Hume's Copy Principle, which accords precedence to impressions over ideas, is restricted to simple perceptions. Yet in all the conceptual analyses Hume conducts by attempting to fit an impression to a (putative) idea, he never checks for simplicity. And this seems to vitiate the analyses: we cannot conclude from the lack of a preceding impression that a putative idea is bogus, unless it is simple. In this paper I criticise several attempts to account for Hume's seemingly cavalier attitude, and offer (...) one of my own. (shrink)