Objection 1:  It would seem that vice is not contrary to virtue.  For one thing has one contrary, as proved in Metaph. x, text. 17.  Now sin and malice are contrary to virtue.  Therefore vice is not contrary to it:  since vice applies also to undue disposition of bodily members or of any things whatever.

Obj. 2:  Further, virtue denotes a certain perfection of power.  But vice does not denote anything relative to power.  Therefore vice is not contrary to virtue.

Obj. 3:  Further, Cicero (De Quaest.  Tusc. iv) says that “virtue is the soul’s health.”  Now sickness or disease, rather than vice, is opposed to health.  Therefore vice is not contrary to virtue.

On the contrary, Augustine says (De Perfect.  Justit. ii) that “vice is a quality in respect of which the soul is evil.”  But “virtue is a quality which makes its subject good,” as was shown above (Q. 55, AA. 3, 4).  Therefore vice is contrary to virtue.

I answer that, Two things may be considered in virtue—­the essence of virtue, and that to which virtue is ordained.  In the essence of virtue we may consider something directly, and we may consider something consequently.  Virtue implies directly a disposition whereby the subject is well disposed according to the mode of its nature:  wherefore the Philosopher says (Phys. vii, text. 17) that “virtue is a disposition of a perfect thing to that which is best; and by perfect I mean that which is disposed according to its nature.”  That which virtue implies consequently is that it is a kind of goodness:  because the goodness of a thing consists in its being well disposed according to the mode of its nature.  That to which virtue is directed is a good act, as was shown above (Q. 56, A. 3).

Accordingly three things are found to be contrary to virtue.  One of these is sin, which is opposed to virtue in respect of that to which virtue is ordained:  since, properly speaking, sin denotes an inordinate act; even as an act of virtue is an ordinate and due act:  in respect of that which virtue implies consequently, viz. that it is a kind of goodness, the contrary of virtue is malice:  while in respect of that which belongs to the essence of virtue directly, its contrary is vice:  because the vice of a thing seems to consist in its not being disposed in a way befitting its nature:  hence Augustine says (De Lib.  Arb. iii):  “Whatever is lacking for a thing’s natural perfection may be called a vice.”

Reply Obj. 1:  These three things are contrary to virtue, but not in the same respect:  for sin is opposed to virtue, according as the latter is productive of a good work; malice, according as virtue is a kind of goodness; while vice is opposed to virtue properly as such.

Reply Obj. 2:  Virtue implies not only perfection of power, the principle of action; but also the due disposition of its subject.  The reason for this is because a thing operates according as it is in act:  so that a thing needs to be well disposed if it has to produce a good work.  It is in this respect that vice is contrary to virtue.