Inference to the Best Explanation is a kind of abductive reasoning identified by Gilbert Harman in 1965 ¹. He called it abductive reasoning, but Harman's definition of abduction did not correspond exactly to Charles Sanders Peirce's triple of Deduction, Induction, and Abduction.

Peirce had himself noted that all thinkers infer explanations - that is, hypotheses that might explain - various phenomena.

One of the classic examples is how to explain wet grass. If the grass is wet, it probably rained. Rain is the best explanation for wet grass, especially in Peirce's New England. But it need not be the best explanation in Arizona at the height of the dry season, where automatic sprinkler systems might be the best explanation for wet grass - especially if the grass is wet but the street is dry.

Peircean abduction is the free creation of hypotheses that generate predictions which can be tested by further observations. For example, the sprinkler hypothesis suggests looking at the street. Observing the street to be dry provides experimental confirmation of the sprinkler hypothesis relative to the rain hypothesis.

Gilbert Harman says:

"The inference to the best explanation" corresponds approximately to what others have called "abduction," the method of hypothesis," "hypothetic inference," "the method of elimination," "eliminative induction," and "theoretical inference."

I prefer my own terminology because I believe that it avoids most of the misleading suggestions of the alternative terminologies.

In making this inference one infers, from the fact that a certain hypothesis would explain the evidence, to the truth of that hypothesis. In general, there will be several hypotheses which might explain the evidence, so one must be able to reject all such alternative hypotheses before one is warranted in making the inference. Thus one infers, from the premise that a given hypothesis would provide a "better" explanation for the evidence than would any other hypothesis, to the conclusion that the given hypothesis is true.