Reasoning and Representation
26.1 Nonmonotonic or Defeasible Reasoning
Those AI researchers called logicists, who favor the use of logical languages for representing knowledge and the use of logical methods for reasoning, acknowledge one problem with ordinary logic; namely, it is monotonic. By that they mean that the set of logical conclusions that can be drawn from a set of logical statements does not decrease as more statements are added to the set. If one could prove a statement from a given knowledge base, one could still prove that same statement (with the very same proof !) when more knowledge is added.
Yet, much human reasoning does not seem to work that way – a fact well noticed (and celebrated) by AI’s critics. Often, we jump to a ...