 Faced with the issue of accounting for the apparent phenomena of mind-body interaction, those who subscribed to “Cartesian interactionism” (following Williams 1978, 287; Williams actually describes the situation as a “scandal”) held that the causal interaction is not merely apparent but real. In other words, changes in the body and mind really bring about changes in each other. But many found this position deeply unsatisfying. Some raised questions about whether it was intelligible that such radically distinct substances with nothing in common causally interacted, and others questioned whether such a view was consistent with the view that was gaining popularity, namely, that the material universe is causally closed and governed solely by physical laws of nature. Whether or not Descartes actually held this interactionist position is, as discussed earlier, a matter of controversy, but even in Descartes’ time the list of the critics of interactionism was a long one.