76. No one can know the nature of the chastity of marriage except the man who shuns as a sin the lasciviousness of adultery. For a man may know that in which he is, but cannot know that in which he is not. If from description or from thinking about it a man knows something in which he is not, he nevertheless knows of it merely as of something in the dark, and there remains some doubt about it, so that no one sees anything in the light and free from doubt until he is actually in it. This last therefore is to know, whereas the other is both to know and not to know. The truth is that the lasciviousness of adultery and the chastity of marriage stand toward each other exactly as do hell and heaven, and that the lasciviousness of adultery makes hell in a man, and the chastity of marriage makes heaven. But the chastity of marriage exists solely with the man who shuns as sin the lasciviousness of adultery. (See below, n. 111.)