According to ‘internalism’, what mental states people are in depends wholly on what obtains inside their heads. This paper challenges that view without relying on arguments about the identity-conditions of concepts that make up the content of mental states. Instead, it questions the internalist’s underlying assumption that, in Searle’s words, “the brain is all we have for the purpose of representing the world to ourselves”, which neglects the fact that human beings have used their brains to devise methods for extending and enhancing the brain’s own functions, in particular for storing information externally. Although Popper draws attention to this fact, he fails to grasp its psychological implications, concluding instead that there can be knowledge “without a knowing subject”, and so repeating the internalist’s mistake. With equal justice one can conclude, absurdly, that there are ownerless plans, resolutions and shopping-lists. The paper goes on to meet possible internalist counter-arguments.