Induction and Abduction

Deduction: apply general principle to infer a fact.[Examples from John Sowa, ``The Challenge of Knowledge Soup.'']

Given:  Every bird flies.  Tweety is a bird.
Infer:  Tweety flies.

Induction: assume a general principle that subsumes many facts.

Given:  Tweety, Polly, and Hooty are birds.
        Tweety, Polly, and Hooty fly.
        Fred is a bat.  Fred flies.
Assume: Every bird flies.

Abduction: guess a new hypothesis that explains some fact.

Given:  Every bird flies.  Tweety flies.
Guess:  Tweety is a bird.

Deduction is sound; induction and abduction are not sound, but essential for intelligence.

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