---
title: "Physics (Aristotle)"
chunk: 2/4
source: "https://en.wikipedia.org/wiki/Physics_(Aristotle)"
category: "reference"
tags: "science, encyclopedia"
date_saved: "2026-05-05T03:40:04.675125+00:00"
instance: "kb-cron"
---

 The necessary in nature, then, is plainly what we call by the name of matter, and the changes in it. Both causes must be stated by the physicist, but especially the end; for that is the cause of the matter, not vice versa; and the end is 'that for the sake of which', and the beginning starts from the definition or essence…
 
In chapter 3, Aristotle presents his theory of the four causes (material, efficient, formal, and final). Material cause explains what something is made of (for example, the wood of a house), formal cause explains the form which a thing follows to become that thing (the plans of an architect to build a house), efficient cause is the actual source of the change (the physical building of the house), and final cause is the intended purpose of the change (the final product of the house and its purpose as a shelter and home).
Of particular importance is the final cause or purpose (telos).  It is a common mistake to conceive of the four causes as additive or alternative forces pushing or pulling; in reality, all four are needed to explain (7.198a22-25). What we typically mean by cause in the modern scientific idiom is only a narrow part of what Aristotle means by efficient cause.
He contrasts purpose with the way in which "nature" does not work, chance (or luck), discussed in chapters 4, 5, and 6. (Chance working in the actions of humans is tuche and in unreasoning agents automaton.) Something happens by chance when all the lines of causality converge without that convergence being purposefully chosen, and produce a result similar to the teleologically caused one.
In chapters 7 through 9, Aristotle returns to the discussion of nature. With the enrichment of the preceding four chapters, he concludes that nature acts for an end, and he discusses the way that necessity is present in natural things. For Aristotle, the motion of natural things is determined from within them, while in the modern empirical sciences, motion is determined from without (more properly speaking: there is nothing to have an inside).

=== Book III (Γ; 200b–208a) ===
In order to understand "nature" as defined in the previous book, one must understand the terms of the definition. To understand motion, book III begins with the definition of change based on Aristotle's notions of potentiality and actuality. Change, he says, is the actualization of a thing's ability insofar as it is able.
The rest of the book (chapters 4-8) discusses the infinite (apeiron, the unlimited). He distinguishes between the infinite by addition and the infinite by division, and between the actually infinite and potentially infinite.  He argues against the actually infinite in any form, including infinite bodies, substances, and voids.  Aristotle here says the only type of infinity that exists is the potentially infinite.  Aristotle characterizes this as that which serves as "the matter for the completion of a magnitude and is potentially (but not actually) the completed whole" (207a22-23).  The infinite, lacking any form, is thereby unknowable.  Aristotle writes, "it is not what has nothing outside it that is infinite, but what always has something outside it" (6.206b33-207a1-2).

=== Book IV (Δ; 208a–223b) ===
Book IV discusses the preconditions of motion: place (topos, chapters 1-5), void (kenon, chapters 6-9), and time (khronos, chapters 10-14).  The book starts by distinguishing the various ways a thing can "be in" another. He likens place to an immobile container or vessel: "the innermost motionless boundary of what contains" is the primary place of a body (4.212a20). Unlike space, which is a volume co-existent with a body, place is a boundary or surface.
He teaches that, contrary to the Atomists and others, a void is not only unnecessary, but leads to contradictions, e.g., making locomotion impossible.
Time is a constant attribute of movements and, Aristotle thinks, does not exist on its own but is relative to the motions of things. Tony Roark describes Aristotle's view of time as follows:

Aristotle defines time as "a  number of motion with respect to the before and after" (Phys. 219b1–2), by which he intends to denote motion's susceptibility to division into undetached parts of arbitrary length, a property that it possesses both by virtue of its intrinsic nature and also by virtue of the capacities and activities of percipient souls. Motion is intrinsically indeterminate, but  perceptually determinable, with respect to its length. Acts of perception function as determiners; the result is determinate units of kinetic length, which is precisely what a temporal unit is.

=== Books V and VI (Ε: 224a–231a; Ζ: 231a–241b) ===
Books V and VI deal with how motion occurs. Book V classifies four species of movement, depending on where the opposites are located.  Movement categories include quantity (e.g. a change in dimensions, from great to small), quality (as for colors: from pale to dark), place (local movements generally go from up downwards and vice versa), or, more controversially, substance. In fact, substances do not have opposites, so it is inappropriate to say that something properly becomes, from not-man, man: generation and corruption are not kinesis in the full sense.
Book VI discusses how a changing thing can reach the opposite state, if it has to pass through infinite intermediate stages. It investigates by rational and logical arguments the notions of continuity and division, establishing that change—and, consequently, time and place—are not divisible into indivisible parts; they are not mathematically discrete but continuous, that is, infinitely divisible (in other words, that you cannot build up a continuum out of discrete or indivisible points or moments). Among other things, this implies that there can be no definite (indivisible) moment when a motion begins. This discussion, together with that of speed and the different behavior of the four different species of motion, eventually helps Aristotle answer the famous paradoxes of Zeno, which purport to show the absurdity of motion's existence.