then clearly there
can be neither definition nor demonstration of individual sensible
things which perish are obscure to those who have knowledge of them
when they are removed from the sphere of their perception, and (b)
even though their formulae are preserved in the soul, there will no
longer be either definition or demonstration of them. Therefore in
cases relating to definition, when we are trying to define any
individual, we must not fail to realize that our definition may always
be upset; because it is impossible to define these things.
Nor, indeed, can any Idea be defined; for the Idea is an individual,
as they say, and separable; and the formula must consist of words, and
the man who is defining must not coin a word, because it would not be
comprehensible. But the words which are in use are common to all the
things which they denote; and so they must necessarily apply to
something else as well. E.g., if a man were to define you, he would
say that you are an animal which is lean or white or has some other
attribute, which will apply to something else as well.And if it should be said that
there is no reason why all the attributes separately should not belong
to several things, and yet in combination belong to this alone, we
must reply, (1.) that they also belong to both the elements; e.g.,
"two-footed animal" belongs both to "animal" and to "two-footed" (and
in the case of eternal elements this is even necessarily so; since
they are prior to the compound, and parts of it.Indeed they are also separable, if the
term "man" is separable—for either neither can be separable,
or both are so.
the genus will not exist apart from the species, or if it is so to
exist, so will the differentia); (2.) that "animal" and "two-footed"
are prior in being to "two-footed animal," and that which is prior to
something else is not destroyed together with it.
if the Ideas are composed of Ideas (for constituents are less
composite than that which they compose), still the elements of which
the Idea is composed (e.g. "animal" and "two-footed") will have to be
predicated of many particulars. Otherwise, how can they be known? For
there would be an Idea which cannot be predicated of more than one
thing. But this is not considered possible; every Idea is thought to
admit of participation.
Thus, as we have said,1
the impossibility of
defining individuals is hard to realize when we are dealing with
eternal entities, especially in the case of such as are unique, e.g.
the sun and moon. For people go wrong not only by including in the
definition attributes on whose removal it will still be
sun—e.g., "that which goes round the earth," or
"night-hidden " (for they suppose that if it stops or becomes
it will no longer be sun; but it is absurd that this
should be so, since "the sun "denotes a definite
substance)—they also mention attributes which may apply to
something else; e.g., if another thing with those attributes comes
into being, clearly it will be a sun. The formula, then, is general;