For it is not every kind of Notion which the pleasant and the painful corrupt and pervert, as, for instance, that “the three angles of every rectilineal triangle are equal to two right angles,” but only those bearing on moral action.
For the Principles of the matters of moral action are the final cause of them:[1] now to the man who has been corrupted by reason of pleasure or pain the Principle immediately becomes obscured, nor does he see that it is his duty to choose and act in each instance with a view to this final cause and by reason of it: for viciousness has a tendency to destroy the moral Principle: and so Practical Wisdom must be “a state conjoined with reason, true, having human good for its object, and apt to do.”
Then again Art admits of degrees of excellence, but Practical Wisdom does not:[2] and in Art he who goes wrong purposely is preferable to him who does so unwittingly, but not so in respect of Practical Wisdom or the other Virtues.[3] It plainly is then an Excellence of a certain kind, and not an Art.
Now as there are two parts of the Soul which have Reason, it must be the Excellence of the Opinionative [which we called before calculative or deliberative], because both Opinion and Practical Wisdom are exercised upon Contingent matter. And further, it is not simply a state conjoined with Reason, as is proved by the fact that such a state may be forgotten and so lost while Practical Wisdom cannot.
