ABSTRACT A striking feature of the traditional armchair method of philosophy is the use of imaginary examples: for instance, of Gettier cases as counterexamples to the justified true belief analysis of knowledge. The use of such examples is often thought to involve some sort of a priori rational intuition, which crude rationalists regard as a virtue and crude empiricists as a vice. It is argued here that, on the contrary, what is involved is simply an application of our general cognitive capacity to handle counterfactual conditionals, which is not exclusively a priori and is not usefully conceived as a form of rational intuition. It is explained how questions of metaphysical possibility and necessity are equivalent to questions about counterfactuals, and the epistemology of the former (in particular, the role of conceiving or imagining) is a special case of the epistemology of the latter. A non-imaginary Gettier case is presented in order to show how little difference it makes.