 This reply invited the following response (Jackson 1999). If the possibility of process-driven simulation is grounded in the similarity between the simulator and the simulated, then I have to assume that you are relevantly similar to me, when I mentally simulate your mental states. This particular assumption, in turn, will be derived from a general principle—something like “Human beings are psychologically similar”. Therefore, mental simulation is grounded in the possession of a theory. The threat of collapse is back! One reply to Jackson’s arguments is as follows (for other replies see Goldman 2006): the fact that process-driven simulation is grounded in the similarity among human beings does not entail that, in order to run a simulation, a simulator must know (or believe, or assume) that such similarity obtains; no more, indeed, than the fact that the solubility of salt is grounded in the molecular structure of salt entails that a pinch of salt needs to know chemistry to dissolve in water.