79, Art. 8]

Whether the Reason Is Distinct from the Intellect?

Objection 1: It would seem that the reason is a distinct power from
the intellect. For it is stated in _De Spiritu et Anima_ that "when we
wish to rise from lower things to higher, first the sense comes to our
aid, then imagination, then reason, then the intellect." Therefore the
reason is distinct from the intellect, as imagination is from sense.

Obj. 2: Further, Boethius says (De Consol. iv, 6), that intellect is
compared to reason, as eternity to time. But it does not belong to
the same power to be in eternity and to be in time. Therefore reason
and intellect are not the same power.

Obj. 3: Further, man has intellect in common with the angels, and
sense in common with the brutes. But reason, which is proper to man,
whence he is called a rational animal, is a power distinct from sense.
Therefore is it equally true to say that it is distinct from the
intellect, which properly belongs to the angel: whence they are called
intellectual.

_On the contrary,_ Augustine says (Gen. ad lit. iii, 20) that "that
in which man excels irrational animals is reason, or mind, or
intelligence or whatever appropriate name we like to give it."
Therefore, reason, intellect and mind are one power.

_I answer that,_ Reason and intellect in man cannot be distinct
powers. We shall understand this clearly if we consider their
respective actions. For to understand is simply to apprehend
intelligible truth: and to reason is to advance from one thing
understood to another, so as to know an intelligible truth. And
therefore angels, who according to their nature, possess perfect
knowledge of intelligible truth, have no need to advance from one
thing to another; but apprehend the truth simply and without mental
discussion, as Dionysius says (Div. Nom. vii). But man arrives at
the knowledge of intelligible truth by advancing from one thing to
another; and therefore he is called rational. Reasoning, therefore,
is compared to understanding, as movement is to rest, or acquisition
to possession; of which one belongs to the perfect, the other to the
imperfect. And since movement always proceeds from something
immovable, and ends in something at rest; hence it is that human
reasoning, by way of inquiry and discovery, advances from certain
things simply understood--namely, the first principles; and, again,
by way of judgment returns by analysis to first principles, in the
light of whi