in the case of secondary substances; the species 'man' and the
species 'ox' are not defined with reference to anything outside
themselves. Wood, again, is only relative in so far as it is some
one's property, not in so far as it is wood. It is plain, then,
that in the cases mentioned substance is not relative. But with
regard to some secondary substances there is a difference of
opinion; thus, such terms as 'head' and 'hand' are defined with
reference to that of which the things indicated are a part, and
so it comes about that these appear to have a relative character.
Indeed, if our definition of that which is relative was complete,
it is very difficult, if not impossible, to prove that no
substance is relative. If, however, our definition was not
complete, if those things only are properly called relative in
the case of which relation to an external object is a necessary
condition of existence, perhaps some explanation of the dilemma
may be found.

The former definition does indeed apply to all relatives, but the
fact that a thing is explained with reference to something else
does not make it essentially relative.

>From this it is plain that, if a man definitely apprehends a
relative thing, he will also definitely apprehend that to which
it is relative. Indeed this is self-evident: for if a man knows
that some particular thing is relative, assuming that we call
that a relative in the case of which relation to something is a
necessary condition of existence, he knows that also to which it
is related. For if he does not know at all that to which it is
related, he will not know whether or not it is relative. This is
clear, moreover, in particular instances. If a man knows