life, against an unjust aggressor, who we suppose does you an injury,
and thereby gives you no choice but to call him out, or calls you out,
and accordingly assails you in words, &c. Hence, as for the needful
defence of reputation, or of goods of fortune of great consequence, it
is lawful, with the moderation of a blameless defence, to kill an
unjust aggressor, so it will be also lawful to offer and accept a
duel, and therein slay the other party." Reiffenstuel here evidently
supposes that killing done in self-defence is _direct_. Those who
agree with him on that point, proceed to draw differences between
self-defence and accepting a challenge. Of course the two are not the
same. The true difficulty for them lies in making out how the reasons
which justify self-defence in their view of it, do not also justify
the acceptance of a duel: how, if I may make another man's death a
means to the preservation of my vital right, I may not as well make
another man's risk of death and my own, which is all that a duel
amounts to, also a _means_, none other being at hand, to the
preserving of my no less vital right. This grave objection does not
touch us. We have denied that killing in self-defence is direct. On
the lines of that denial we meet Reiffenstuel's argument simply as
follows.

3. In self-defence, the aggressor is slain _indirectly_. In a duel,
not indeed the death itself, or mutual slaughter of the combatants, is
_directly_ willed, but the risk of mutual slaughter is directly
willed. But we may not directly will the risk of that which we may not
directly do. And the combatants may not directly do themselves or one
another to death. Therefore they may not directly risk each his own
and his antagonist's life. But this risk is of the essence of a duel.
Therefore duelling is essentially unlawful.