There are two reasons for studying intellectual virtue:
- Because the virtuous man has been defined as one who acts in accordance with a right rule and this right rule is arrived at by intellectual processes.
- Because true happiness has been defined as an activity of the soul in conformity with virtue, and virtue (excellence) exists in the intellectual as well as the moral sphere.
As shown in Book I, the soul has two parts — the rational and the irrational. The rational faculty, which processes information and formulates rules, is itself divided into two parts. These are:
- The scientific faculty, by which man is enabled to comprehend non-contingent objects (i.e., things whose fundamental or first principles are not subject to variation).
- The calculative faculty, by which man is enabled to deliberate (i.e., to study things which are capable of variation and change, also known as contingent things).