ccording to what is
intended, and not according to what is beside the intention, since
this is accidental as explained above (Q. 43, A. 3; I-II, Q. 12, A.
1). Accordingly the act of self-defense may have two effects, one is
the saving of one's life, the other is the slaying of the aggressor.
Therefore this act, since one's intention is to save one's own life,
is not unlawful, seeing that it is natural to everything to keep
itself in _being,_ as far as possible. And yet, though proceeding
from a good intention, an act may be rendered unlawful, if it be out
of proportion to the end. Wherefore if a man, in self-defense, uses
more than necessary violence, it will be unlawful: whereas if he
repel force with moderation his defense will be lawful, because
according to the jurists [*Cap. Significasti, De Homicid. volunt. vel
casual.], "it is lawful to repel force by force, provided one does
not exceed the limits of a blameless defense." Nor is it necessary
for salvation that a man omit the act of moderate self-defense in
order to avoid killing the other man, since one is bound to take more
care of one's own life than of another's. But as it is unlawful to
take a man's life, except for the public authority acting for the
common good, as stated above (A. 3), it is not lawful for a man to
intend killing a man in self-defense, except for such as have public
authority, who while intending to kill a man in self-defense, refer
this to the public good, as in the case of a soldier fighting against
the foe, and in the minister of the judge struggling with robbers,
although even these sin if they be moved by private animosity.

Reply Obj. 1: The words quoted from Augustine refer to the case when
one man intends to kill another to save himself from death. The
passage quoted in the Second Objection is to be understood in the
same sense. Hence he says pointedly, "for the sake of these things,"
whereby he indicates the intention. This suffices for the Reply to
the Second Objection.

Reply Obj. 3: Irregularity results from the act though sinless of
taking a man's life, as appears in the case of a judge who justly
condemns a man to death. For this reason a cleric, though he kill a
man in self-defense, is irregular, albeit he intends not to kill him,
but to defend himself.

Reply Obj. 4: The act of fornication or adultery is not necessarily
directed to the preservation of one's own life, as is the act whence
sometimes results the taking of a