 On Putnam’s version of the brain-in-a-vat hypothesis, the contents of the universe now and always have been relatively few. There have existed and now exist only brains in vats of nutrients and the supercomputers that send and receive messages to and from each brain. Putnam’s hypothesis assumes that each human (and each sentient creature) that exists or has ever existed is one of the brains in the vats. The supercomputers are so clever that their electronic interactions with the brains result in exact duplications of the mental lives and histories of each person whose brain is in a vat. Thus I, you, indeed we (all human beings) are brains in a vat on this hypothesis. Let us call a brain in a vat of this sort a ‘BIV’.