 The problem of intentionality is the problem of explaining what it is in general for mental states to have content, as well as the particular conditions responsible for specific variations in content. The difficulty of providing such an account lies in explaining why mental states often seem to violate familiar entailment patterns (whether or not we take such violations to be criterial of intentionality). To begin with, the content of many mental states does not correspond with what is in the world: what we imagine may not exist, our beliefs may be false, our desires may go unfulfilled. To put it more paradoxically, a mental state may be about something, even if there isn’t any such thing in the world. This is one of a number of peculiarities that prove difficult to account for, and which are sometimes thought to pose a particular stumbling block for naturalistic approaches to the mind. As Wittgenstein once quipped, you can’t hang a man unless he is there, but you can look for him even if he’s not, or even if he does not exist at all (Philosophical Investigations 1.133, §462). There are other peculiarities as well, concerning our ability to focus selectively on certain aspects of objects, without having others in mind. For example, while I cannot greet a person without greeting a person of some particular height, I can think of a person without thinking of a person of any particular height. I can also entertain different attitudes to the same object at the same time, depending on the aspect under which I consider it. So I might believe that the Morning Star is a star but that Venus is not one, despite the fact that Venus is the Morning Star; yet for just the same reason, we cannot land a space probe on the one without thereby landing it on the other. These and other difficulties form a loose family of phenomena that give rise to the problem of intentionality. Different philosophers may regard these phenomena differently, perhaps focusing on some but not others, or even excluding some as not belonging together with the rest. A philosophical history should be generous about such differences: what is important philosophically is that a philosopher recognizes that some of them pose a difficulty, at least prima facie, in accounting for mental states. (For further discussion of the methodology, see Caston 2001)