The Principle of Double Effect

2. What Is the Principle of Double Effect?

Book cover: Causing Death and Saving Lives by Jonathan Glover

The Principle of Double Effect itself has had a long history of development and over this period its conditions have been fairly well standardized. There have been some recent attempts to modify it,[1] but I will not be concerned with these here. I shall rely instead on the standard formulation. The principle refers to actions in which a good effect and a bad effect will follow, and stipulates four conditions that must be satisfied for the action to be morally justifiable. These conditions are:

  1. The act itself must be morally good or at least indifferent.

  2. The agent may not positively will the bad effect but may merely permit it. If he could attain the good effect without the bad effect, he should do so. The bad effect is sometimes said to be indirectly voluntary.

  3. The good effect must flow from the action at least as immediately (in the order of causality, though not necessarily in the order of time) as the bad effect. In other words, the good effect must be produced directly by the action, not by the bad effect. Otherwise, the agent would be using a bad means to a good end, which is never allowed.

  4. The good effect must be sufficiently desirable to compensate for the allowing of the bad effect.

[New Catholic Encyclopedia 1967: vol. 4: 1021]


  1. [1] See, for example, Grisez [1970] and Geddes [1973].

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