power, as the action
of the imagination by the action of the senses. Therefore one power
of the soul is caused by another.

_I answer that,_ In those things which proceed from one according to
a natural order, as the first is the cause of all, so that which is
nearer to the first is, in a way, the cause of those which are more
remote. Now it has been shown above (A. 4) that among the powers of
the soul there are several kinds of order. Therefore one power of the
soul proceeds from the essence of the soul by the medium of another.
But since the essence of the soul is compared to the powers both as a
principle active and final, and as a receptive principle, either
separately by itself, or together with the body; and since the agent
and the end are more perfect, while the receptive principle, as such,
is less perfect; it follows that those powers of the soul which
precede the others, in the order of perfection and nature, are the
principles of the others, after the manner of the end and active
principle. For we see that the senses are for the sake of the
intelligence, and not the other way about. The senses, moreover, are
a certain imperfect participation of the intelligence; wherefore,
according to their natural origin, they proceed from the intelligence
as the imperfect from the perfect. But considered as receptive
principles, the more perfect powers are principles with regard to the
others; thus the soul, according as it has the sensitive power, is
considered as the subject, and as something material with regard to
the intelligence. On this account, the more imperfect powers precede
the others in the order of generation, for the animal is generated
before the man.

Reply Obj. 1: As the power of the soul flows from the essence, not
by a transmutation, but by a certain natural resultance, and is
simultaneous with the soul, so is it the case with one power as
regards another.

Reply Obj. 2: An accident cannot of itself be the subject of an
accident; but one accident is received prior to another into
substance, as quantity prior to quality. In this sense one accident
is said to be the subject of another; as surface is of color,
inasmuch as substance receives an accident through the means of
another. The same thing may be said of the powers of the soul.

Reply Obj. 3: The powers of the soul are opposed to one another, as
perfect and imperfect; as also are the species of numbers and
figures. But this opposition does no