行為者的意圖與行為的可允許性相關嗎？有些不允許做出的行為，若非行為者的意圖不良，就會是可允許做的行為嗎？傳統上，「雙果說」是主張意圖相關的典型學說，依此學說，傷害是被意圖的（不論傷害是作為目的或是作為手段而被意圖），與傷害並非被意圖而只是被預見的附帶結果，兩者在決定行為的可允許性上是有差別的。雙果說可以解釋為什麼在戰爭時期，恐怖轟炸是不允許的，但戰術轟炸卻是可允許的，即使兩項行為都同樣傷及無辜，造成平民的死傷。雙果說也可以解釋為什麼在失控電車的情境中，為了避免電車撞擊軌道上的五名工人，使其轉軌而撞擊支道上的一名工人，這樣的行為是可允許的；然而，同樣為了避免電車撞擊軌道上的五名工人，將天橋上的一名壯漢丟落軌道以阻擋電車撞擊五名工人的行為卻是不可允許的。雖然雙果說的解釋符合一般人的道德直覺，仍有許多哲學家反對其有效性，乃至於反對其意圖相關的主張。本課程將透過有代表性之哲學家們的論述，尤其著重於史坎楞的想法，檢視並且釐清行為者的意圖在行為之對錯評判上所扮演的角色。
Is the intention with which one acts relevant to the permissibility of one’s action? Can an agent’s bad intention in performing an act make it impermissible that would otherwise have been permissible? Traditionally, the doctrine of double effect (DDE) has been characterized as claiming, among other things, that intention is relevant to permissibility. According to DDE, the distinction between intending harm (as a means or as an end) and bringing about harm as a foreseen but unintended side effect of one’s action is morally significant in determining the permissibility of one’s action. DDE has the merit of being able to explain why the following contrasting cases obtain: in wartime terror bombing is impermissible; tactical bombing, by contrast, is permissible, even if both kill innocent people and cause civilian casualties. DDE can also explain why the following two cases differ in terms of permissibility: one may divert a runaway trolley into a side track, colliding with one workman, in order to save five workmen who are on the main track. By contrast, one may not push a large man, who happens to be on the bridge, down into the track in order to stop a runaway trolley from running over five workmen who are on the track. Although DDE, along with the explanation it provides, agrees with most people’s moral intuitions, a number of philosophers doubt its validity to the extent that they object to the intention-relevant thesis. Drawing on their arguments against DDE, in particular on T. M. Scanlon’s recent work, we will, in this course, not only address the related issues, but also critically examine the role one’s intention plays in affecting the permissibility of one’s action.