Born in Philadelphia, Chomsky was educated at the University of Pennsylvania under the linguist Zellig Harris, and after a period at the Society of Fellows at Harvard was awarded his doctorate there in 1955. He has taught at the Massachusetts Institute of Technology since 1955. Arising from his dissertation, his book Syntactic Structures (1957) is widely regarded as the most significant contribution to theoretical linguistics of the second half of the 20th century. Chomsky believes that the speed with which children master their native language cannot be explained by learning theory, but requires acknowledging an innate disposition of the mind, an unlearned, innate, and universal grammar, supplying the kinds of rule that the child will a priori understand to be embodied in examples of speech with which it is confronted. In computational terms, unless the child came bundled with the right kind of software, it could not catch on to the grammar of language as it in fact does. Cartesian Linguistics (1966) makes plain the antiempiricist, rationalist implications of this idea, however the emergence of learning theory revolving around such tools as Bayesian nets has dimmed the lustre of his argument. Earlier critics such as Ryle complained that the argument pays too little attention to the realities of imitation and practice in the learning process, and seeks to fill the gap only with ‘clouds of biological glory’, but Chomsky’s nativism is still influential in linguistics and psychology. Outside linguistics Chomsky was well-known for his opposition to the American war in Vietnam, and was at the time the leading dissident academic critic of the United States government. He has continued to be the best-known radical and dissident voice of his time in the United States. See also generative grammar, innate ideas.