Physics Zeta (Z)


In Physics Z (Zeta) Aristotle addresses the question of whether motion is possible at all. This may seem a strange thing to do at this stage: Why is he doing it now, after giving an account of what motion and change are, and after seemingly describing various observable occurrences as if they were examples of really existent motions? That is, has he not been assuming all along that motion is possible?


One way to look at this would be to suggest that Aristotle's assumption that motion was possible is an assumption that he means to test: a hypothesis. We should also consider what he might mean by the terms translated as 'impossible', 'not possible', and 'cannot'. (The translation is not entirely consistent; but the terms used variously for all three are 'adunaton', literally 'unable', 'unable to do', 'unable to be done'; 'me endechesthai', literally 'not to admit of', 'not to allow [of]'; negatives of various conjugations of 'endechesthai'; and verb forms that indicate that something would not be accomplished or that a condition would not be met.) Interestingly, Aristotle does not come out and say that motion IS possible, or that he has proven that it is possible. Instead, he engages with several different arguments that he says try to make motion out to be impossible (or unaccomplishable or not allowable). What he concludes in each of these cases is that the arguments for the impossibility (or unallowability, etc.) of motion fail, or do not have to be construed as applying to the formulations of motion that Aristotle has given so far. This is not at all the same as proving that motion is possible or does exist. That is, to say that we do not have to take motion to be impossible (or unallowable, etc.); or even to say that motion is not impossible (or unallowable, etc.) is not to say that motion actually exists. Moreover, to say that motion does not have to be taken to be unallowable (i.e. to say that there is a coherent way of looking at motion that does not make it unallowable or unallowed), or even to say that motion is not unallowable (or not unallowed) is not necessarily to say that motion is possible.*


It might also help to consider the circumstances of Aristotle's discussion of the arguments against the possibility of motion. Certainly in a myth or a piece of creative writing, one might want to assert that motion was impossible (or that it was possible); and one might find great meaning of some sort in this assertion. One might find such meaning even if contradictions arose from the assertion, either in itself or when combined with other assertions or images; one might find such meaning even if one could not come up with a coherent definition of motion or a comprehensive view of it that took into account everything that it had to involve.
But Aristotle is not looking at what kind of assertions about motion make sense in poetry or myth; he is looking at assertions about motion as made within the context of "physics". That is, for physics to be able to be a "science", a body of demonstrable knowledge, A. had said, we think it should involve knowledge of causes and principles (reasons and sources for things). If it is to involve knowledge of causes and principles, the things physics studies should have causes and principles, and we should be able to recognize and to find these causes and principles. If one of those conditions does not hold - if there are no causes and principles in "nature" as we conceive of it, or if we cannot recognize or find them, or if we cannot tell whether there are causes or principles or whether we could recognize them as such, etc. - then we cannot claim that "physics" is a "science" in the sense in which A. says we usually think of "sciences" (bodies of demonstrable knowledge).**


Thus one thing that A. seems to be trying to do is to test the account of motion and its requisites and components (magnitude, time, place, continuity, succession, etc.) that he has given so far. He must test to see whether this account will fail to allow the possibility of causes and principles (and of recognizing and finding them). For example, if motion as he has described it must be impossible, then motion as he has described it is not going to have any causes and principles, because it is not going to happen (or cannot without contradiction be said to happen; and if there is a contradiction we will not be able to determine any causes and principles). On the other hand, if A. can show that his account of motion renders the arguments for the impossibility (unallowability, etc.) of motion invalid; or if he can show that under his account motion is not necessarily impossible (etc.); or if he can show that the arguments for the impossibility (etc.) of motion do not apply to his account; or is he can show that his account enables one to avoid those arguments without loss of anything crucial to physics; then at least with respect to this issue, he will have shown that it need not be impossible that there be discernible causes and principles in "nature", and that "physics" as "science" is not ruled out. Indeed, if we allow the possibility of paradoxes - such as situations where given 2 mutually exclusive options P and not-P, both P and not-P imply contradictions or incoherences - then even if we could show that it was not the case that motion was impossible (not just unallowable), that would not necessarily mean that we would be right (or non-contradictory or coherent) in saying that motion was possible. This is of course far from proving that there are discoverable causes and principles in "nature", or that the account of motion that he has given is right or true across all contexts or independent of our thought. But A. never said that he was going to prove those things.


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*Indeed, if we allow the possibility of paradoxes - such as situations where given 2 mutually exclusive options A and not-A, both A and not-A imply contradictions or incoherences - then even if we could show that it was not the case that motion was impossible (not just unallowable), that would not necessarily mean that we would be right (or non-contradictory or coherent) in saying that motion was possible.

**If we found that we could not or did not have a "science" of physics in this usual sense, we would either have to come up with a new conception of what should count as knowledge or as understanding in physics (or in general); or we would have to accept that as we are now, we do not gain knowledge of "nature" (of the things that we way grow and change, in so far as they are taken to grow and to change). The question of the viability and applicability of the cognizance-of-causes-and-principles model of knowledge or of "science" is explored implicitly in the Metaphysics.

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