If a moral dilemma is considered that in order to do the right thing, one has to do the wrong thing. Immanuel Kant is the most famous philosopher who said moral dilemmas are not possible. He said that moral rules can conflict, but the duties they prescribe in specific, practical cases cannot. This is based on his “categorical imperative,” in which he states that all actions should be committed in accordance with the idea that they will become universal law.” So, his example is the murderer at the door. The murderer asks the host if his next victim is inside. The host knows that the next victim is inside. Should he tell the truth or lie and keep the guest safe. Kant says that telling the truth corresponds to the categorical imperative. I’ve seen this as interpreted that Kant is making a point about universal (transcendent) morality as a guiding principle, but I’m betting he would lie to the murderer. If Kant doesn’t think there are genuine moral dilemmas, maybe he would concede that there are practical or situational moral dilemmas. I don’t know.
Both Sartre and James seem to agree that moral dilemmas exist. Sartre questions the ability of reason to come to a definitive moral conclusion. James notes the belief in a divinity encourages the one faced with the moral dilemma and thus, at least supposes the possibility of solving the dilemma, but I think his claim is still that moral dilemmas exist. The limits of human understanding and specific situations cannot practically overcome moral dilemmas.