To a writer of the old school, whose academic training dates back to the ’50s and ’60s of the last century, working in a Latin phrase is akin to flashing a badge of one’s scholarly credentials, and the lure is strong. At one time, before the onset of the digital age, there was nothing unusual about reading the following utterance of Sherlock Holmes to Dr. Watson in Conan Doyle’s novel The Sign of the Four: “Quite so. They are in a state of extreme contraction, far exceeding the usual rigor mortis. Coupled with this distortion of the face, this Hippocratic smile, or ‘risus sardonicus,’ as the old writers called it, what conclusion would it suggest to your mind?” Here, note Holmes’s stylistic qualification, “as the old writers called it,” marking the Latin phrase as already somewhat obsolescent at the time of writing. Speaking of Holmes and the lure of Latin, here is a fresh example, meant originally for publication in the public press.

Lately, in these pages [The NY Times] and elsewhere in the media––including movies, plays, and even letters to the editor––there have been numerous mentions of and adversions to Sherlock Holmes, the fictional master detective created by Sir Arthur Conan Doyle. In Conan Doyle’s early second novel, The Sign of the Four (1890), the opening chapter is entitled “The Science of Deduction,” meant to characterize the mode of reasoning (“deduction”) that is Holmes’s stock in trade and that enables him to solve even the most abstruse cases. Indirectly, moreover, that is what the famous retort––”Elementary, my dear Watson,” by which we all know Sherlock but which he never actually utters in any of the Holmesian canon––refers to, which is his power of making correct inferences or educated guesses from seemingly unconnected pieces of evidence.

But the word “deduction” as used by Conan Doyle and all other writers before and after is actually a misnomer. The correct name for the type of reasoning at stake is “abduction,” and the distinction is far from trivial. The name was coined in 1867 by the greatest intellect the Americas have ever produced, the philosopher-scientist Charles Sanders Peirce (1839-1914), whose work in logic alone places him in the same rank as Aristotle and Leibniz.

Deduction, induction, and abduction are the three fundamental modes of reasoning that constitute the traditional syllogism of logic. Deduction proceeds from correct premisses and valid cases to reach unassailable conclusions. Thus if “All men are mortal” (premiss) and “Socrates is a man” (case), then the deduced conclusion “Socrates is mortal” follows without fail. Induction, by contrast, tests the law (premiss) by applying extant cases to it. Hence, if “Socrates is mortal” is a valid conclusion and “Socrates is a man” a valid case, then the law “All men are mortal” is valid by induction.

But––crucially––stating that something is the case is the only mode of reasoning that is fallible, since it is invariably subject to further testing, wherein its validity may or may not be borne out. Knowing that (1) all men are mortal and that (2) Socrates is mortal does not prove that (3) Socrates is a man because Socrates may turn out to be a horse or an inanimate object and not a man at all. We may guess wrong despite the evidence, although as Peirce argued, we have a propensity to guess right, otherwise we wouldn’t have survived as a species. Using Peirce’s word in its verbal form, we all have the power to abduce the truth from (typically scant) evidence. In this respect, Sherlock Holmes is only a superlatively talented exemplar of homo abducans.

All new knowledge, therefore, comes about exclusively through abduction, which is the technical logical term synonymous with the more familiar “hypothesis.” All advances in science begin as hypotheses (abductive inferences) that are borne out upon (repeated) testing. Here is how Peirce put it to the audience of his lectures on pragmatism at Harvard in 1903: “The surprising fact, C, is observed; But if A were true, C would be a matter of course. Hence, there is reason to suspect that A is true.” The verb “suspect” is particularly apt in the context of Holmes’s powers of detection. This word describes the action of the educated guess. Equally apt, accordingly, is the phrase “matter of course”. This is implicit in the opening adjective of the factitious phrase “Elementary, my dear Watson.” QED.

Peirce was so great a thinker that no university could find a place for him during his lifetime. He suffered terribly at the end, living on the charity of his friend William James and taking morphine for the trigeminal neuralgia and cancer that ultimately killed him. But just like Sherlock Holmes, who palliated his boredom with violin-playing and cocaine, Peirce will live forever in history and in our imaginations as an icon of that uniquely human cognitive capacity, abduction, to which he gave a name and Holmes embodied ne plus ultra.