448. (iv) Fornication is a lust, but not a lust for adultery.

The reasons why fornication is lust are: (a) it arises from the natural man, and everything which arises from that is desire and lust. For the natural man is nothing but a container and home for desires and lusts, since all kinds of guilt inherited from parents live there. (b) A fornicator casts a roving and promiscuous eye on the other sex, not yet limiting himself to one of that sex. So long as he is in that state, lust drives him to do what he does. But when he looks to only one woman, and loves to join his life with hers, desire turns into a chaste affection and lust into a civilised love.