Can Digital Computers Think? (1951)

The lecture ‘Can Digital Computers Think?’ was broadcast on BBC Radio on 15 May 1951, and was repeated on 3 July of that year. (Sara Turing relates that Turing did not listen to the Wrst broadcast but did ‘pluck up courage’ to listen to the repeat.) Turing’s was the second lecture in a series with the general title ‘Automatic Calculating Machines’. Other speakers in the series included Newman, D. R. Hartree, M. V. Wilkes, and F. C. Williams. Turing’s principal aim in this lecture is to defend his view that ‘it is not altogether unreasonable to describe digital computers as brains’, and he argues for the proposition that ‘If any machine can appropriately be described as a brain, then any digital computer can be so described’. The lecture casts light upon Turing’s attitude towards talk of machines thinking. In Chapter 11 he says that in his view the question ‘Can machines think?’ is ‘too meaningless to deserve discussion’ (p. 449). However, in the present chapter he makes liberal use of such phrases as ‘programm[ing] a machine . . . to think’ and ‘the attempt to make a thinking machine’. In one passage, Turing says (p. 485): ‘our main problem [is] how to programme a machine to imitate a brain, or as we might say more briefly, if less accurately, to think.’ He shows the same willingness to discuss the question ‘Can machines think?’ in Chapter 14. Turing’s view is that a machine which imitates the intellectual behaviour of a human brain can itself appropriately be described as a brain or as thinking. In Chapter 14, Turing emphasizes that it is only the intellectual behaviour of the brain that need be considered (pp. 494–5): ‘To take an extreme case, we are not interested in the fact that the brain has the consistency of cold porridge. We don’t want to say ‘‘This machine’s quite hard, so it isn’t a brain, and so it can’t think.’’ ’ It is, of course, the ability of the machine to imitate the intellectual behaviour of a human brain that is examined in the Turing test (Chapter 11).