Evidence of absence

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Evidence of absence is evidence of any kind that suggests something is missing or that it does not exist. What counts as evidence of absence has been a subject of debate between scientists and philosophers. It is often distinguished from absence of evidence.


An exhaustive inspection of the attic for vermin can provide evidence of absence, but any sign of mice will always suffice to the contrary.

Evidence of absence and absence of evidence are similar but distinct concepts. This distinction is captured in the aphorism "Absence of evidence is not evidence of absence." This antimetabole is often attributed to Martin Rees or Carl Sagan, but a version appeared as early as 1888 in a writing by William Wright.[1] In Sagan's words, the expression is a critique of the "impatience with ambiguity" exhibited by appeals to ignorance.[2] Despite what the expression may seem to imply, a lack of evidence can be informative. For example, when testing a new drug, if no harmful effects are observed then this suggests that the drug is safe.[3] This is because, if the drug were harmful, evidence of that fact can be expected to turn up during testing. The expectation of evidence makes its absence significant.[4]

As the previous example shows, the difference between evidence that something is absent (e.g., an observation that suggests there were no dragons here today) and simple absence of evidence (e.g., no careful research has been done) can be nuanced. Indeed, scientists will often debate whether an experiment's result should be considered evidence of absence, or if it remains absence of evidence. The debate regards whether the experiment would have detected the phenomenon of interest if it were there.[5]

The argument from ignorance for "absence of evidence" is not necessarily fallacious, for example, that a potentially life-saving new drug poses no long-term health risk unless proved otherwise. On the other hand, were such an argument to rely imprudently on the lack of research to promote its conclusion, it would be considered an informal fallacy whereas the former can be a persuasive way to shift the burden of proof in an argument or debate.[6]


In carefully designed scientific experiments, null results can be interpreted as evidence of absence.[7] Whether the scientific community will accept a null result as evidence of absence depends on many factors, including the detection power of the applied methods, the confidence of the inference, as well as confirmation bias within the community. For instance in amnesia studies, the absence of behavior indicative of memory is sometimes interpreted as the absence of the memory trace; however, certain researchers consider this interpretation flawed as the memory impairment may be temporary due to deficits in recall.[8] Alternatively, the memory trace be latent and demonstrable via its indirect effects on new learning.[9][10] Michael Davis, researcher at Emory University, argues that complete erasure can only be confidently inferred if all of the biological events that occurred when the memory was formed revert to their original status.[11] Davis contends that because making these measurements in a complex organism is implausible, the concept of complete memory erasure (what he deems "strong form of forgetting") is not useful scientifically.[11]


In many legal systems, a lack of evidence for a defendant's guilt is sufficient for acquittal. This is because of the presumption of innocence and the belief that it is worse to convict an innocent person than to let a guilty one go free.[3]

On the other hand, the absence of evidence in the defendant's favor (e.g. an alibi) can make their guilt seem more likely. A jury can be persuaded to convict because of "evidentiary lacunae", or a lack of evidence they expect to hear.[12]

Proving a negative[edit]

A negative claim is a colloquialism for an affirmative claim that asserts the non-existence or exclusion of something.[13] Proofs of negative claims are common in mathematics. Such claims include Euclid's theorem that there is no largest prime number, and Arrow's impossibility theorem. There can be multiple claims within a debate, nevertheless, whoever makes a claim usually carries the burden of proof regardless of positive or negative content in the claim.[14] [15]

A negative claim may or may not exist as a counterpoint to a previous claim. A proof of impossibility or an evidence of absence argument are typical methods to fulfill the burden of proof for a negative claim.[13][16]

Philosopher Steven Hales argues that typically one can logically be as confident with the negation of an affirmation. Hales says that if one's standards of certainty leads them to say "there is never 'proof' of non-existence", then they must also say that "there is never 'proof' of existence either". Hales argues that there are many cases where we may be able to prove something does not exist with as much certainty as proving something does exist.[13]: 109–112  A similar position is taken by philosopher Stephen Law who highlights that rather than focusing on the existence of "proof", a better question would be whether there is any reasonable doubt for existence or non-existence.[17]

See also[edit]


  1. ^ "Absence of Evidence Is Not Evidence of Absence". Quote Investigator. 2019-09-17. Retrieved 2021-10-23.
  2. ^ Sagan, Carl (1997). The Demon-Haunted World: Science as a Candle in the Dark (1st ed.). New York: Ballantine. p. 213. ISBN 0-345-40946-9. OCLC 32855551. Appeal to ignorance—the claim that whatever has not been proved false must be true, and vice versa (e.g., There is no compelling evidence that UFOs are not visiting the Earth; therefore UFOs exist—and there is intelligent life elsewhere in the Universe. Or: There may be seventy kazillion other worlds, but not one is known to have the moral advancement of the Earth, so we're still central to the Universe.) This impatience with ambiguity can be criticized in the phrase: absence of evidence is not evidence of absence.
  3. ^ a b Copi, Irving; Cohen, Carl; McMahon, Kenneth (2014). Introduction to Logic (14 ed.). Harlow, UK: Pearson Education Limited. pp. 132–133. ISBN 978-1-292-02482-0.
  4. ^ Martin, M. (2007). The Cambridge Companion to Atheism. Cambridge Companions to Philosophy. Cambridge University Press. p. 70. ISBN 9780521842709. LCCN 2006005949. [Advocates] of the presumption of atheism... insist that it is precisely the absence of evidence for theism that justifies their claim that God does not exist. The problem with such a position is captured neatly by the aphorism, beloved of forensic scientists, that "absence of evidence is not evidence of absence." The absence of evidence is evidence of absence only in case in which, were the postulated entity to exist, we should expect to have more evidence of its existence than we do.
  5. ^ Schreuder, Duco A. (2014). Vision and Visual Perception The Conscious Base of Seeing. p. 105.
  6. ^ Walton, Douglas (1992). "Nonfallacious Arguments from Ignorance". American Philosophical Quarterly. 29 (4): 381–387. ISSN 0003-0481. JSTOR 20014433.
  7. ^ Altman, Douglas G; Bland, J Martin (1995). "Absence of evidence is not evidence of absence". British Medical Journal. 311 (19 August): 485. doi:10.1136/bmj.311.7003.485. PMC 2550545. PMID 7647644.
  8. ^ Roediger, Henry L.; Dudai, Yadin; Fitzpatrick, Susan M., eds. (2007). Science of memory: concepts. Science of memory. London: Oxford Univ. Press. p. 186. ISBN 978-0-19-531044-3. Does the amnestic agent block consolidation, or now reconsolidation, or impair retrieval? Is the memory deficit permanent or is there spontaneous recovery or the possibility of recovering the memory by further treatments or reminders? It is evident that the same logical objection voiced by Weiskrantz (1966)...He warned that experimental amnesia studies are fatally flawed from the outset, since it is not possible to prove the null hypothesis, i.e. the absence of a memory trace.
  9. ^ Eichenbaum, Howard. "Persistence: Necessary but not Sufficient." Science of memory: Concepts (2007): 193-197.
  10. ^ Wixted, J. T. "Integrative comments. Forgetting: It's not just the opposite of remembering (2007) Science of memory concepts." 329-335. "However, it would be difficult to establish the complete absence of a trace because it is always possible that an as yet untried retrieval cue would show that some remnant of the trace is still available."
  11. ^ a b Davis, Michael. "Forgetting: Once again, it’s all about representations." Science of memory: Concepts (2007): 317-320.
  12. ^ Tuzet, Giovanni (2015), Bustamante, Thomas; Dahlman, Christian (eds.), "On the Absence of Evidence", Argument Types and Fallacies in Legal Argumentation, Law and Philosophy Library, Cham: Springer International Publishing, vol. 112, pp. 37–51, doi:10.1007/978-3-319-16148-8_3, ISBN 978-3-319-16148-8, retrieved 2021-10-21
  13. ^ a b c Hales, Steven D. (Summer 2005). "Thinking tools: You can prove a negative" (PDF). Think. Cambridge University Press. 4 (10): 109–112. doi:10.1017/S1477175600001287. S2CID 170305277.
  14. ^ Quine, William Van Orman (1978). The Web of Belief. Random House. p. 8. ISBN 978-0394321790.
  15. ^ Truzzi, Marcello (August 1987). "Zetetic Ruminations on Skepticism and Anomalies in Science". Zetetic Scholar (12 & 13): 3–4. Retrieved 5 July 2023.
  16. ^ Damer, T. Edward (2009). Attacking faulty reasoning: a practical guide to fallacy-free arguments. Cengage Learning. p. 17. ISBN 9780495095064.
  17. ^ "You Can Prove a Negative | Psychology Today". www.psychologytoday.com. Retrieved 2022-11-28.