On the Extraordinary: An Attempt at Clarification
Marcello Truzzi
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In one page
Marcello Truzzi founded Zetetic Scholar to give proponents and critics of unusual claims a shared arena, and he opened its first issue by setting the evidence bar the site's ladder inherits: the burden of proof sits with the claimant, and it rises in proportion to how extraordinary the claim is. The article that follows does the harder job of defining the word. Extraordinary, Truzzi argues, means theoretically unexpected — unexpected against the body of scientific knowledge of the day, not merely rare or startling to the public — so it is relative to a frame of reference and it is a continuum rather than a switch. He then separates three things that debates routinely fuse: the event, which runs from ordinary to extraordinary; the witness, who runs from credible to non-credible; and the narrative, which runs from plausible to implausible. Laid on a grid of ordinary and extraordinary events against ordinary and extraordinary explanations, this yields a working order of inquiry, and a closing rule the whole ladder rests on: unproved is not disproved.
Why it matters hereChapter 1 builds its evidence ladder on the principle that the weight of evidence demanded should scale with how much a claim would overturn. This is where that principle was written down, by the person who wrote it — and it supplies the precision the slogan loses, that extraordinariness is measured against theoretical expectation, comes in degrees, and belongs to the event rather than to the person reporting it.
What it claims
01The burden of proof in science rests on the claimant, and where the claims are extraordinary the burden of proof increases proportionately — so a skeptical starting position toward an extraordinary claim is ordinary scientific practice. Truzzi immediately adds the limit: skepticism should not be confused with dogmatic denial.Editorial, page 2
Settled physics02Extraordinary must mean theoretically unexpected, measured against the general body of scientific knowledge at the time, rather than merely rare or surprising to a lay observer. A 30-inch adult is abnormal, not paranormal; a beast the theory says is extinct is extraordinary to the scientist and ordinary to the people who see it every day.Section ‘The Extraordinary as Relative and Measurable’, pages 15 to 16
Settled physics03Extraordinariness is a continuum expressing degrees of expectation and surprise, not a dichotomy — and the degree matters directly, because it sets how much and what quality of evidence a scientist should require before accepting a claim.Section ‘The Extraordinary as Relative and Measurable’, pages 15 to 16
Settled physics04Three things that get fused in argument should be graded separately: the event, on a scale from ordinary to extraordinary; the witness or narrator, on a scale from credible to non-credible; and the narrative itself, on a scale from plausible to implausible. Calling an event ‘incredible’ is a category error — credibility belongs to the witness.Section ‘Dimensions of the Reasonable’, pages 16 to 17
Settled physics05Sorting claims on a grid of ordinary and extraordinary events against ordinary and extraordinary explanations gives an order of inquiry: first ask whether the event happened at all, then look for an ordinary explanation of an established extraordinary event, avoid extraordinary explanations of ordinary events on grounds of parsimony, and only then consider an extraordinary explanation — and consider all of the competing extraordinary explanations, because falsifying one does not validate another.Section ‘Extraordinary Events versus Extraordinary Explanations’, pages 12 to 14
Settled physics06Where a plausible report of an extraordinary event exists but the evidence is thin, the correct position is that the evidence is inconclusive: one may give such a report low priority, but to say something is unproved is not the same as saying it is disproved, and the standard of further evidence required must be proportional to the theoretical extraordinariness of the claim.Closing pages, page 18 to 19
Settled physics
The way in
https://archive.org/details/Zetetic_Scholar_No_01SOURCE READ IN FULL. The complete first issue of Zetetic Scholar is scanned and openly readable at the Internet Archive, and the article and the editorial were both read there on 2026-09-11; the page images carry the line ‘Copyright 1978 by Marcello Truzzi’, so this sheet carries a summary and short quotations rather than the text. WHICH SENTENCE IS WHERE. The wording the evidence bar is usually credited with — that an extraordinary claim needs proof of matching weight — is Truzzi’s, but in this issue it is put in the editorial on page 2: ‘the burden of proof in science must be upon the claimant. And where the claims are extraordinary, the burden of proof increases proportionately.’ The article on pages 11 to 19 is the longer piece that says what ‘extraordinary’ has to mean for that rule to be usable. Both are by Truzzi and both are in this one issue.
How to cite it
Marcello Truzzi (1978) On the Extraordinary: An Attempt at Clarification. https://archive.org/details/Zetetic_Scholar_No_01
Where it sits in the curriculum