> From "Topics" > ------------ > > " We must say, then, what a definition, a distinctive > property, a genus, and a coincident are. > > "A definition is an account that signifies the essence. > One provides either an account to replace a name or an > account to replace an account -- for it is also possible > to define some of the things signified by an account. > Those who merely provide a name, whatever it is, clearly > do not provide the definition of the thing, since every > definition is an account. Still, this sort of thing -- > for example, 'the fine is the fitting' [editor note: Aristotle's > reservation here is that replacing one word with another > is not really an account] -- should also be counted as > definitory. In the same way one should count as definitory > a question such as 'Are perception and knowledge the same > or different?'; for most of the discussion about definition > is occupied with whether things are the same or different. > Speaking without qualification, we may count as definitory > everything that falls under the same line of inquiry that > includes definition. > > "It is clear immediately that all things just mentioned > meet this condition. For if we are able to argue dialectically > that things are the same and that they are different, we > will in the same way be well supplied to take on > definitions; for once we have shown that two things > are not the same, we will have undermined the attempted > definition. The converse of this point, however, does > not hold; for showing that two things are the same is > not enough to establish a definition, whereas showing > that two things are not the same is enough to destroy a > definition."
Thanks for the reference, but I don't think it supports what you said, namely
In Aristotle, one finds the discussion that one can never define x=y. To be precise, he says that one can never prove a definition, but one can destroy a definition.
He does not say "one can never define x=y", since definition of equality is not discussed here, nor do I think this follows from anything he does explicitly say. And he also does not say "one can never prove a definition", but rather simply that showing two things are the same does not establish a definition. This means that one approach of establishing a definition does not work, but as far as I can tell, Aristotle *does* think one can establish definitions as correct, or else there would be little point (from his perspective) in discussing them.
Since pretty much every mathematical definition is stipulative, in any case (and at least from my perspective), this discussion of "establishing" a definition seems a bit off the mark, especially when applied to mathematics.
-- Jesse F. Hughes
" ... And I'm Michele Norris." -- Quincy P. Hughes