We propose causal agency models for representing and reasoning about ethical dilemmas. We find that ethical dilemmas, although they appear similar on the surface, differ in their formal structure. Based on their structural properties, as identified by the causal agency models, we cluster a set of dilemmas in Type 1 and Type 2 dilemmas. We observe that for Type 1 dilemmas but not for Type 2 dilemmas a utilitarian action does not dominate the possibility of refraining from action thereby constituting a conflict. Hence, we hypothesize, based on the model, that Type 1 dilemmas are perceived as more difficult than Type 2 dilemmas by human reasoners. A behavioral study where participants rated the difficulty of dilemmas supports the models' predictions.