76. No one can know what the chastity of marriage is, unless he shuns the lasciviousness of adultery as sin. A man may know that in which he is, but he cannot know that in which he is not. If from description or thought he knows something in which he is not, still he knows it only as something in the shade, and uncertainty adheres to it. Therefore he does not see it in the light and free from uncertainty, as when he experiences it; and so this is to know, but the other is to know and yet not to know. It is a truth that the lasciviousness of adultery and the chastity of marriage are to each other just as hell and heaven are to each other; and that the lasciviousness of adultery makes hell with man, and the chastity of marriage makes heaven with him. However, the chastity of marriage is only possible with the man who shuns the lasciviousness of adultery as sin. See below, No. 111.