Brains encode knowledge not only about the external world but also about their own functioning. These internal self-models are critical for knowing what we would perceive, remember, and do in hypothetical and counterfactual world states (“Would I remember if I met her before?”, “Would I have noticed if someone called my name?”, “What would I have done if I didn’t know that?”). I will present results that indicate a role for such internal mental models of perception and cognition in inference about absence and epistemic pretense. In both cases, human behaviour reveals hard limits on the human capacity for reasoning about counterfactual mental states. I will argue that targeting the ways self-models are used in cognition, rather than how they appear to us upon reflection, is an important next step for the science of self-knowledge and metacognition.