Chapter III. On Unnatural Consummated Lust

I. Unnatural consummated lust is: a completed venereal act which is unsuited for generation. Moreover, in order that an act be of itself apt for generation, there are required: 1. the carnal union of two; 2. the union of two of the same species; 3. the union of two of diverse sex; 4. union in the due vessel of the diverse sex. Hence there are four species of lust against nature, namely: pollution, which excludes the union of two; bestiality, which excludes the union of two of the same species; sodomy, which excludes the union of two of diverse sex; finally, intercourse which excludes union in the due vessel of the diverse sex (St. Thomas, II-II, q. 154, a. 11; St. Alphonsus III, 412).

II. The enumerated sins differ in species, because in morally diverse ways they are repugnant to right seminal emission (St. Alphonsus III, 464). There is added proposition 24 condemned by Alexander VII: Softness, sodomy, and bestiality are sins of the same lowest species, and therefore it is enough to say in confession that one has procured pollution.

III. Concerning the relative gravity of the said sins, take these words of St. Thomas: "Gravity in sin is considered more from the abuse of some thing than from the omission of due use; and therefore among the vices which are against nature, the sin of uncleanness holds the lowest place, which consists in the mere omission of intercourse with another (pollution); but the gravest is the sin of bestiality, because the due species is not preserved; hence on that verse of Genesis 37, 'He accused his brothers of a most wicked crime,' the Gloss says that they were mingled with beasts. After this is the vice of sodomy, since there the due sex is not preserved; after this is the sin from the fact that the due manner of lying together is not preserved; but more if there is not the due vessel, than if there is disorder according to some other things pertaining to the manner of intercourse" (II-II, q. 154, a. 12, ad 4).

With these things having been noted generally, we shall speak specifically about the individual unnatural sins.