 An example will clarify the matter. Suppose that I know that you desire to eat sushi, and that you believe that you can order sushi by calling Yama Sushi. To reach the conclusion that you will decide to call Yama Sushi, I only need to imagine desiring and believing what you desire and believe, and to run a simulated decision-making process in myself. No further knowledge is required to predict your decision: simulation alone will do the job. Consider, on the other hand, the situation in which I know that you took a certain drug and I want to figure out what your mental states will be. In this case—Heal says—my prediction cannot be based on mental simulation. Rather, I need to resort to a body of information about the likely psychological effects of that drug, i.e., I have to resort to a Theory of Mind (fair enough, I can also take the drug myself, but this will not count as mental simulation). This, according to Heal, generalizes to all cases in which a mental state is the input or the output of a mere causal process. In those cases, mental simulation is ineffective and should be replaced by theorizing. Still, those cases do not constitute the central part of mindreading. In fact, many philosophers and cognitive scientists would agree that the crucial component of human mindreading is the ability to reason about others’ propositional attitudes. And this is exactly the ability that, according to Heal, should be explained in term of mental simulation. This is why Heal’s proposal counts as an ST-TT hybrid, rather than the other way around.