Whether incest is a determinate species of lust?

❌ Objection 1 : It would seem that incest is not a determinate species of lust. For incest [*'Incestus' is equivalent to 'in-castus = 'unchaste'] takes its name from being a privation of chastity. But all kinds of lust are opposed to chastity. Therefore it seems that incest is not a species of lust, but is lust itself in general.

❌ Objection 2 : Further, it is stated in the Decretals (XXXVI, qu. 1 [*Cf. Append. Grat. ad can. Lex illa]) that "incest is intercourse between a man and a woman related by consanguinity or affinity." Now affinity differs from consanguinity. Therefore it is not one but several species of lust.

❌ Objection 3 : Further, that which does not, of itself, imply a deformity, does not constitute a determinate species of vice. But intercourse between those who are related by consanguinity or affinity does not, of itself, contain any deformity, else it would never have been lawful. Therefore incest is not a determinate species of lust.