According to the Doctrine of Double Effect (DDE), there is a morally significant difference between (i) the consequences of an action that were intended by the agent and (ii) the consequences that were not intended, but are merely foreseen side-effects of the action.
More precisely, according to the DDE, if the consequences of an action include a state of affairs S, and S is in the relevant way a bad state of affairs, then (other things equal) the action is worse if it is the successful execution of an intention to bring about this state of affairs S than if S is merely foreseen (and not intended) by the agent. Being the successful execution of a bad intention of this sort is a bad feature of an action – the sort of feature that can make the action impermissible, or can at least make an impermissible action more seriously wrong than it would otherwise be.
In my view, the DDE is entirely true. But the DDE has been attacked on many fronts. One of these attacks certainly raises a fundamental problem that any full defence of the DDE must solve – namely, the “closeness problem”, which was originally raised by H. L. A. Hart in “Intention and Punishment”, and has since then been discussed by many philosophers, such as Philippa Foot, Warren Quinn, and Jonathan Bennett, among others.
More recently, however, a different sort of attack has been launched by Judith Thomson (“Self-Defense” in Philosophy & Public Affairs 1991, and “Physician-Assisted Suicide” in Ethics 1999). This attack on the DDE has now received a whole-hearted endorsement in T. M. Scanlon’s book Moral Dimensions (Harvard UP, 2008). However, Thomson’s attacks on the DDE seem to me to be completely misguided. In this post, I shall examine one of her objections, and then I shall explain what is wrong with it.