(or "Physica", or "Physicae Auscultationes" meaning "lessons") is a key text in the philosophy of Aristotle . It inaugurates, in the current Andronichean order, the long series of Aristotle's physical, cosmological and biological works, and is preliminar to them. This collection of treatises or lessons deals with theoretical, methodological, philosophical concerns, rather than physical theories or contents of particular investigations. It sets the bases for the scientist to study the world subject to change, and change, or movement, or motion (''kinesis'') is one of the chief topics of the work.
The Physics is composed of eight books.
- discusses the scientist's approach to nature and the world of changing things: remarks on method, a discussion of how some ancestors viewed nature, and the basic elements of change: a property (''privation''), which is overcome by its opposite (''form''), both of them belonging to a subject (''substrate'') which is not altered in the change.
- introduces the term "nature" (Gr. ''physis'') as "the ability of setting itself in motion". Thus, those entities are natural which are capable of starting to move, e.g. growing, acquiring qualities, displacing themselves, and finally being born and dying. (Artificial entities are not born, nor can they grow or feed themselves). Here is also where Aristotle presents his theory of the Four Causes ; the particular importance of the ''final'' cause, the purpose ('' Telos ''), in nature, is stressed and contrasted with the way in which nature doesn't usually work, chance (and luck). Something happens by chance when all the stages, which would usually lead to it, ''coincidentally'' sum without being purposefully chosen, and produce a result similar to the Teleologically caused one. This applies in human decisions as well as in nature.
- and IV are akin in interest and probably formed a textual whole, defining the preconditions of motion. Bk. III begins with a very controversial definition of change involving the metaphysical notions of Potentiality And Actuality : it is the passage from being something ''potentially'' and becoming it ''actually'', and this is the structure every natural phenomenon can be reduced to. The rest of the book is a treatment of infinity, a property which no physical magnitude can have, and which (both by addition and by division) only exists "upon reflection".
- prosecutes discussing the preconditions of motion with treating place (''topos''), and the various ways a thing can "be in" another (bodies can occupy place without us having to accept the existence of void); and time (''khronos''), which is a constant attribute of movements and which, Aristotle thinks, doesn't exist on its own but is relative to the things. The relationship among time, motion and the human soul is not univocally settled down: time is defined as "the number of movement in respect of ''before'' and ''after''", so it cannot exist without that; but it is also said that it is the soul, capable of measuring the movement, which makes there be time.
- and VI deal with ''how'' motion works. Bk. V classifies four species of movement, depending on where are the opposites located: in the categories of 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.
- discusses how a changing thing can reach the opposite state, if it has to pass through the infinite intermediate stages. It investigates by rational and logical arguments the notions of ''continuity'' and ''division'', establishing that change -and time, and place, consequently- are not divisible into indivisible parts; they are not mathematically on his claim that the existence of motion is absurd, by replying to his Paradoxes .
- briefly deals with the relationship of the moved to his mover, which Aristotle describes in substantial divergence with ''' Plato ''''s theory of the soul as capable of setting itself in motion ('' Laws '' book X, '' Phaedrus '', '' Phaedo ''): everything which moves, is moved by other. He then tries to commensure the species of motion and their speeds, with the local change (locomotion, ''phorà'') as the most fundamental to which the others can be reduced.
- (which occupies almost a fourth of the entire ''Physics'', and probably constituted originally an independent course of lessons) discusses two main topics, though with a wide deployment of arguments: the time limits of the universe, and the existence of a ) by love and aspiration.
Book VII has also come to us in an alternative version, not included in the Bekker Edition .
A very good introductory work on the ''Physics'' is:
''Die Aristotelische Physik'', W. Wieland, 1962, 2nd revised edition 1970.
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