I argue that the function of episodic memory is to store information about the past, against the orthodox view that it is to support imagining the future. I show that episodic memory is epistemically generative, allowing organisms to learn from past events retroactively. This confers adaptive benefits in three domains: reasoning about the world, skill, and social interaction. Given the role of evolutionary perspectives in comparative research, this argument necessitates a radical shift in the study of episodic memory in nonhumans.