On one interpretation, Jaspers’ discussion of imaginative understanding explains how we know causal relations between psychological states. Cognitive neuroscience models of delusions typically aim at characterizing the organic disturbance that underlies the ‘primary delusion’; then, it’s assumed, mentalistic causation takes over and generates the other symptoms. No account is given of the biological underpinning of psychological causation. Imaginative understanding is not well-described by ‘simulation’ models. Simulation theory is predictive and does not attempt to find causation. Imagination here is best understood as correlative with the idea of a psychological process; imaginative understanding of psychological processes drives our ordinary conception of mental causation. We know roughly what a psychological process is and what a biological process is.But there seems to be no presumption we can map one onto the other. I review the options here and something of their implications for how we think about mind and brain in psychiatry.