  Turing's 1950 paper was intended for a wide readership, and its fresh and direct approach has made it one of the most frequently cited and republished papers in modern philosophical literature. Not surprisingly, the paper has attracted many critiques. Not all commentators note the careful explication of computability which opens the paper, with an emphasis on the concept of the universal machine. This explains why if mental function can be achieved by any finite discrete state machine, then the same effect can be achieved by programming a computer (Turing 1950b, p. 442). (Note, however, that Turing makes no claim that the nervous system should resemble a digital computer in its structure.) Turing's treatment has a severely finitistic flavour: his argument is that the relevant action of the brain is not only computable, but realisable as a totally finite machine, i.e. as a Turing machine that does not use any ‘tape’ at all. In his account, the full range of computable functions, defined in terms of Turing machines that use an infinite tape, only appears as being of ‘special theoretical interest.’ (Of uncomputable functions there is, a fortiori, no mention.) Turing uses the finiteness of the nervous system to give an estimate of about 109 bits of storage required for a limited simulation of intelligence (Turing 1950b, p. 455).