Now, just as, in the speculative reason, there are certain things naturally known, about which is understanding, and certain things of which we obtain knowledge through them, viz. conclusions, about which is science, so in the practical reason, certain things pre-exist, as naturally known principles, and such are the ends of the moral virtues, since the end is in practical matters what principles are in speculative matters, as stated above (Q. 23, A. 7, ad 2; I-II, Q. 13, A. 3); while certain things are in the practical reason by way of conclusions, and such are the means which we gather from the ends themselves. About these is prudence, which applies universal principles to the particular conclusions of practical matters. Consequently it does not belong to prudence to appoint the end to moral virtues, but only to regulate the means.
Reply Obj. 1: Natural reason known by the name of synderesis appoints the end to moral virtues, as stated above (I, Q. 79, A. 12): but prudence does not do this for the reason given above.
This suffices for the Reply to the Second Objection.
Reply Obj. 3: The end concerns the moral virtues, not as though they appointed the end, but because they tend to the end which is appointed by natural reason. In this they are helped by prudence, which prepares the way for them, by disposing the means. Hence it follows that prudence is more excellent than the moral virtues, and moves them: yet synderesis moves prudence, just as the understanding of principles moves science. _______________________
SEVENTH ARTICLE [II-II, Q. 47, Art. 7]
Whether It Belongs to Prudence to Find the Mean in Moral Virtues?
Objection 1: It would seem that it does not belong to prudence to find the mean in moral virtues. For the achievement of the mean is the end of moral virtues. But prudence does not appoint the end to moral virtues, as shown above (A. 6). Therefore it does not find the mean in them.
Obj. 2: Further, that which of itself has being, would seem to have no cause, but its very being is its cause, since a thing is said to have being by reason of its cause. Now "to follow the mean" belongs to moral virtue by reason of itself, as part of its definition, as shown above (A. 5, Obj. 1). Therefore prudence does not cause the mean in moral virtues.
Obj. 3: Further, prudence works after the manner of reason. But moral virtue tends to the mean after the manner of nature, because, as Tully states (De Invent. Rhet. ii, 53), "virtue is a habit like a second nature in accord with reason." Therefore prudence does not appoint the mean to moral virtues.
On the contrary, In the foregoing definition of moral virtue (A. 5, Obj. 1) it is stated that it "follows a mean appointed by reason . . . even as a wise man decides."