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

A: 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.

On the other hand, a truth which is known through another, is understood by the intellect, not at once, but by means of the reason's inquiry, and is as a
term.
This may happen in two ways: first, so that it is the last in some particular genus; secondly, so that it is the ultimate term of all human knowledge. And, since "things that are knowable last from our standpoint, are knowable first and chiefly in their nature" (Phys. i, text. 2, 3); hence that which is last with respect to all human knowledge, is that which is knowable first and chiefly in its nature. And about these is
wisdom,
which considers the highest causes, as stated in Metaph. i, 1, 2. Wherefore it rightly judges all things and sets them in order, because there can be no perfect and universal judgment that is not based on the first causes. But in regard to that which is last in this or that genus of knowable matter, it is
science
which perfects the intellect. Wherefore according to the different kinds of knowable matter, there are different habits of scientific knowledge; whereas there is but one wisdom.

Reply Obj. 1: Wisdom is a kind of science, in so far as it has that which is common to all the sciences; viz. to demonstrate conclusions from principles. But since it has something proper to itself above the other sciences, inasmuch as it judges of them all, not only as to their conclusions, but also as to their first principles, therefore it is a more perfect virtue than science.

Reply Obj. 2: When the formal aspect of the object is referred to a power or habit by one same act, there is no distinction of habit or power in respect of the formal aspect and of the material object: thus it belongs to the same power of sight to see both color, and light, which is the formal aspect under which color is seen, and is seen at the same time as the color. On the other hand, the principles of a demonstration can be considered apart, without the conclusion being considered at all. Again they can be considered together with the conclusions, since the conclusions can be deduced from them. Accordingly, to consider the principles in this second way, belongs to science, which considers the conclusions also: while to consider the principles in themselves belongs to understanding.

Consequently, if we consider the point aright, these three virtues are distinct, not as being on a par with one another, but in a certain order. The same is to be observed in potential wholes, wherein one part is more perfect than another; for instance, the rational soul is more perfect than the sensitive soul; and the sensitive, than the vegetal. For it is thus that science depends on understanding as on a virtue of higher degree: and both of these depend on wisdom, as obtaining the highest place, and containing beneath itself both understanding and science, by judging both of the conclusions of science, and of the principles on which they are based.

Reply Obj. 3: As stated above (Q. 55, AA. 3, 4), a virtuous habit has a fixed relation to good, and is nowise referable to evil. Now the good of the intellect is truth, and falsehood is its evil. Wherefore those habits alone are called intellectual virtues, whereby we tell the truth and never tell a falsehood. But opinion and suspicion can be about both truth and falsehood: and so, as stated in
Ethic.
vi, 3, they are not intellectual virtues.