Plausible Reasoning and First-Order Plausible Logic
This work provides a formal logical framework for plausible reasoning, which is relevant for AI and knowledge representation, but the novelty is incremental as it builds on existing logical approaches.
The authors propose a first-order logic called Plausible Logic (PL) that satisfies 12 of 17 principles for plausible reasoning without using probabilities, correctly handling several key examples. PL is claimed to be the only such logic with 8 reasoning algorithms.
Defeasible statements are statements that are likely, or probable, or usually true, but may occasionally be false. Plausible reasoning makes conclusions from statements that are either facts or defeasible statements without using numbers. So there are no probabilities or suchlike involved. Seventeen principles of logics that do plausible reasoning are suggested and several important plausible reasoning examples are considered. There are 14 necessary principles and 3 desirable principles, one of which is not formally stated. A first-order logic, called Plausible Logic (PL), is defined that satisfies all but two of the desirable principles and reasons correctly with all the examples. As far as we are aware, this is the only such logic. PL has 8 reasoning algorithms because, from a given plausible reasoning situation, there are different sensible conclusions. This article is a condensation of my book `Plausible Reasoning and Plausible Logic' (PRPL), which is to be submitted. Each section of this article corresponds to a chapter in PRPL, and vice versa. The proofs of all the results are in PRPL, so they are omitted in this article.