A source of epistemic justification can be either preservative or generative, in that it can either just preserve justification that was provided by some other source or generate justification on its own. This paper asks what is required for generationism about memory to be true and argues that there are rather demanding conditions that a case of memory justification needs to satisfy in order to count as epistemically generative in a substantive sense. By considering a parallel argument for epistemically generative cases of imagination and drawing from empirical data on event completion, we argue that there are such cases of memory justification because the way in which memory processes fill in the content of event memories suggests that memory is fit to provide justification about past events that is not due to a source other than memory.