The horrendous crime of sodomy is sexual intercourse with a person of the same or different sex, but in an undue vessel. Hence a twofold kind is distinguished: 1st. perfect, which is sexual intercourse with a person of the same sex; 2nd. imperfect, which is sexual intercourse with a person of different sex outside the natural vessel.
I say 1st. Sodomy is a crime much graver than simple pollution. This is clear from the horror which it excites among all, and also from the unheard-of punishments inflicted by God upon Sodom and the other cities defiled by this sin.
I say 2nd. Perfect sodomy differs in species from imperfect, because to be carried toward the sex and toward the undue vessel contains a double special malice. But although imperfect sodomy is itself also a great sin, nevertheless when sodomy is named without qualification, only perfect sodomy is understood, especially where it concerns censures and reservation, unless the superior has declared the contrary. - Cf. St. Alphonsus, n. 471.
You Will Ask. Must it be declared in confession who was agent or patient in sodomy?
Response. Negatively, because the species of the sin is the same: but the circumstance of pollution, which can happen more easily in the agent, is altogether to be declared. - Cf. St. Alphonsus, n. 468.