Holmesian fallacy

[[File:Paget holmes.png|thumb|right|165px|John H. Watson and Sherlock Holmes from an 1893 illustration of ''The Greek Interpreter'']]
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A '''Holmesian fallacy''' (also '''Sherlock Holmes fallacy''' or '''process of elimination fallacy''') is a [[logical fallacy|logical error]] in which an explanation is believed to be true because alternate explanations seem impossible, even though not all plausible alternatives have been considered. It is an [[informal fallacy]] and can be seen as a misuse of [[abductive reasoning]]; with Holmesian fallacy overextending it into a deductive-like certainty — i.e. treating abduction as [[deduction]].<ref name="Bird2005">Bird, Alexander, 'Abductive Knowledge and Holmesian Inference', in Tamar Szabó Gendler, and John Hawthorne (eds), Oxford Studies In Epistemology (Oxford, 2005; online edn, Oxford Academic, 31 Oct. 2023), https://doi.org/10.1093/oso/9780199285891.003.0001, accessed 25 Oct. 2025.</ref><ref name="Hanzal2024">Hanzal, T. Deduction, Abduction, and Creativity. Acta Anal 39, 163–182 (2024). https://doi.org/10.1007/s12136-023-00555-2</ref>

==Alternate names==
*far-fetched hypothesis
*arcane explanation

==Explanation==
The Holmes Method is illustrated by the quote from "{{wpl|The Adventure of the Blanched Soldier}}",<ref group=note>Similar quotes appear in Chapter 6 of the 1890 Sherlock Holmes novel ''{{wpl|The Sign of the Four}}'' ("How often have I said to you that when you have eliminated the impossible, whatever remains, however improbable. must be the truth?"), the 1892 Sherlock Holmes short story "{{wpl|The Adventure of the Beryl Coronet}}" ("It is an old maxim of mine that when you have eliminated the impossible, whatever remains, however improbable, must be the truth."), and the 1902 Sherlock Holmes short story "{{wpl|The Adventure of the Bruce-Partington Plans}}" ("We must fall back upon the old axiom that when all other contingencies fail, whatever remains, however improbable, must be the truth.")</ref> a 1926 Sherlock Holmes short story:
{{quotebox|"When you have eliminated all which is impossible, then whatever remains, however improbable, must be the truth." —Sherlock Holmes}}

This quote illustrates a principle of elimination in reasoning. However, taking it literally as a strict method would require knowing every possible explanation and correctly disproving all but the true one — something rarely possible in practice.<ref name="Bird2005"/><ref name="Johnson-Laird">Johnson-Laird, Philip N., 'Sherlock Holmes's Method: Abduction', How We Reason (Oxford, 2008; online edn, Oxford Academic, 22 Mar. 2012), https://doi.org/10.1093/acprof:oso/9780199551330.003.0014, accessed 4 Feb. 2026. </ref><ref name="Genot">Genot, E.J. The Holmesian logician: Sherlock Holmes’ “Science of Deduction and Analysis” and the logic of discovery. Synthese 198, 10169–10186 (2021). https://doi.org/10.1007/s11229-020-02709-w</ref><ref name="Uchii2010">Uchii, S. (2010). Sherlock Holmes on reasoning. Preprint. PhilSci‑Archive. Available at https://philsci-archive.pitt.edu/id/eprint/5306</ref><ref name="McCoy2021">McCoy, C. D. (2021). Meta-empirical support for eliminative reasoning. Studies in History and Philosophy of Science, 90, 15-29. https://doi.org/10.1016/j.shpsa.2021.09.002</ref>

In real-world reasoning, the fallacy arises when someone overextends this idea, treating the remaining explanation as necessarily true without having considered other plausible alternatives. It is not a formal “Holmes Method” or algorithm; it is a caution against overconfidence in elimination.<ref name="Bird2005"/><ref name="Johnson-Laird"/><ref name="Uchii2010"/><ref name="McCoy2021"/><ref name="Genot"/>

==Far-fetched hypothesis==
Holmesian fallacy and '''far-fetched hypothesis''' are closely related logical errors that involve arriving at incorrect conclusions by either mismanaging alternatives or ignoring simpler explanations. Specifically, the Holmesian fallacy involves faulty elimination of alternatives, while reliance on far-fetched hypotheses reflects a tendency to prefer unnecessarily complex or implausible explanations over simpler ones. Although distinct, they often reinforce each other in reasoning that overlooks simpler or more plausible explanations.<ref name="Hanzal2024"/><ref>Feuer, L. S. (1957). The Principle of Simplicity. Philosophy of Science, 24(2), 109–122. http://www.jstor.org/stable/185716</ref>

This peculiar fallacy tends to occur in contexts such as '''paranormal claims''' (accepting ghosts or aliens over ordinary causes), '''scientific reasoning''' (e.g., Kelvin underestimating the Sun’s age), and '''everyday thinking''' (favoring improbable explanations without considering alternatives).<ref name="Johnson-Laird"/><ref name="Genot"/>

===Illustrative Examples===
====Hypothetical crop circle scenario====
It is typically offered by [[ghost]] enthusiasts as an example of why one must not discount belief in the [[spirit]] world.<ref>[http://itcvoices.org/sir-arthur-conan-doyles-improbable-truth/ Sir Arthur Conan Doyle’s Improbable Truth] Ghost Box Communication</ref><ref>[https://www.legendsofamerica.com/gh-seeghosts/ Seeing ghosts] Legendsofamerica.com</ref><ref>[http://www.paranormalsocieties.com/view_society.cfm?id=4129 Jackson Purchase Paranormal Investigations]</ref> [[Star Trek]]'s Spock even uttered a version of it in ''Star Trek VI — The Undiscovered Country''.<ref>[https://www.youtube.com/watch?v=3B34XVV3DWQ Starteck IV Spock Logic I] YouTube</ref> It's no surprise that [[paranormal]] claims of all kinds have adopted this fallacy. For example, [[crop circles]]:
{{quotebox|Look at that [[Cattle mutilation|mutilated cow]] in the field, and see that flattened grass. Since the farmer is away and couldn't have done the deed, [[aliens]] must have landed in a [[flying saucer]] and savaged the cow to learn more about the beings on our planet.}}

Naturally, these are not the only explanations. Angry neighbors, rival farmers, pranksters, predators (not the [[Arnold Schwarzenegger|Schwarzenegger]] movie kind), undetonated ordnance from a past [[war]] (if applicable), and many other perfectly mundane probabilities exist that must be eliminated. Even assuming they are, there are myriads of other [[supernatural]] or [[paranormal]] phenomena that could potentially explain the death of the cow and the flattening of the grass that would similarly need to be falsified before the conclusion of "UFOs" or "aliens" can be accepted under this logic (For example, perhaps it was attacked by an [[avian]] [[cryptid]]. Perhaps it was struck down by [Insert Deity Here]. Perhaps it was possessed by ghosts or [[demons]], causing the cow to burst as they departed its body. Perhaps it is evidence of an airborne biological weapons test by [[Monsanto]], designed to kill all cattle and force America to eat [[GMO]]-fed meat. And so on. ''Ad infinitum''.).

====Thales of Miletus====
According to [[Aristotle]] in ''De Anima'', the philosopher Thales of Miletus once said (paraphrased):
{{quotebox|The lodestone has a [[soul]] because it moves iron. This proves that all things are full of [[gods]].<ref>http://www.iep.utm.edu/thales/</ref>}}
Thales failed to falsify ''all'' alternate explanations because he didn't know that [[magnetism]] existed. Similarly, we may be disproven by future discoveries.

====Lord Kelvin and the Sun====
{{w|Lord Kelvin}} is almost infamous for these. Because he had no knowledge of nuclear fusion, isotopic decay, or nuclear fission, there was in his mind no way to reconcile the evidence that had been found by [[biologist]]s and [[geologist]]s that the [[Earth]] is at least hundreds of millions of years old with the seeming impossibility of the [[Sun]] shining almost as bright as it does today for that period. As such, he believed the Sun was at most a few million years old and that either the biologists and geologists were wrong or the Earth far predated the Sun.<ref>James, F. A. J. L. (1982). Thermodynamics and Sources of Solar Heat, 1846–1862. The British Journal for the History of Science, 15(2), 155–181. doi:10.1017/S0007087400019154</ref>

==Unfalsifiable explanations==
A common risk when overapplying elimination reasoning is that the remaining explanation may be [[Unfalsifiability|difficult or impossible to test or falsify]]. For example, someone might conclude that a phenomenon was caused by a [[supernatural]] entity, a deity or other unknown forces simply because they cannot currently identify a natural explanation.

The Holmesian fallacy does not mandate that the explanation be supernatural or mystical; it only occurs when people treat the remaining explanation as necessarily true, even though other plausible explanations may exist but have not been considered.

Historically, this type of reasoning can lead to errors. For instance, [[Arthur Conan Doyle]] (the author of Sherlock Holmes stories) personally came to believe in [[spiritualism]] and [[Cottingley fairies|fairies]]. While not literally using Holmes's quote as an algorithm, he may have been influenced by a mindset that overvalued elimination of familiar alternatives and assumed extraordinary explanations. In scientific contexts, drawing absolute conclusions without accounting for unknown variables can similarly lead to incorrect or unfalsifiable claims.

The key point is that the fallacy is about overconfidence in elimination, not about the content of the final explanation. Even improbable or unfalsifiable explanations can be mistakenly accepted if someone misapplies this reasoning.

==Legitimate use==
A more reliable approach than seeking absolute certainty is provisional inference:
# Consider multiple plausible explanations.
# Eliminate alternatives based on available evidence.
# Recognize that the remaining explanation is the best known, but not necessarily the absolute truth, since unknown factors may exist.

This mirrors how the Sherlock Holmes likely reasoned in practice (or didn't as he never actually existed): he focused on common and plausible alternatives rather than attempting to establish certainty.

It is reasonable to grant ''provisional assent'' (scientific, not logical) to an explanation if it accounts for the facts better - or more simply - than all known alternatives. This is not an "absolute" truth, merely the most probable one.

A formulation closer to what the imaginary Holmes actually practiced - rather than preached - is; "When you have eliminated the common possibilities, one of what remains must be true, no matter how improbable it may seem."

Dirk Gently, in Douglas Adams' ''The Long Dark Tea-Time of the Soul'', rejects the Holmes principle on the basis that "the impossible often has a kind of integrity to it which the merely improbable lacks." Often, impossible ideas merely suppose that there is something we don't know about, "and God knows there are enough of those". This ties in to the omniscience idea, that you should not assume that all possible explanations have been accounted for just because you personally can't think of any others.<ref>Douglas Adams, ''The Long Dark Tea-Time of the Soul'' (1988) pgs 150-51 in the 2012 Pan Books edition</ref>

==In popular culture==
The TV series {{wpl|House (TV series)|''House''}} reprises the Holmesian structure but in a modern medical setting, replacing detectives with diagnosticians. The diagnosticians try to solve unlikely medical cases by whittling down [[jargon]]-laden possible diagnoses (the differential diagnosis) into an improbable last-minute treatment. Although differential diagnosis is part of [[evidence-based medicine]], the implementation in ''House'' is not particularly realistic (especially, burglary-based evidence gathering and occasional lack of [[informed consent]]).<ref>[https://pmc.ncbi.nlm.nih.gov/articles/PMC11303220/ TV medical dramas: assessing the portrayal of public health in primetime] by Daniela Zago et al. (2024) ''Front Public Health'' 12:1432528. doi:10.3389/fpubh.2024.1432528.</ref> Differential diagnosis in [[traditional Chinese medicine]] to diagnose diseases associated with the fictional {{wpl|Zangfu|''zangfu''}} (pairs of [[meridians]]).<ref>''Zang Fu Syndromes: Differential Diagnosis and Treatment'' by John McDonald & Joel Penner (1994) Lone Wolf Press. ISBN 0965052907.</ref><ref>''The Guidelines for Differential Diagnosis in Traditional Chinese Medicine'' by Henry C. Lu (2013) CreateSpace. ISBN 1492309966.</ref>

==See also==
*[[Argument from incredulity]]
*[[Appeal to omniscience]]
*[[Slothful induction]]
*[[Explanatory Filter]]

==External links==
*[http://www.skeptical-science.com/critical-thinking/logic-sherlock-holmes/ Beware The Logic of Sherlock Holmes], Skeptical Science
*[http://theness.com/roguesgallery/index.php/logicphilosophy/a-sherlock-holmes-logical-fallacy/ A Sherlock Holmes Logical Fallacy], Steven Novella
*[http://www.frankston.com/public/?name=HolmesianFallacy The Holmesian Fallacy], Bob Frankston
*[https://talonsphilosophy.wordpress.com/2012/10/06/a-fallacy-of-sherlock-holmes/ A Fallacy of Sherlock Holmes], Philosophy 12
*[https://web.archive.org/web/20070203224052/http://www.cuyamaca.net/bruce.thompson/Fallacies/arcane.asp Arcane Explanation], Bruce Thompson
*[http://www.iep.utm.edu/fallacy/#Far-FetchedHypothesis Far-Fetched Hypothesis], Internet Encyclopedia of Philosophy
*[http://www.topherc.net/blogs/metaskepticism/2011/06/skeptical-fallacies-the-holmes-retroduction/ Skeptical Fallacies: The Holmes Retroduction], Topher Cooper

==Notes==
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==References==
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[[Category:Arguments from ignorance]]

Categories: Arguments from ignorance