Turing did not claim that the human mind really is a digital computer. More modestly, he proposed that digital computers might one day qualify in human eyes as machines endowed with "mind". However, it was not long before philosophers (most notably Hilary Putnam) took what seemed to be the next logical step—arguing that the human mind itself is a digital computer, or at least that certain mental "modules" are best understood that way. Noam Chomsky rose to prominence as one of the most audacious champions of this 'cognitive revolution'. Language, he proposed, is a computational 'module' or 'device' unique to the human brain. Previously, linguists had thought of language as learned cultural behaviour: chaotically variable, inseparable from social life and therefore beyond the remit of natural science. The Swiss linguist Ferdinand de Saussure, for example, had defined linguistics as a branch of 'semiotics', this in turn being inseparable from anthropology, sociology and the study of man-made conventions and institutions. By picturing language instead as the natural mechanism of 'digital infinity', Chomsky promised to bring scientific rigour to linguistics as a branch of strictly natural science. In the 1950s, phonology was generally considered the most rigorously scientific branch of linguistics. For phonologists, "digital infinity" was made possible by the human vocal apparatus conceptualised as a kind of machine consisting of a small number of binary switches. For example, "voicing" could be switched 'on' or 'off', as could palatisation, nasalisation and so forth. Take the consonant [b], for example, and switch voicing to the 'off' position—and you get [p]. Every possible phoneme in any of the world's languages might in this way be generated by specifying a particular on/off configuration of the switches ('articulators') constituting the human vocal apparatus. This approach became celebrated as 'distinctive features' theory, in large part credited to the Russian linguist and polymath Roman Jakobson. The basic idea was that every phoneme in every natural language could in principle be reduced to its irreducible atomic components—a set of 'on' or 'off' choices ('distinctive features') allowed by the design of a digital apparatus consisting of the human tongue, soft palate, lips, larynx and so forth. Chomsky's original work was in morphophonemics. During the 1950s, he became inspired by the prospect of extending Roman Jakobson's 'distinctive features' approach—now hugely successful—far beyond its original field of application. Jakobson had already persuaded a young social anthropologist—Claude Lévi-Strauss—to apply distinctive features theory to