How Outlandish Can Imaginary Cases Be?

It is common in moral philosophy to test the validity of moral principles by proposing counter-examples in the form of cases where the application of the principle does not give the conclusion we intuitively find valid. These cases are often imaginary and sometimes rather ‘outlandish’, involving ray guns, non-existent creatures, etc. I discuss whether we can test moral principles with the help of outlandish cases, or if only realistic cases are admissible. I consider two types of argument against outlandish cases: 1) Since moral principles are meant for guiding action in this world, cases drawn from other worlds are irrelevant. 2) We lack the capacity to apply our intuitive moral competence to outlandish cases. I argue that while the first approach is importantly flawed, the second approach is plausible, not because our moral competence per se is limited to cases from this world, but because we lack the capacity to imagine outlandish cases, and we cannot apply our moral competence to a case we fail to imagine properly.