Article IV. On Impure Speech and Readings

I say. To speak, hear, or read base things for the sake of venereal pleasure or with proximate danger of consent to it is a grave sin, as is evident of itself. But if the danger is not proximate, or indeed is proximate but at the same time there is a just cause of speaking, hearing, or reading those base things, the sin will be either none or only venial. But what is said here about the base is not to be applied to speech simply obscene.

You Will Resolve. - 1st. Generally they sin gravely who mingle conversations, even from levity, concerning the conjugal act, concerning licit and illicit things between spouses, concerning modes of impeding generation, of procuring pollution ... especially if this happens among young persons of diverse sex. Likewise those who from boasting narrate their own base sins.

2nd. It is not of itself mortal to utter things that are indeed base but not gravely such, if this is done briefly, through jest or vain solace, unless the hearers are so weak in spirit that they suffer grave scandal. - Cf. St. Alphonsus, n. 426.

3rd. Tender conversations with persons of diverse sex are not always to be held as mortal, although they are full of dangers, especially if they are long-lasting, often repeated, or happen in solitary places. - Cf. St. Alphonsus, nn. 422 and following.

4th. They do not sin gravely who from mere curiosity read entertaining books, because they do not excite gravely to lust, nor expose to great danger, as many comedies or poems are. But if they do this for a legitimate cause, e.g., to learn style, they do not sin at all.