  In the philosophy of mind, the phrase “methodological individualism” is commonly associated with a claim made by Jerry Fodor concerning the individuation of psychological states (1980, 1987, 42). It is important to emphasize that Fodor’s use of the term has nothing in common with its traditional use in the philosophy of social science. Fodor introduces it by way of a distinction between “methodological individualism” and “methodological solipsism.” His goal is to deal with variations on the twin-earth problem, introduced by Hilary Putnam. The question is whether an individual with a belief about water on earth, where water is made up of H2O, has the same belief as an individual with a belief about water in a parallel universe, where water has the same appearance and behavior, but happens to be made up of XYZ. The “externalist” is one who says that they are not the same, whereas an “internalist” like Fodor wants to say that they are – speaking roughly, that the content of beliefs is determined by what is in the agent’s head, and not what is in the world.