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.
Obj. 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.
Obj. 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.
_On the contrary,_ The species of lust are distinguished according to
the various conditions of women with whom a man has unlawful
intercourse. Now incest implies a special condition on the part of
the woman, because it is unlawful intercourse with a woman related by
consanguinity or affinity as stated (Obj. 2). Therefore incest is a
determinate species of lust.
_I answer that,_ As stated above (AA. 1, 6) wherever we find
something incompatible with the right use of venereal actions, there
must needs be a determinate species of lust. Now sexual intercourse
with women related by consanguinity or affinity is unbecoming to
venereal union on three counts. First, because man naturally owes a
certain respect to his parents and therefore to his other blood
relations, who are descended in near degree from the same parents: so
much so indeed that among the ancients, as Valerius Maximus relates
[*Dict. Fact. Memor. ii, 1], it was not deemed right for a son to
bathe with his father, lest they should see one another naked. Now
from what has been said (Q. 142, A. 4; Q. 151, A. 4), it is evident
that in venereal acts there is a certain shamefulness inconsistent
with respect, wherefore men are ashamed of them. Wherefore it is
unseemly that such persons should be united in venereal intercourse.
This reason seems to be indicated (Lev. 18:7) where we read: "She is
thy mother, thou shalt not uncover her nakedness," and the same is
expressed further on with regard to others.
The second reason is because blood relations must needs live in close
touch with one another. Wherefore if they were not debarred from
venereal union, opportunities of venereal intercourse would be very
frequent and thus men's minds would be enervated by lust. Hence in
the Old Law [*Lev. 18] the prohibition was apparently directed
specially to those persons who must needs live together.
The third reason is, because this would hinder a man from having many
friends: since through a man taking a stranger to wife, all his
wife's relations are united to him by a special kind of friendship,
as though they were of the same blood as himself. Wherefore Augustine
says (De Civ. Dei xv, 16): "The demands of charity are most perfectly
satisfied by men uniting together in the bonds that the various ties
of friendship require, so that they may live together in a useful and
becoming amity; nor should one man have many relationships in one,
but each should have one."
Aristotle adds another reason (2 Polit. ii): for since it is natural
that a man should have a liking for a woman of his kindred, if to
this be added the love that has its origin in venereal intercourse,
his love would be too ardent and would become a very great incentive
to lust: and this is contrary to chastity. Hence it is evident that
incest is a determinate species of lust.
Reply Obj. 1: Unlawful intercourse between persons related to one
another would be most prejudicial to chastity, both on account of the
opportunities it affords, and because of the excessive ardor of love,
as stated in the Article. Wherefore the unlawful intercourse between
such persons is called "incest" antonomastically.
Reply Obj. 2: Persons are related by affinity through one who is
related by consanguinity: and therefore since the one depends on the
other, consanguinity and affinity entail the same kind of
unbecomingness.
Reply Obj. 3: There is something essentially unbecoming and contrary
to natural reason in sexual intercourse between persons related by
blood, for instance between parents and children who are directly and
immediately related to one another, since children naturally owe
their parents honor. Hence the Philosopher instances a horse (De
Animal. ix, 47) which covered its own mother by mistake and threw
itself over a precipice as though horrified at what it had done,
because some animals even have a natural respect for those that have
begotten them. There is not the same essential unbecomingness
attaching to other persons who are related to one another not
directly but through their parents: and, as to this, becomingness or
unbecomingness varies according to custom, and human or Divine law:
because, as stated above (A. 2), sexual intercourse, being directed
to the common good, is subject to law. Wherefore, as Augustine says
(De Civ. Dei xv, 16), whereas the union of brothers and sisters goes
back to olden times, it became all the more worthy of condemnation
when religion forbade it.
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