Sometimes we know all of the facts and every value with perfect accuracy. More often in life things are uncertain and we are used to reasoning with uncertainty. Computer systems are built over exact values, so AI often has to be more complex to deal with uncertainty. Sometimes this can be encoded in probabilities and can use Bayes Theorem or statistical techniques, although these usually require precise values for probabilites! It is also possible to use fuzzy logic or certainty factors which attempt to model, in different ways, the blurred buundaries between truth, falsity and our incomplete knowledge in between.
Defined on page 40
Used on Chap. 3: pages 40, 44, 51, 52; Chap. 12: page 267; Chap. 15: page 364
Also known as uncertain reasoning