion in something itself at rest. That which primarily imparts motion is itself unmoved.

There must necessarily be some such thing, which, while it has the capacity of moving something else, is itself unmoved and exempt from all change—this is the crux of Aristotle’s argument. Because motion is eternal, that which first causes movement will also be eternal. It is sufficient, he feels, to assume only one movement, the first of unmoved things; and this will be eternal and the principle of motion to everything else. The first movement must be something that is one and eternal. If the first principle is permanent, the universe must also be permanent because it is continuous with the first principle. However, motion is of two kinds. Some things are moved by an eternal unmoved movement and are therefore always in motion. Other things are moved by an agent itself in motion and changing, and so they, too, change their motion.

Locomotion, Aristotle feels, is the primary motion. Yet it is possible that there should be an infinite motion that is single and continuous. This motion is rotary motion, since rectilinear motion cannot be continuous. There cannot be a continuous rectilinear motion that is eternal. On the other hand, in motion on a circular line are found singleness and continuity. Rotation is the primary locomotion. Every locomotion is either rotary or rectilinear or a compound of the two. Rotary motion can be eternal, and therefore, it is prior as motion.

Aristotle concludes that there always was and always will be motion throughout all time. The first movement of this eternal motion is unmoved, and rotary motion alone can be eternal and is primary. If the series comes to an end, a point is reached at which motion is imparted by something that is unmoved. The only continuous motion, then, is that which is caused by the Unmoved Mover, and such a First or Unmoved Mover cannot have any magnitude, is indivisible, and is without parts.

Aristotle’s conclusion to Physics is really only an introduction to the repetition and extension of some of the arguments later to appear in the book of edited writings entitled Metaphysica (second Athenian period, 335-323 b.c.e.; Metaphysics, 1801). Yet in this preliminary book most of the crucial concepts concerning physical nature are given a basic definition. The first principles of physics have been enumerated and defined. All that lies beyond physics is metaphysics.

Principal Ideas Advanced

•To know a thing involves understanding first principles.

•Matter is potentiality, form is actuality; to each form there corresponds a special matter.

•There are four types of causes: the material cause (matter); the formal cause (the kind); the final cause (the purpose); and the efficient cause (that which initiates change); in addition, change and spontaneity are kinds of causes.

•Nature, defined as a principle of motion and change, is a cause that operates for a purpose.

•The infinite is potential, never actual.

•Place is the innermost motionless boundary of that which contains; time is the number of motion in respect to before and after.

•There are three kinds of change: qualitative, quantitative, and local.

•There must be an Unmoved Mover that by eternal rotary motion imparts motion to all things.

Bibliography

Ackrill, J. L. Essays on Plato and Aristotle. New York: Oxford University Press, 1997. This work contains important and insightful reflections on two of the most influential thinkers in Western philosophy.

Adler, Mortimer J. Aristotle for Everybody: Difficult Thought Made Easy. New York: Scribner’s 1997. A reliable interpreter provides an account that introduces Aristotle’s thought in accessible fashion.

Bar On, Bat-Ami, ed. Engendering Origins: Critical Feminist Readings in Plato and Aristotle. Albany: State University of New York Press, 1994. Feminist perspectives are brought to bear on Aristotle’s philosophy in significant ways.

Barnes, Jonathan. Aristotle. New York: Oxford University Press, 1982. A reliable study designed for readers who want an introduction to Aristotle’s thought.

Barnes, Jonathan, ed. The Cambridge Companion to Aristotle. New York: Cambridge University Press, 1995. An excellent guide to Aristotle’s thought, which features significant essays on major aspects of his work.

Broadie, Sarah. Ethics with Aristotle. New York: Oxford University Press, 1991. This carefully done book concentrates on Aristotle’s ethical theory and its implications.

Brumbaugh, Robert S. The Philosophers of Greece. Albany: State University of New York Press, 1981. An introductory study that discusses Aristotle’s philosophy within the larger context of the Greek world.

Cooper, John M. Reason and Human Good in Aristotle. Cambridge, Mass.: Harvard University Press, 1975. Cooper’s book is a study of the “theoretical backbone” of Aristotle’s moral philosophy—his theories of practical reasoning and of human happiness.

Copleston, Frederick. A History of Philosophy: Greece and Rome. Garden City, N.Y.: Doubleday, 1962. A leading scholar of Western philosophy discusses Aristotle’s life as well as his logic, metaphysics, ethics, politics, and aesthetics.

Edel, Abraham. Aristotle and His Philosophy. New Brunswick, N.J.: Transaction Books, 1996. A careful and helpful study by a veteran interpreter of Western thought.

Ferguson, John. Aristotle. Boston: Twayne, 1972. Assisting the general reader in the study of Aristotle’s works, this book discusses Aristotle’s life and his views about nature and psychology and also offers perspectives on Aristotle’s lasting influence.

Hughes, Gerard J. Aristotle on Ethics. New York: Routledge, 2001. A fresh introduction to the philosopher, refining the translation of Arstotle’s terms with a sensitivity to context.

Husain, Martha. Ontology and the Art of Tragedy: An Approach to Aristotle’s Poetics. Albany: State University of New York, 2001. An examination of the Poetics using Metaphysics as a touchstone. Husain demonstrates the relationship between the works and how the latter illuminates the former.

Jones, W. T. A History of Western Philosophy: The Classical Mind. New York: Harcourt, Brace and World, 1969. Combines historical interpretation of Aristotle’s far-reaching thought with relevant readings from Aristotle’s writings.

Kenny, Anthony. Aristotle on the Perfect Life. New York: Cambridge University Press, 1980. This work focuses on Aristotle’s views about human nature, ethics, and politics.

Lear, Jonathan. Aristotle and Logical Theory. New York: Cambridge University Press, 1980. A detailed study of Aristotle’s views on logic and their continuing significance for understanding human reasoning.

McLeisch, Kenneth. Aristotle. New York: Routledge, 1999. An excellent biographical introduction to the thoughts of the philosopher, clearly presented and requiring no special background. Bibliography.

Mulgan, R. G. Aristotle’s Political Theory: An Introduction for Students of Political Theory. Oxford: Clarendon Press, 1977. Seeks to bring the major themes and arguments in Aristotle’s political theory into sharper focus than they appear in the Politics itself.

Randall, John Herman, Jr. Aristotle. New York: Columbia University Press, 1960. An older but reliable survey of Aristotle’s philosophy.

Robinson, Timothy A. Aristotle in Outline. Indianapolis, Ind.: Hackett, 1995. Accessible to beginning students, this clearly written survey covers Aristotle’s full range of thought.

Rorty, Amélie Oksenberg, ed. Essays on Aristotle’s ‘Ethics.’ Berkeley: University of California Press, 1981. An important collection of essays that concentrates on various facets of Aristotle’s influential moral philosophy.

Smith, Thomas W. Revaluing “Ethics”: Aristotle’s Dialectical Pedagogy. Albany: State University of New York, 2001. Smith argues for a reading of Ethics, not as a moral guidebook, but as a pedagogy—course work—for developing a questioning mind.

Strathern, Paul. Aristotle in Ninety Minutes. Chicago: Ivan Dee, 1996. A brief, easily accessible, introductory overview of Aristotle’s philosophy.