n
is sinful, because virtue is corrupted by "excess" and "deficiency"
as stated in _Ethic._ ii, 2. Now in every venereal act there is
excess of pleasure, since it so absorbs the mind, that "it is
incompatible with the act of understanding," as the Philosopher
observes (Ethic. vii, 11); and as Jerome [*Origen, Hom. vi in Num.;
Cf. Jerome, Ep. cxxiii ad Ageruch.] states, rendered the hearts of
the prophets, for the moment, insensible to the spirit of prophecy.
Therefore no venereal act can be without sin.

Obj. 3: Further, the cause is more powerful than its effect. Now
original sin is transmitted to children by concupiscence, without
which no venereal act is possible, as Augustine declares (De Nup. et
Concup. i, 24). Therefore no venereal act can be without sin.

_On the contrary,_ Augustine says (De Bono Conjug. xxv): "This is a
sufficient answer to heretics, if only they will understand that no
sin is committed in that which is against neither nature, nor morals,
nor a commandment": and he refers to the act of sexual intercourse
between the patriarchs of old and their several wives. Therefore not
every venereal act is a sin.

_I answer that,_ A sin, in human acts, is that which is against the
order of reason. Now the order of reason consists in its ordering
everything to its end in a fitting manner. Wherefore it is no sin if
one, by the dictate of reason, makes use of certain things in a
fitting manner and order for the end to which they are adapted,
provided this end be something truly good. Now just as the
preservation of the bodily nature of one individual is a true good,
so, too, is the preservation of the nature of the human species a
very great good. And just as the use of food is directed to the
preservation of life in the individual, so is the use of venereal
acts directed to the preservation of the whole human race. Hence
Augustine says (De Bono Conjug. xvi): "What food is to a man's well
being, such is sexual intercourse to the welfare of the whole human
race." Wherefore just as the use of food can be without sin, if it be
taken in due manner and order, as required for the welfare of the
body, so also the use of venereal acts can be without sin, provided
they be performed in due manner and order, in keeping with the end of
human procreation.

Reply Obj. 1: A thing may be a hindrance to virtue in two ways.
First, as regards the ordinary degree of virtue, and as to this
nothing but sin is an obstacle to v