Nonmonotonic inference

Frankish, Keith (2006). Nonmonotonic inference. In: Brown, K ed. Encyclopedia of Language and Linguistics (2nd ed), Volume 8. Oxford: Elsevier, pp. 672–675.



In most logical systems, inferences cannot be invalidated simply by the addition of new premises. If an inference can be drawn from a set of premises S, then it can also be drawn from any larger set incorporrating S. The truth of the original premises guarantees the truth of the inferred conclusion, and the addition of extra premises cannot undermine it. This property is known as monotonicity.(The term is a mathematical one; a monotonic sequence is one whose terms increase but never decrease, or vice versa.) Nonmonotonic inference lacks this property. The conclusions drawn are provisional, and new information may lead to the withdrawal of a previous conclusion, even though none of the original premises is retracted.

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