The Complete Aristotle (eng.)

each perishable thing.
The same account holds good for imperishableness also; for both are
attributes which are present of necessity. The characteristics,
then, in respect of which and in direct consequence of which one
thing is perishable and another imperishable, are opposite, so that
the things must be different in kind.
    Evidently, then, there cannot be Forms such as some maintain,
for then one man would be perishable and another imperishable. Yet
the Forms are said to be the same in form with the individuals and
not merely to have the same name; but things which differ in kind
are farther apart than those which differ in form.

Book XI
    Translated by W. D. Ross
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    div id="section119" class="section" title="1">
1
    That Wisdom is a science of first principles is evident from the
introductory chapters, in which we have raised objections to the
statements of others about the first principles; but one might ask
the question whether Wisdom is to be conceived as one science or as
several. If as one, it may be objected that one science always
deals with contraries, but the first principles are not contrary.
If it is not one, what sort of sciences are those with which it is
to be identified?
    Further, is it the business of one science, or of more than one,
to examine the first principles of demonstration? If of one, why of
this rather than of any other? If of more, what sort of sciences
must these be said to be?
    Further, does Wisdom investigate all substances or not? If not
all, it is hard to say which; but if, being one, it investigates
them all, it is doubtful how the same science can embrace several
subject-matters.
    Further, does it deal with substances only or also with their
attributes? If in the case of attributes demonstration is possible,
in that of substances it is not. But if the two sciences are
different, what is each of them and which is Wisdom? If we think of
it as demonstrative, the science of the attributes is Wisdom, but
if as dealing with what is primary, the science of substances
claims the tide.
    But again the science we are looking for must not be supposed to
deal with the causes which have been mentioned in the Physics. For
(A) it does not deal with the final cause (for that is the nature
of the good, and this is found in the field of action and movement;
and it is the first mover-for that is the nature of the end-but in
the case of things unmovable there is nothing that moved them
first), and (B) in general it is hard to say whether perchance the
science we are now looking for deals with perceptible substances or
not with them, but with certain others. If with others, it must
deal either with the Forms or with the objects of mathematics. Now
(a) evidently the Forms do not exist. (But it is hard to say, even
if one suppose them to exist, why in the world the same is not true
of the other things of which there are Forms, as of the objects of
mathematics. I mean that these thinkers place the objects of
mathematics between the Forms and perceptible things, as a kind of
third set of things apart both from the Forms and from the things
in this world; but there is not a third man or horse besides the
ideal and the individuals. If on the other hand it is not as they
say, with what sort of things must the mathematician be supposed to
deal? Certainly not with the things in this world; for none of
these is the sort of thing which the mathematical sciences demand.)
Nor (b) does the science which we are now seeking treat of the
objects of mathematics; for none of them can exist separately. But
again it does not deal with perceptible substances; for they are
perishable.
    In general one might raise the question, to what kind of science
it belongs to discuss the difficulties about the matter of the
objects of mathematics. Neither to physics (because the whole
inquiry of the physicist is about the things that have in
themselves a principle. of movement and rest), nor yet to the
science which inquires into demonstration and science; for this is
just the subject which it investigates. It remains then that it is
the philosophy which we have set before ourselves that treats of
those subjects.
    One might discuss the question whether the science we are
seeking should be said to deal with the principles which are by
some called elements; all men suppose these to be present in
composite things. But it might be thought that the science we seek
should treat rather of universals; for every definition and every
science is of