circumstance, as
such, is an accident of the moral act: and yet a circumstance may
happen to be taken as the specific difference of a moral act, and
then it loses its nature of circumstance, and constitutes the species
of the moral act. This happens in sins when a circumstance adds the
deformity of another genus; thus when a man has knowledge of another
woman than his wife, the deformity of his act is opposed to chastity;
but if this other be another man's wife, there is an additional
deformity opposed to justice which forbids one to take what belongs
to another; and accordingly this circumstance constitutes a new
species of sin known as adultery.

It is, however, impossible for a circumstance to make a venial sin
become mortal, unless it adds the deformity of another species. For
it has been stated above (A. 1) that the deformity of a venial sin
consists in a disorder affecting things that are referred to the end,
whereas the deformity of a mortal sin consists in a disorder about
the last end. Consequently it is evident that a circumstance cannot
make a venial sin to be mortal, so long as it remains a circumstance,
but only when it transfers the sin to another species, and becomes,
as it were, the specific difference of the moral act.

Reply Obj. 1: Length of time is not a circumstance that draws a sin
to another species, nor is frequency or custom, except perhaps by
something accidental supervening. For an action does not acquire a
new species through being repeated or prolonged, unless by chance
something supervene in the repeated or prolonged act to change its
species, e.g. disobedience, contempt, or the like.

We must therefore reply to the objection by saying that since anger
is a movement of the soul tending to the hurt of one's neighbor, if
the angry movement tend to a hurt which is a mortal sin generically,
such as murder or robbery, that anger will be a mortal sin
generically: and if it be a venial sin, this will be due to the
imperfection of the act, in so far as it is a sudden movement of the
sensuality: whereas, if it last a long time, it returns to its
generic nature, through the consent of reason. If, on the other hand,
the hurt to which the angry movement tends, is a sin generically
venial, for instance, if a man be angry with someone, so as to wish
to say some trifling word in jest that would hurt him a little, the
anger will not be mortal sin, however long it last, unless perhaps
accidentally; for