is incorporeal,
and because it is incorruptible. Therefore it seems to be united to
the body by means of an incorruptible body, and such would be some
heavenly light, which would harmonize the elements, and unite them
together.

_On the contrary,_ The Philosopher says (De Anima ii, 1): "We need
not ask if the soul and body are one, as neither do we ask if wax and
its shape are one." But the shape is united to the wax without a body
intervening. Therefore also the soul is thus united to the body.

_I answer that,_ If the soul, according to the Platonists, were united
to the body merely as a motor, it would be right to say that some
other bodies must intervene between the soul and body of man, or any
animal whatever; for a motor naturally moves what is distant from it
by means of something nearer.

If, however, the soul is united to the body as its form, as we have
said (A. 1), it is impossible for it to be united by means of
another body. The reason of this is that a thing is one, according as
it is a being. Now the form, through itself, makes a thing to be
actual since it is itself essentially an act; nor does it give
existence by means of something else. Wherefore the unity of a thing
composed of matter and form, is by virtue of the form itself, which by
reason of its very nature is united to matter as its act. Nor is there
any other cause of union except the agent, which causes matter to be
in act, as the Philosopher says, _Metaph._ viii (Did. vii, 6).

From this it is clear how false are the opinions of those who
maintained the existence of some mediate bodies between the soul and
body of man. Of these certain Platonists said that the intellectual
soul has an incorruptible body naturally united to it, from which it
is never separated, and by means of which it is united to the
corruptible body of man. Others said that the soul is united to the
body by means of a corporeal spirit. Others said it is united to the
body by means of light, which, they say, is a body and of the nature
of the fifth essence; so that the vegetative soul would be united to
the body by means of the light of the sidereal heaven; the sensible
soul, by means of the light of the crystal heaven; and the
intellectual soul by means of the light of the empyrean heaven. Now
all this is fictitious and ridiculous: for light is not a body; and
the fifth essence does not enter materially into the composition of a
mixed body (since it is unchangeable),