The celebrated "Twin Earth" arguments of Hilary Putnam (1975) and Tyler Burge (1979) aim to establish that some intentional states logically depend on facts external to the subjects of those states. Ascriptions of states of these kinds to a thinker entail that the thinker's environment is a certain way. It is not possible that the thinker could be in those very intentional states unless the environment is that way...