CHAPTER 25

Intelligent machinery

jack copeland

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his chapter explains why Turing is regarded as founding father of the field of artificial

intelligence (AI), and analyses his famous method for testing whether a computer is

capable of thought.

The first manifesto of AI

In the weeks before his 1948 move from the National Physical Laboratory to Manchester,

Turing wrote what was, with hindsight, the first manifesto of artificial intelligence (AI). His

provocative title was simply Intelligent Machinery.^1

While the rest of the world was just beginning to wake up to the idea that computers were the

new way to do high-speed arithmetic, Turing was talking very seriously about ‘programming

a computer to behave like a brain’.^2 Among other shatteringly original proposals, Intelligent

Machinery contained a short outline of what we now refer to as ‘genetic’ algorithms—algorithms

based on the survival-of-the-fittest principle of Darwinian evolution—as well as describing the

striking idea of building a computer out of artificial human nerve cells, an approach now called

‘connectionism’. Turing’s early connectionist architecture is outlined in Chapter 29.

AI and the bombe

Strangely enough, Turing’s 1940 anti-Enigma bombe was the first step on the road to modern

AI.^3 As Chapter 12 explains, the bombe worked by searching at high speed for the correct set-

tings of the Enigma machine—and once it had found the right settings, the random-looking

letters of the encrypted message turned into plain German. The bombe was a spectacularly

successful example of the mechanization of thought processes: Turing’s extraordinary machine

performed a job, codebreaking, that requires intelligence when human beings do it.

The fundamental idea behind the bombe, and one of Turing’s key discoveries at Bletchley

Park, was what modern AI researchers call ‘heuristic search’.^4 The use of heuristics—shortcuts

or rules of thumb that cut down the amount of searching required to find the answer—is still a