Simulation, if used as a way of becoming aware of other people's mental states, is the joint exercise of imagination and attribution. If A simulates B, then (1) A attributes to B the mental state in which A finds herself at the end of a process in which (2) A has imagined being in B's situation. Although necessary, imagination and attribution are not sufficient for simulation: the latter occurs only if (3) the imagination process grounds or justifies the attribution. Depending on the notion of justification we use to make sense of the idea that an episode of imagining serves as a reason for attributing a mental state, the shape of the debate and the options it offers look very different. Reconfiguring the discussion in this way, we claim, shifts the focus of the simulation versus theory-theory debate to a question located in epistemology.