 Two clarifications are in order. First, we will elaborate on the “significant respects” in which a mental state has to resemble another mental state in due course (see, in particular,  section 3).  For the moment, it will suffice to mention some relevant dimensions of resemblance: similar functional role; similar content; similar phenomenology; similar neural basis (an important discussion of this topic is Fisher 2006). Second, RES-1 defines “mental simulation” as a dyadic relation between mental states (the relation being a mental simulation of). However, the expression “mental simulation” is also often used to pick out a monadic property of mental states —the property being a simulated mental state (as will become clear soon, “simulated mental state” does not refer here to the state which is simulated, but to the state that does the simulating). For example, it is common to find in the literature sentences like “M* is a mental simulation”. To avoid ambiguities, we shall adopt the following terminological conventions: