 A number of philosophers have suggested that the content of one’s beliefs depends entirely on things going on inside one’s head, and not at all on the external world, except via the effects of the latter on one’s brain. Consequently, if a genius neuroscientist were to create a molecule-for-molecule duplicate of your brain and maintain it in a vat, stimulating it artificially so that it underwent exactly the same sequence of electrical and chemical events as your actual brain, that brain would have exactly the same beliefs as you. Those who accept this position are internalists about belief content. Those who reject it are externalists.