The Stanford Encyclopedia of Philosophy (Fall 2018 Edition), Edward N. Zalta (ed.)
Here are two brief excerpts:
Moral considerations often conflict with one another. So do moral principles and moral commitments. Assuming that filial loyalty and patriotism are moral considerations, then Sartre’s student faces a moral conflict. Recall that it is one thing to model the metaphysics of morality or the truth conditions of moral statements and another to give an account of moral reasoning. In now looking at conflicting considerations, our interest here remains with the latter and not the former. Our principal interest is in ways that we need to structure or think about conflicting considerations in order to negotiate well our reasoning involving them.
Understanding the notion of one duty overriding another in this way puts us in a position to take up the topic of moral dilemmas. Since this topic is covered in a separate article, here we may simply take up one attractive definition of a moral dilemma. Sinnott-Armstrong (1988) suggested that a moral dilemma is a situation in which the following are true of a single agent:
- He ought to do A.
- He ought to do B.
- He cannot do both A and B.
- (1) does not override (2) and (2) does not override (1).
This way of defining moral dilemmas distinguishes them from the kind of moral conflict, such as Ross’s promise-keeping/accident-prevention case, in which one of the duties is overridden by the other. Arguably, Sartre’s student faces a moral dilemma. Making sense of a situation in which neither of two duties overrides the other is easier if deliberative commensurability is denied. Whether moral dilemmas are possible will depend crucially on whether “ought” implies “can” and whether any pair of duties such as those comprised by (1) and (2) implies a single, “agglomerated” duty that the agent do both A and B. If either of these purported principles of the logic of duties is false, then moral dilemmas are possible.
The entry is here.