WHAT IS ABDUCTION?

In the 1890s, the great American philosopher C. S. Peirce (1931–1958) used the term “abduction” to refer to a kind of inference that involves the generation and evaluation of explanatory hypotheses. This term is much less familiar today than “deduction,” which applies to inference from premises to a conclusion that has to be true if the premises are true. And it is much less familiar than “induction,” which sometimes refers broadly to any kind of inference that introduces uncertainty, and sometimes refers narrowly to inference from examples to rules, which I will call “inductive generalization.” Abduction is clearly a kind of induction in the broad sense, in that the generation of explanatory hypotheses is fraught with uncertainty. For example, if the sky suddenly turns dark outside my window, I may hypothesize that there is a solar eclipse, but many other explanations are possible, such as the arrival of an intense storm or even a huge spaceship.

Despite its inherent riskiness, abductive inference is an essential part of human mental life. When scientists produce theories that explain their data, they are engaging in abductive inference. For example, psychological theories about mental representations and processing are the result of abductions spurred by the need to explain the results of psychological experiments. In everyday life, abductive inference is ubiquitous, for example when people generate hypotheses to explain the behavior of others, as when I infer that my son is in a bad mood to explain a curt response to a question.