Reply Obj. 2:  Virtue is about certain things in two ways.  In the first place a virtue is about its object.  And thus these speculative virtues are not about those things whereby man is made happy; except perhaps, in so far as the word “whereby” indicates the efficient cause or object of complete happiness, i.e.  God, Who is the supreme object of contemplation.  Secondly, a virtue is said to be about its acts:  and in this sense the intellectual virtues are about those things whereby a man is made happy; both because the acts of these virtues can be meritorious, as stated above, and because they are a kind of beginning of perfect bliss, which consists in the contemplation of truth, as we have already stated (Q. 3, A. 7).

Reply Obj. 3:  Science is contrasted with virtue taken in the second sense, wherein it belongs to the appetitive faculty. ________________________

SECOND ARTICLE [I-II, Q. 57, Art. 2]

Whether There Are Only Three Habits of the Speculative Intellect, Viz. 
Wisdom, Science and Understanding?

Objection 1:  It would seem unfitting to distinguish three virtues of the speculative intellect, viz. wisdom, science and understanding.  Because a species is a kind of science, as stated in Ethic. vi, 7.  Therefore wisdom should not be condivided with science among the intellectual virtues.

Obj. 2:  Further, in differentiating powers, habits and acts in respect of their objects, we consider chiefly the formal aspect of these objects, as we have already explained (I, Q. 77, A. 3).  Therefore diversity of habits is taken, not from their material objects, but from the formal aspect of those objects.  Now the principle of a demonstration is the formal aspect under which the conclusion is known.  Therefore the understanding of principles should not be set down as a habit or virtue distinct from the knowledge of conclusions.

Obj. 3:  Further, an intellectual virtue is one which resides in the essentially rational faculty.  Now even the speculative reason employs the dialectic syllogism for the sake of argument, just as it employs the demonstrative syllogism.  Therefore as science, which is the result of a demonstrative syllogism, is set down as an intellectual virtue, so also should opinion be.

On the contrary, The Philosopher (Ethic. vi, 1) reckons these three alone as being intellectual virtues, viz. wisdom, science and understanding.

I answer that, As already stated (A. 1), the virtues of the speculative intellect are those which perfect the speculative intellect for the consideration of truth:  for this is its good work.  Now a truth is subject to a twofold consideration—­as known in itself, and as known through another.  What is known in itself, is as a principle, and is at once understood by the intellect:  wherefore the habit that perfects the intellect for the consideration of such truth is called understanding, which is the habit of principles.