he powers vary, but only what
cannot be reduced to the one same principle, as we have said above
(Q. 78, A. 4).
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ELEVENTH ARTICLE [I, Q. 79, Art. 11]

Whether the Speculative and Practical Intellects Are Distinct Powers?

Objection 1: It would seem that the speculative and practical
intellects are distinct powers. For the apprehensive and motive are
different kinds of powers, as is clear from _De Anima_ ii, 3. But
the speculative intellect is merely an apprehensive power; while the
practical intellect is a motive power. Therefore they are distinct
powers.

Obj. 2: Further, the different nature of the object differentiates
the power. But the object of the speculative intellect is _truth,_
and of the practical is _good;_ which differ in nature. Therefore the
speculative and practical intellect are distinct powers.

Obj. 3: Further, in the intellectual part, the practical intellect is
compared to the speculative, as the estimative is to the imaginative
power in the sensitive part. But the estimative differs from the
imaginative, as power form power, as we have said above (Q. 78, A.
4). Therefore also the speculative intellect differs from the
practical.

_On the contrary,_ The speculative intellect by extension becomes
practical (De Anima iii, 10). But one power is not changed into
another. Therefore the speculative and practical intellects are not
distinct powers.

_I answer that,_ The speculative and practical intellects are not
distinct powers. The reason of which is that, as we have said above
(Q. 77, A. 3), what is accidental to the nature of the object of
a power, does not differentiate that power; for it is accidental to a
thing colored to be man, or to be great or small; hence all such
things are apprehended by the same power of sight. Now, to a thing
apprehended by the intellect, it is accidental whether it be directed
to operation or not, and according to this the speculative and
practical intellects differ. For it is the speculative intellect which
directs what it apprehends, not to operation, but to the consideration
of truth; while the practical intellect is that which directs what it
apprehends to operation. And this is what the Philosopher says (De
Anima iii, 10); that "the speculative differs from the practical in
its end." Whence each is named from its end: the one speculative, the
other practical--i.e. operative.

Reply Obj. 1: The practical intellect is a motive power,