/summa/SS/SSIII/SS_Q151:
We must next consider chastity: (1) The virtue itself of chastity: (2) virginity, which is a part of chastity: (3) lust, which is the contrary vice. Under the first head there are four points of inquiry:
(1) Whether chastity is a virtue?
(2) Whether it is a general virtue?
(3) Whether it is a virtue distinct from abstinence?
(4) Of its relation to purity.