I’m an internalist, which, in this context, means that I think that we can account for any difference between the truth conditions of two individuals’ beliefs (or between the satisfaction conditions of their desires, etc.) by reference to a difference between those individuals’ intrinsic features (roughly, features that each individual has logically independently of his or her history or environment).
I defend internalism here. More recently, in Chapter 11 of Sensorama, I argue that one’s intentional features reduce to one’s phenomenal dispositions (dispositions to have one sort of conscious experience upon having another sort of conscious experience).