In deontic logic, an obligation that violates some more primitive obligation. An example of a contrary-to-duty obligation is the case of the ‘gentle murderer’; that it is obligatory that one not kill seems true, but it also seems true that if one is to kill, that one is obligated to (at the least) do so without inflicting suffering, i.e., one is obliged to ‘kill gently’. There are many approaches with respect to the correct formalization of contrary-to-duty reasoning, i.e., reasoning about contrary-to-duty obligations.