By “case,” I mean a proxy for some state of affairs, event, sequence of events, or other fact. A case may be as short as a phrase (“a promise to your dying grandfather”) or (in principle, at least) longer than War and Peace. A case may consist of words (as in the typical philosophical example) or have a more dramatic form, such as a movie, stage performance, or computer simulation. Imaginary cases plainly have an important role in contemporary ethics, especially (...) in applied or practical ethics. This paper is a systematic critique of imaginary cases in ethics (what Kant would have called a “prolegomenon” to their use). There are two main parts. The first explains what it is to imagine a case and what limits there are to what can be imagined. The limits of imagination are, in general, determined by the purpose to which the case is to be put. The second part distinguishes nine uses of imaginary cases: rhetorical; probative (subdivided into counterexample, proof of possibility, and pattern-proving); and heuristic (subdivided into illustrative, experiment in theory, insight-sharpening, commitment-mapping, and exploring reasoning process). Some of these uses are (more or less) unobjectionable (whether the particular case succeeds or fails in its objective) but some require special care or outright avoidance. I give examples of how philosophers and other ethicists would be better off if they were more cautious in their use of imaginary cases (including some classic examples, such as Nozick’s book thruster and Thompson’s famous violinist). This paper is especially concerned with the use of imaginary cases in contemporary defenses of torture. (shrink)