330 | 31 COmPUTER CHESS—THE fIRST mOmENTS
Michie : ‘We talked about putting numerical values on the pieces. And we talked about
the mechanization of conditionals of the form: “If I do that, he might to do that, or
alternatively he might do that, in which case I could do this”—what today we would call
look-ahead. We certainly discussed priority of ordering according to some measurable
plausibility of the move.’
Copeland : ‘So that’s what chess programmers now call best-first?’
Michie : ‘Yes, that’s right. Our discussions of chess programming also included the idea of punish-
ing the machine in some sense for obvious blunders. And the question of how on earth it
might be possible to make this useful, beyond the pure rote-learning effects of punishment—
deleting a move from the repertoire. Which is only applicable in the early opening.’
Copeland : ‘Did Turing have any specific ideas about how to do this?’
Michie : ‘I don’t remember any in the context of chess. I do remember him later circulating a
typescript in which he had specific ideas about learning and more general varieties of learning.’
Copeland : ‘Was this at Bletchley?’
Michie : ‘At Bletchley, yes. When I say “circulating”, I know he showed a copy to me and to
Jack Good—and I suppose to one or two other associates—for our comments.’
The ‘best-first’ principle that Michie referred to involves a rule-of-thumb scoring system:
at any given point in the game, the program can use this scoring system to rank the available
moves; and it then goes on to examine the consequences of the best (highest-scoring) move
first. In an earlier conversation Michie had explained that their wartime chess discussions also
covered the ‘minimax’ principle:^6 minimax involves assuming that opponents will move so as
to maximize their gains, and the program then moves so as to minimize the losses caused by the
opponent’s expected moves. John von Neumann had investigated the minimax approach in his
groundbreaking forays into what mathematicians now call ‘game theory’, and in 1928 he had
published his fundamental ‘minimax theorem’.^7
None of this pioneering work at Bletchley Park on computer chess was published. Like
Michie, Good ‘made the mistake of thinking it was not worth publishing’, he said.^8 But once
the war came to an end in 1945, and Turing had more time to devote to the topic of machine
intelligence, statements about computer chess began to appear in his writings. He even men-
tioned chess in the ultra-serious ‘Proposed electronic calculator’, his famous 1945 report about
the ACE. He said:^9
Given a position in chess the machine could be made to list all the ‘winning combinations’ to a
depth of about three moves on either side. This . . . raises the question ‘Can the machine play
chess?’ It could fairly easily be made to play a rather bad game. It would be bad because chess
requires intelligence.
Then he added prophetically:
There are indications however that it is possible to make the machine display intelligence at the
risk of its making occasional serious mistakes. By following up this aspect the machine could
probably be made to play very good chess.
At the same time (1945) the German computer pioneer Konrad Zuse—working in com-
plete isolation in a village in the Bavarian Alps—was developing his Plankalkül programming
language, and was also thinking about chess and other forms of symbolic computation.^10 Two
years later Turing again mentioned chess, in his remarkably far-sighted 1947 Burlington House
lecture about the future of computing (see Chapter 25), predicting that it ‘would probably be