Physics 1.8

In Physics 1.8, Aristotle addresses Parmenides’ claim that “nothing that is can come to be or pass away”. Aristotle begins by presenting Parmenides proof:

“So they say that none of the things that are either come to be or passes out of
existence, because what comes to be must do so either from what is or from what
is not, both of with are impossible. For what is cannot come to be (because it is already),
and from what is not nothing could have come to be (because something must be
underlying).”

Next, Aristotle considers in what sense Parmenides and his followers are right, and the sense in which they “...were mislead in their search for truth by their inexperience.” Aristotle does this by showing that there are two ways to understand the expression ‘from what is’ and the expression ‘from what is not’.

In the case of ‘what is’, Aristotle distinguishes between ‘from what is’ and ‘what is acted on’. Here, Aristotle talks about how a doctor does not build a house qua doctor, but qua house builder. Aristotle then explains that, properly speaking, we talk about a doctor becoming or changing only when he is doing so qua doctor. In this way, when Parmenides speaks of coming to be from “what is not”, properly speaking, he refers to things becoming qua what is not. Aristotle thinks that in this sense, Parmenides is correct to say “things can’t come to be from what is not” but maintains that in the other, qualified sense, Parmenides is wrong. As we can speak of a doctor building a house outside his function, we can speak of what is coming to be from what is not. For example, a bird can come to be from what is not a bird (an egg), because the bird becomes a bird not qua what is not, but qua egg. Notice that here there is something underlying the change.

Using the same distinction between doctoring qua doctor, and doctoring qua house builder, Aristotle explains that Parmenides’ claim “nothing comes to be from what is” is right in cases where what is comes to be qua what is, but wrong in qualified cases. For example, Aristotle thinks an animal of a certain kind can come to be from an animal of a certain kind, and animals can come to be from animals. The dog Lassie (what is a dog) can come to be from the dog Rosy (what is a dog). Here, Lassie comes to be from a dog, but not qua dog, since the dog qualification caries over. In this way, what is can come to be from what is.

The main problem I have with Aristotle’s solution is that it seems to misconstrue Parmenides argument. When Parmenides talks about the impossibility of things to pass out of or into existence, he seems to be referring more to an original creation and not the generation and decay of existing things. In this way, he seems to be arguing that what exists always existed and always will exist. Parmenides might respond to Aristotle by saying that, while Aristotle might be correct about the use of man’s opinions, he has missed the point about what is or is not outside of it.