Case #9: Self-Defense

Thomas Aquinas, Summa Theologica (II-II, Q64, A7) "Whether it is Lawful to Kill a Man in Self-Defense"

Principle of Double Effect

"Nothing hinders one act from having two effects, only one of which is intended, while the other is beside the intention. Now moral acts take their species according to what is intended, and not according to what is beside the intention, since this is accidental and is explained above (II-II Q43, A3; I-II Q. 72, A1). 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, 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 from the common good as stated above (II-II Q. 64, A3), 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 ministry of the judge struggling with robbers, although even these sin if they be moved by private animosity."

Question:

Is it morally permissible for a person to perform an action which brings about, simultaneously, two foreseeable effects, one good and one evil?

Principle of Double Effect (adapted from Odozor, p. 211)

1. The action must be good in itself (or at least neutral)
2. One must intend directly the good rather than the evil effect
3. One must not produce a good effect by means of the evil effect
4. There must be a proportionally grave reason for producing the evil effect

Basic Issues Driving this Debate

1. In the structure of our action, is it possible to neatly separate what we directly intend and what we allow (or indirectly intend)?
2. What exactly do we will when we make a choice? Do we, as John Paul II suggests, elect "a certain kind of behavior"? Or is human action as such best understood as an attempt to maximize non-moral or pre-moral goods or values (life, material necessities, sociability) and minimize pre-moral evils (or disvalues)? Is this basically consequentialism, or is there a real issue here about the inherently incomplete or flawed nature of all human actions?
3. It is ever possible that we can be oriented to the good in a basic or fundamental way apart from our actions—or more precisely, beyond what our actions have the capacity to communicate?