In my first post I noted that Thomas Aquinas utilized St. Augustine's definition of virtue. Augustine stated that virtue was a habit "by which we live righteously, of which no one can make bad use, which God works in us, without us" (Augustine, On Free Will). For Aquinas this is a good working definition. But in order to understand his distinction between intellectual and moral virtue, we need to hear Aquinas' own understanding:
"Virtue denotes a certain perfection of a power. Now a thing's perfection is considered chiefly in regard to its end. But the end of power is act. Wherefore power is said to be perfect, according as it is determinate to its act. Now there are some powers which of themselves are determinate to their acts; for instance, the active natural powers. These natural powers are in themselves called virtues. but the rational powers, which are proper to humanity, are not determinate to one particular action, but are inclined indifferently to many: and they are determinate to acts by means of habits, as is clear from what we have said above. therefore human virtues are habits" (Summa Theologica, II).
What does it mean that virtue is a certain perfection of a power. For Thomas, powers fall under two categories: natural and rational. Natural powers refer to the attributes of God. Such powers are natural and therefore perfect because they are untainted by the fall. Thus for Aquinas the word "natural" cannot be used for creation post-Eden since it is tainted by sin and therefore in an unnatural state. Natural powers must relate only to God.
Rational powers refer to those attributes that are as Aquinas states, "proper to humanity." Intellectual virtues are those habits that move men and women toward the perfection of the intellect, theoretical and practical. For Thomas, three virtues that perfect the intellect are understanding, science and wisdom. Understanding comprehends first principles, science apprehends truth, and wisdom recognizes higher causes, preeminently God.
Again these three are virtues in that they employ the rational that seeks the natural, thus they are proper. But Thomas knows that this raises the inevitable question that he himself premptively asks in the Summa: "Can there be intellectual virtue without moral virtue?" If Augustine is correct that virtue is a habit "of which no one can make bad use," how does Aquinas explain the destructive use often made of the intellectual "virtues" of understanding, science, and wisdom?