 For example, a still very common idea, often attributed to John Locke and openly embraced by Jerry Fodor in the nineteen seventies, is that interpersonal spoken communication works by speakers’ translation of their internal mental vocabularies into sounds followed by hearers’ re-translation into their own internal vocabularies. Again, Descartes considered himself able to talk to himself about his experiences while claiming to be justified in saying that he does not know (or not until he has produced a reassuring philosophical argument) anything at all about an external world conceived as something independent of them. And he and others have thought: while I may make mistakes about the external world, I can infallibly avoid error if I confine my judgments to my immediate sensations. (Compare The Principles of Philosophy, I, 9.) Again, many philosophers, including John Stuart Mill, have supposed there to be a problem of other minds, according to which I may reasonably doubt the legitimacy of applying, say, sensation-words to beings other than myself.