The complaint that philosophy makes no progress is usually supported by pointing out that its questions are the ones Plato asked, which is true and proves less than it appears to. Every field that succeeds in answering a question definitively exports it: natural philosophy became physics, and the study of mind has been steadily transferring its tractable portions to psychology and neuroscience for a century. What remains in the parent discipline is by construction the residue that has resisted formalisation, so the appearance of stagnation is partly an artefact of how the boundary is drawn. This defence is sound and incomplete, since it does not show that the residue is tractable at all, and the possibility that some questions are permanently unanswerable is not one the discipline has examined with much enthusiasm.