ution, without any
copulation, for the sake of venereal pleasure: this pertains to the
sin of "uncleanness" which some call "effeminacy." Secondly, by
copulation with a thing of undue species, and this is called
"bestiality." Thirdly, by copulation with an undue sex, male with
male, or female with female, as the Apostle states (Rom. 1:27): and
this is called the "vice of sodomy." Fourthly, by not observing the
natural manner of copulation, either as to undue means, or as to
other monstrous and bestial manners of copulation.

Reply Obj. 1: There we enumerated the species of lust that are not
contrary to human nature: wherefore the unnatural vice was omitted.

Reply Obj. 2: Bestiality differs from vice, for the latter is opposed
to human virtue by a certain excess in the same matter as the virtue,
and therefore is reducible to the same genus.

Reply Obj. 3: The lustful man intends not human generation but
venereal pleasures. It is possible to have this without those acts
from which human generation follows: and it is that which is sought
in the unnatural vice.
_______________________

TWELFTH ARTICLE [II-II, Q. 154, Art. 12]

Whether the Unnatural Vice Is the Greatest Sin Among the Species of
Lust?

Objection 1: It would seem that the unnatural vice is not the
greatest sin among the species of lust. For the more a sin is
contrary to charity the graver it is. Now adultery, seduction and
rape which are injurious to our neighbor are seemingly more contrary
to the love of our neighbor, than unnatural sins, by which no other
person is injured. Therefore the unnatural sin is not the greatest
among the species of lust.

Obj. 2: Further, sins committed against God would seem to be the most
grievous. Now sacrilege is committed directly against God, since it
is injurious to the Divine worship. Therefore sacrilege is a graver
sin than the unnatural vice.

Obj. 3: Further, seemingly, a sin is all the more grievous according
as we owe a greater love to the person against whom that sin is
committed. Now the order of charity requires that a man love more
those persons who are united to him--and such are those whom he
defiles by incest--than persons who are not connected with him, and
whom in certain cases he defiles by the unnatural vice. Therefore
incest is a graver sin than the unnatural vice.

Obj. 4: Further, if the unnatural vice is most grievous, the more it
is against nature the graver it would seem to be. Now the si