the act of the
reason is, as it were, a movement from one thing to another. But the
same movable thing passes through the medium and reaches the end.
Wherefore the higher and lower reasons are one and the same power.
But according to Augustine they are distinguished by the functions of
their actions, and according to their various habits: for wisdom is
attributed to the higher reason, science to the lower.

Reply Obj. 1: We speak of parts, in whatever way a thing is divided.
And so far as reason is divided according to its various acts, the
higher and lower reason are called parts; but not because they are
different powers.

Reply Obj. 2: The lower reason is said to flow from the higher, or
to be ruled by it, as far as the principles made use of by the lower
reason are drawn from and directed by the principles of the higher
reason.

Reply Obj. 3: The "scientific" part, of which the Philosopher speaks,
is not the same as the higher reason: for necessary truths are found
even among temporal things, of which natural science and mathematics
treat. And the "opinionative" and "ratiocinative" part is more
limited than the lower reason; for it regards only things contingent.
Neither must we say, without any qualification, that a power, by
which the intellect knows necessary things, is distinct from a power
by which it knows contingent things: because it knows both under the
same objective aspect--namely, under the aspect of being and truth.
Wherefore it perfectly knows necessary things which have perfect
being in truth; since it penetrates to their very essence, from which
it demonstrates their proper accidents. On the other hand, it knows
contingent things, but imperfectly; forasmuch as they have but
imperfect being and truth. Now perfect and imperfect in the action do
not vary the power, but they vary the actions as to the mode of
acting, and consequently the principles of the actions and the habits
themselves. And therefore the Philosopher postulates two lesser parts
of the soul--namely, the "scientific" and the "ratiocinative," not
because they are two powers, but because they are distinct according
to a different aptitude for receiving various habits, concerning the
variety of which he inquires. For contingent and necessary, though
differing according to their proper genera, nevertheless agree in the
common aspect of being, which the intellect considers, and to which
they are variously compared as perfect and imperfect