taph._ viii (Did. vii,
6), against Plato, that if the idea of an animal is distinct from the
idea of a biped, then a biped animal is not absolutely one. For this
reason, against those who hold that there are several souls in the
body, he asks (De Anima i, 5), "what contains them?"--that is, what
makes them one? It cannot be said that they are united by the one
body; because rather does the soul contain the body and make it one,
than the reverse.

Secondly, this is proved to be impossible by the manner in which one
thing is predicated of another. Those things which are derived from
various forms are predicated of one another, either accidentally, (if
the forms are not ordered to one another, as when we say that
something white is sweet), or essentially, in the second manner of
essential predication, (if the forms are ordered one to another, the
subject belonging to the definition of the predicate; as a surface is
presupposed to color; so that if we say that a body with a surface is
colored, we have the second manner of essential predication.)
Therefore, if we have one form by which a thing is an animal, and
another form by which it is a man, it follows either that one of these
two things could not be predicated of the other, except accidentally,
supposing these two forms not to be ordered to one another--or that
one would be predicated of the other according to the second manner of
essential predication, if one soul be presupposed to the other. But
both of these consequences are clearly false: because "animal" is
predicated of man essentially and not accidentally; and man is not
part of the definition of an animal, but the other way about.
Therefore of necessity by the same form a thing is animal and man;
otherwise man would not really be the thing which is an animal, so
that animal can be essentially predicated of man.

Thirdly, this is shown to be impossible by the fact that when one
operation of the soul is intense it impedes another, which could never
be the case unless the principle of action were essentially one.

We must therefore conclude that in man the sensitive soul, the
intellectual soul, and the nutritive soul are numerically one soul.
This can easily be explained, if we consider the differences of
species and forms. For we observe that the species and forms of things
differ from one another, as the perfect and imperfect; as in the order
of things, the animate are more perfect than the inanimate, and
ani