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11
Case Study: Other Ways of Thinking
The discussion in previous chapters demonstrated how thinking supports intelligent
behavior in a variety of domains, including puzzles, visual scenes, English sentences,
actions, and games. Thinking uses what is known, and across the domains, the knowl-
edge varied, but the thinking procedure was always the same: back-chaining. Even
with complex extensions, like situations and fluents or minimax, the thinking proce-
dure remained the same. This chapter, however, considers
other ways
of thinking, that
is to say, other ways of using what is known.
These new modes of thinking can be illustrated with a simple example. Consider
the following four sentences:
1.
If X is a polar bear, then X is white.
2.
Thornton is a polar bear.
3.
Thornton is white.
4.
If X is a swan, then X is white.
From (1) and (2), the sort of thinking considered so far would allow (3) to be con-
cluded, which is a logical entailment of (1) and (2). This sort of reasoning is often
called
deduction
: from (1) and (2), one can deduce (3).
But suppose only (1) and (4) are known. Nothing at all is known about the indi-
vidual, Thornton. If he were actually observed to be white, one might
conjecture
that
he is a polar bear, since it is known that polar bears are white. This sort of thinking
is not deductive; it does not come with the guarantee of logical entailment. Thornton
might be a swan or something completely different. Nonetheless, the conjecture that
Thornton is a polar bear accounts for the color, as does the conjecture that he is a
swan. This type of nondeductive thinking was called
abduction
by the philosopher
C. S. Peirce: from (1) and (3), one can abduce (2). This is the sort of reasoning that
underlies
explanation
: according is what is known, Thornton being a polar bear would
explain his being white.
Now assume that at first only (2) and (3) are known. Nothing at all is known about
the color of polar bears or of swans. But then imagine (5) and (6) are observed:
