Summa Theologica

We must next consider the vice of lust which is opposed to chastity: (1) Lust in general; (2) its species. Under the first head there are five points of inquiry:

(1) What is the matter of lust?

(2) Whether all copulation is unlawful?

(3) Whether lust is a mortal sin?

(4) Whether lust is a capital vice?

(5) Concerning its daughters.