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‘foil’—serves as a point of comparison. The judge has to try and figure out which of the other
two participants is which, human or non-human, simply by chatting with them via a keyboard
(Fig. 25.2). The foil’s job is to help the judge make the right identification. A number of chat
sessions are run using different judges and different foils, and if the judges are mistaken often
enough about which contestant is which, the computer (or alien) has passed the test.^23
Turing imagined conducting these conversations via an old-fashioned teleprinter, but nowa-
days we would use email or text messages. Apart from chatting, the judges must be kept strictly
out of contact with the contestants—no peeping is allowed. Nor, obviously, are the judges
allowed to measure the candidates’ magnetic fields, or their internal temperatures, or their
processing speeds. Only Q & A is permitted, and the judges must not bring any scientific equip-
ment along to the venue.
Justifying his test, Turing pointed out that the judges can use keyboard chat to probe the
computer’s skill in almost all fields of human endeavour. His examples included mathematics,
chess, poetry, and flirting. He said: ‘The question and answer method seems to be suitable
for introducing almost any one of the fields of human endeavour that we wish to include’.^24
Turing added drolly, ‘We do not wish to penalise the machine for its inability to shine in beauty
competitions’, making the point that his question and answer test excludes irrelevant factors.^25
No questions are barred—the computer must be able to deal fair and square with anything
the judge throws at it. But in order to avoid loading the dice against the computer, Turing stipu-
lated that the judges ‘should not be expert about machines’.^26 He also said that the computer is
allowed to use ‘all sorts of tricks’ to bring about a wrong identification.^27 Smart moves for the
computer are to reply ‘No’ in response to ‘Are you a computer?’, and to follow a request to mul-
tiply one huge number by another with a long pause and an incorrect answer—but a plausibly
incorrect answer, not simply a random number. In order to fend off especially awkward ques-
tioning, the computer might even pretend to be from a different (human) culture than the
judge. In fact, it is a good idea to select the test personnel so that, from time to time, the judge
and the foil are themselves from different cultures.^28
figure 25.1 Freddy, an early implementa-
tion of Turing’s concept of a child machine.
Image from Artificial Intelligence, Informatics,
University of Edinburgh.