as accurately as possible. The effect was to partially encode in the values of
the static evalution's parameters the knowledge gained by dynamically
searching the tree. In short, the idea was to "flatten" the complex dynamic
evaluation method into the much simpler and more efficient static evalua-
tion function.
There is a rather nice recursive effect here. The point is that the
dynamic evaluation of any single board position involves looking ahead a
finite number of moves-say seven. Now each of the scads of board posi-
tions which might turn up seven turns down the road has to be itself
evaluated somehow as well. But when the program evaluates these posi-
tions, it certainly cannot look another seven moves ahead, lest it have to
look fourteen positions ahead, then twenty-one, etc., etc.-an infinite re-
gress. Instead, it relies on static evaluations of positions seven moves ahead.
Therefore, in Samuel's scheme, an intricate sort of feedback takes place,
wherein the program is constantly trying to "flatten" look-ahead evaluation
into a simpler static recipe; and this recipe in turn plays a key role in the
dynamic look-ahead evaluation. Thus the two are intimately linked to-
gether, and each benefits from improvements in the other in a recursive
way.
The level of play of the Samuel checkers program is extremely high: of
the order of the top human players in the world. If this is so, why not apply
the same techniques to chess? An international committee, convened in
1961 to study the feasibility of computer chess, including the Dutch Inter-
national Grandmaster and mathematician Max Euwe, came to the bleak
conclusion that the Samuel technique would be approximately one million
times as difficult to implement in chess as in checkers, and that seems to
close the book on that.
The extraordinarily great skill of the checkers program cannot be
taken as saying "intelligence has been achieved"; yet it should not be
minimized, either. It is a combination of insights into what checkers is, how
to think about checkers, and how to program. Some people might feel that
all it shows is Samuel's own checkers ability. But this is not true, for at least
two reasons. One is that skillful game players choose their moves according
to mental processes which they do not fully understand-they use their
intuitions. Now there is no known way that anyone can bring to light all of
his own intuitions; the best one can do via introspection is to use "feeling"
or "meta-intuition"-an intuition about one's intuitions-as a guide, and
try to describe what one thinks one's intuitions are all about. But this will
only give a rough approximation to the true complexity of intuitive
methods. Hence it is virtually certain that Samuel has not mirrored his own
personal methods of play in his program. The other reason that Samuel's
program's play should not be confused with Samuel's own play is that
Samuel does not play checkers as well as his program-it beats him. This is
not a paradox at all-no more than is the fact that a computer which has
been programmed to calculate 7T can outrace its programmer in spewing
forth digits of 7T.
Artificial I ntelligence: Retrospects 605