ABDUCTION

Latin abductio, “action of taking”, by an outwardly directed movement (see below, meaning 2).

1. Abduction as Inference from Facts to Hypothesis

The concept of abduction was introduced to modern philosophy by philosopher Charles Sanders Peirce. According to Peirce, there are two kinds of inferences: deductive inference and abductive inference or abduction. Abduction starts from the observation of a fact that is “contrary to what we should expect” (Peirce ([1958], § 202), that is to say, a fact that does not fit into an available explanatory system. Abduction is a process by which one proposes a hypothesis accounting for this new fact.
This hypothesis is not the product of the applying a “discovery algorithm”, but rather the fruit of a creative process. “Abduction is, after all, nothing but guessing” (Peirce [1958], § 219).

Abduction is not an issue in logic, but rather a scientific method (id., Chap. 6). Scientific work consists of proposing, on the basis of facts, plausible hypotheses “suggested” by these facts. Abduction is the first step in this process.
The practice of abduction is not guided by logical rules but rather by general principles, such as the principle of exclusion of so-called metaphysical hypotheses, that is to say, hypotheses that would have no experimental consequences, or the principle according to which every fact has an explanation. An abductive hypothesis is interesting “if it seems to make the world reasonable” (id., §202).

Unlike abduction, which starts with facts and searches for theory, the Peircean deduction starts with a theory in search of facts; that is, it seeks to identify the crucial experimental consequences of a hypothesis.

Rather than being a form of deduction or induction, argumentation should be seen as a form of abduction. For example, when the light is on, “I abduct”, that is, I hypothesize, that someone is in the room; however, this hypothesis still needs to be verified, see probable, plausible, true.

Woods redefines abductions as “responses to ignorance-problems. An agent has an ignorance-problem in relation to an epistemic target that cannot be hit by the cognitive resources presently at his command, or within easy and timely reach of it” (Woods, 2009; Gabbay & Woods, 2005). The study of argument as an abductive process has proved especially fruitful in the fields of medicine, science and law (Walton 2004).

2. Abduction as Reduction of Uncertainty

In its Peircean sense, abduction is a type of inference by which one arrives at a hypothesis that accounts for a given fact. Aristotle defines abduction as a kind of dialectical syllogism (Aristotle, PA, II, 25), in which the major premise is true and the minor merely probable, and, consequently, the conclusion also probable. Without the minor, the conclusion alone is more improbable than the minor. Therefore, the minor strengthens the relative acceptability of the conclusion. This situation recalls the Ciceronian definition of argumentation, see argumentation 1.

For example, if the question is: “can virtue be taught?” we can reason as follows:

A true premise: it is clear that science can be taught.
A doubtful premise: virtue is a science.
Conclusion: virtue can be taught.

Though uncertain, the veracity of the second premise is still less in doubt than the conclusion “virtue can be taught”. Therefore, this second premise may serve as an argument for the conclusion. We find this montage in speeches such as:

Citizenship can be taught.
Citizenship is essentially a set of social knowledge and practices.
Knowledge can be taught and all practical skills can be improved by teaching. Therefore, citizenship can be taught.

Arguments function “for want of better”. Reducing uncertainty modifyies the epistemic status of a belief. This is a logic not of elimination but of reduction of doubt and uncertainty, see default reasoning.