John L. Pollock

Nomic Probability and the Foundations of Induction, Oxford, 1990 was Pollock's deep investigation of the relationship between defeasible reasoning and the estimation of probability from frequencies (direct inference of probability). It is a maturation of ideas originally found in a 1983 Theory and Decision paper. This work must be compared to Henry E. Kyburg's theories of probability, although Pollock believed that he was theorizing about a broader variety of statistical inferences.

Pollock became known as "Mr. Defeasible Reasoning" among philosophers in the two decades before his death. In artificial intelligence, where non-monotonic reasoning had caused intellectual upheaval, scholars sympathetic to Pollock's work held him in great esteem for his early commitment and clarity. Pollock's most direct pronouncement is the paper "Defeasible reasoning" in Cognitive Science, 1987, though his non-syntactic ideas were almost fully mature in Knowledge and Justification. Pollock traced the history of his own thinking (e.g., in a footnote in Pollock and Cruz, Contemporary Theories of Knowledge, 1999, p. 36, note 37, and elsewhere) to his first paper on epistemology, "Criteria and our knowledge of the material world," Philosophical Review 76, 1967. He thought that Roderick Chisholm had influenced his thinking on the subject, but he also said he was attempting to interpret Ludwig Wittgenstein directly, and sometimes credited Stephen Toulmin on the subject of argument. Although his work had considerable impact in the area of Artificial intelligence and law, Pollock was not himself interested much in jurisprudence or theories of legal reasoning, and he never acknowledged the inheritance of defeasible reasoning through H.L.A. Hart. Pollock also held informal logicians and scholars of rhetoric at a distance, though defeasible reasoning has natural affinities in argument.

John L. Pollock (1940–2009) was an American philosopher known for influential work in epistemology, philosophical logic, cognitive science, and artificial intelligence.

Born John Leslie Pollock in Atchison, Kansas, on January 28, 1940, Pollock earned a triple-major physics, mathematics, and philosophy degree at the University of Minnesota in 1961. In 1965, his doctoral dissertation Analyticity and Implication at the University of California, Berkeley was advised by Ernest Adams (making Pollock an intellectual descendant of Gottfried Leibniz and Immanuel Kant, through Ernest Nagel and Patrick Suppes). This dissertation contained an appendix on defeasible reasoning that would eventually blossom into his main contribution to philosophy.