Since contraries are other in form, Footnote 1It appears that in this chapter (apart from 5, which may be a later addition) the terms εἶδος and γένος are used in a non-technical sense. Cf. Ross on Aristot. Met. 1058b 28. and the perishable
and imperishable
are contraries (for privation is a definite incapacity), the perishable
must be other in kind
than the imperishable.
But so far we have spoken only of the universal terms; and so it might appear to be unnecessary that anything perishable and imperishable should be other in form,
just as in the case of white and black.
For the same thing may be both at the same time, if it is a universal (e.g, man
may be both white and black); and it may still be both if it is a particular, for the same person may be white and black, although not at the same time. Yet white is contrary to black. But although some contraries
(e.g. those which we have just mentioned, and many others) can belong to certain things accidentally, others cannot; and this applies to the perishable
and the imperishable.
Nothing is accidentally perishable; for that which is accidental may not be applicable; but perishability is an attribute which applies necessarily when it is applicable at all. Otherwise one and the same thing will be imperishable as well as perishable, if it is possible for perishability not to apply to it.
Thus perishability must be either the substance or in the substance of every perishable thing. The same argument also applies to the imperishable; for both perishability and imperishability are attributes which are necessarily applicable. Hence the characteristics in respect of which and in direct consequence of which one thing is perishable and another imperishable are opposed; and therefore they must be other in kind.
Thus it is obvious that there cannot be Forms such as some thinkers maintain; for then there would be both a perishable and an imperishable man.
Footnote 2i.e., the individual man is perishable and the Idea of man imperishable; and these must be other in kind (γένει non-technical). But the Platonists hold that the Idea is the same in species as the particular. This is impossible if it is other in genus (γένει technical). Yet the Forms are said to be the same in species as the particulars, and not merely to share a common predicate with them; but things which are other in genus differ more widely than things which are other in species.