“Absence of evidence is not evidence of absence.”
I first encountered this phrase during one of the worst professional stretches of my life. My research proposal had just been rejected — again — and a mentor slid a sticky note across the desk toward me without saying a word. Written in her cramped, hurried handwriting were those eight words. I stared at them for a long moment, honestly a little annoyed. It felt like a fortune cookie, something you’d find printed on a motivational poster in a dentist’s waiting room. Then she said, quietly, “The committee didn’t find your evidence. That doesn’t mean your evidence doesn’t exist.” Something shifted. I carried that sticky note in my jacket pocket for three months, and every time I pulled it out, it meant something slightly different. That’s the mark of a genuinely durable idea — it keeps finding you at exactly the right moment. So where did this deceptively simple maxim actually come from? The answer is far more interesting — and far older — than most people realize.
The Quote in Blockquote Form > “Absence of evidence is not evidence of absence.” This compact logical principle carries enormous intellectual weight. Additionally, it applies across disciplines — from archaeology to astronomy, from biology to criminal law. However, most people who quote it today casually attribute it to Carl Sagan or Martin Rees. As we’ll explore, the real story stretches back much further than either of those celebrated scientists. — The Earliest Known Roots: William Wright and the Hittites (1887) The trail leads back to a Victorian-era theologian and scholar named Reverend William Wright. In January 1887, Wright delivered a paper to the Victoria Institute — a philosophical society in Great Britain — arguing for the historical reality of Hittite settlements in southern Palestine. Critics at the time argued that, because Egyptian inscriptions rarely mentioned Hittites in the southern regions, those settlements probably never existed. Wright pushed back forcefully. His argument was elegant in its simplicity: the Egyptians wrote about places they actually visited. Therefore, their silence about Hittites in Hebron proved nothing, because Egyptian armies never marched to Hebron. His exact words deserve attention: > “It is urged that the Hittites could not have been settled in Southern Palestine because there are few direct references to their southern settlements in the inscriptions. To this I reply, that the absence of evidence is not evidence.” Notice something important here. Wright’s phrasing was truncated — he wrote “absence of evidence is not evidence,” not the full modern formulation. Nevertheless, the logical core was already fully formed. He understood that the absence of a record reflects the limits of the recorder, not necessarily the limits of reality. This distinction — between what we know and what is — sits at the heart of epistemology. Additionally, it would echo through scientific and historical writing for the next century and beyond. — The Livestock Dispute That Sharpened the Logic (1891) Four years later, an unlikely arena sharpened the phrase further: a heated dispute about a bull.
In October 1891, London’s Live Stock Journal published a letter from a man named William Housman. Housman was arguing about whether a bull named Lancaster Comet had actually left a particular farm during a specific three-year period. His opponent, a Mr. Fowler, claimed the missing records proved the bull had relocated. Housman’s response was sharp and precise: > “May I point out to Mr. Fowler the distinction between absence of evidence and evidence of absence?” This formulation is notably more sophisticated than Wright’s. Housman explicitly named both sides of the logical distinction. Furthermore, he framed it as a formal logical error — not just a rhetorical point. In doing so, he brought the concept closer to the crisp, memorable maxim we recognize today. The mundane subject matter — cattle records — makes the philosophical precision even more striking. Good logic, it turns out, doesn’t require grand subjects. — Geologists Enter the Debate (1895) By 1895, the phrase had migrated into the natural sciences. W. J. Sollas, a Professor of Geology at the University of Dublin, used the concept directly in an article published by The Quarterly Journal of the Geological Society of London. Sollas was challenging scientists who dismissed the idea that glaciers could lift stones from their floors into their bodies. His critics, he argued, were making a classic logical error — treating the absence of observed examples as proof that the phenomenon was impossible. Meanwhile, new fieldwork in Greenland was already revealing exactly the mechanism his critics had denied. His argument demonstrated something crucial: this wasn’t just a rhetorical flourish. It was a genuine scientific principle with real consequences for how researchers interpret negative results. The First Exact Match: Dugald Bell (1895) Later that same year, in December 1895, The Glacialists’ Magazine published an article by Thomas Sheppard on Scandinavian boulders found in England. Sheppard credited another scientist for the phrase: > “It has been remarked by Mr. Dugald Bell that ‘absence of evidence is not evidence of absence.’” This is, as far as current research can determine, the earliest known instance of the exact modern phrasing. Dugald Bell — not Sagan, not Rees — appears to have coined or at least popularized the precise formulation we still use today. However, Bell remains an obscure figure, and Sheppard’s attribution suggests the phrase was already circulating in scientific circles before it appeared in print.
— The Phrase Spreads Across Disciplines (1939–1953) For several decades after 1895, the maxim quietly circulated in specialist publications. Then, in 1939, The Yorkshire Post used it in an article about prehistoric Viking boat burials. The author pointed out that wooden boats rot — so their absence from the archaeological record tells us nothing definitive about whether they existed. By 1947, the phrase had reached a naturalist hunting for orchids in Connecticut. The naturalist recalled it as a “warning” — suggesting it had already achieved the status of a well-known cautionary principle, something passed between scientists like practical wisdom. In 1953, The Honolulu Advertiser invoked it in a discussion about whether the giant moa bird of New Zealand might still be alive. The logic was compelling: millions of acres of unexplored wilderness in New Zealand’s South Island meant that the absence of confirmed sightings couldn’t definitively prove extinction. Additionally, this application to wildlife and extinction debates shows how broadly the principle had traveled by mid-century. — NASA, Martin Rees, and the Extraterrestrial Connection (1971–1972) The phrase took a quantum leap in visibility when NASA entered the picture. In 1971, a summer research program sponsored by NASA and Stanford University tackled one of the biggest questions imaginable: how might humanity detect intelligent extraterrestrial life? The resulting technical report, known as Project Cyclops, used the phrase as the epigraph for its second chapter — and attributed it to cosmologist Martin Rees. This attribution gave the maxim enormous institutional credibility. Furthermore, it placed the phrase squarely within the SETI (Search for Extraterrestrial Intelligence) conversation, where it has remained ever since. In December 1972, astronomer Richard Berendzen invoked it at a symposium on the possibility of life on other worlds. His point was straightforward: the fact that we had found no evidence of life elsewhere didn’t mean life elsewhere didn’t exist. It simply meant our instruments and methods hadn’t yet found it. Therefore, the search should continue.
— Carl Sagan Brings It to the Mainstream (1977) Five years later, Carl Sagan — perhaps the most gifted science communicator of the twentieth century — used the phrase in his 1977 book The Dragons of Eden. Sagan applied it to neuroscience, arguing that the failure to localize all higher brain functions didn’t mean those functions couldn’t eventually be mapped. Sagan’s reach was extraordinary. His books sold millions of copies. His television series Cosmos reached hundreds of millions of viewers worldwide. As a result, when Sagan used a phrase, it stuck. Many people who encountered “absence of evidence is not evidence of absence” through Sagan assumed he had invented it. In reality, he was passing on wisdom that had already traveled through archaeology, livestock disputes, geology, naturalism, and space science over the course of nearly a century. This is not a criticism of Sagan. He was a brilliant synthesizer and communicator. However, accurate attribution matters — both for intellectual honesty and for understanding how ideas actually evolve. — Why the Misattribution Happened Misattribution is extremely common with short, memorable phrases. The mechanism is simple: a famous person uses a phrase in a widely read work, and readers assume origination rather than transmission. Additionally, the internet accelerated this process dramatically. A single viral post attributing the quote to Sagan or Rees can reach millions of people before any correction circulates. Martin Rees, for his part, likely encountered the phrase through scientific channels before the 1971 NASA report. However, neither Rees nor Sagan appears to have claimed original authorship. The attribution to them arose organically — through the natural human tendency to anchor memorable ideas to memorable people. Meanwhile, Dugald Bell — the man most likely responsible for the exact modern phrasing — remains almost entirely unknown. His name appears in a single footnote in a Victorian geology magazine. This is, in its own way, a perfect illustration of how intellectual history actually works: the person who coins a phrase rarely receives lasting credit, while the person who amplifies it becomes synonymous with it. — The Logic Behind the Phrase It’s worth pausing to appreciate why this principle matters so much across so many fields. The phrase captures a fundamental asymmetry in logic. Specifically, it distinguishes between two very different epistemic states: 1. We searched and found nothing. 2. We searched and found proof that nothing exists. These two states are not equivalent. The first reflects the limits of our search. The second would require exhaustive, perfect knowledge — something almost never achievable in science or history. Additionally, the principle guards against a specific cognitive bias: the tendency to treat our current knowledge as complete. Humans naturally assume that if something important existed, we would already know about it. This assumption has been wrong repeatedly throughout history — from the discovery of bacteria to the detection of gravitational waves to the ongoing revision of human evolutionary timelines. — Modern Usage and Cultural Impact Today, the phrase appears in courtrooms, laboratories, philosophy classrooms, and online debates about everything from UFOs to the existence of God. Defense attorneys use it to challenge prosecutors who rely on missing evidence. Scientists use it to argue for continued research funding. Theologians use it in arguments about the nature of divine existence. In popular culture, the phrase has become a kind of intellectual shorthand — a way of signaling that one understands the difference between not knowing and knowing the negative. Furthermore, it appears regularly in discussions about artificial intelligence, where the absence of observed machine consciousness is sometimes incorrectly cited as proof that machine consciousness is impossible. The phrase also carries genuine emotional resonance. When someone tells you that your hypothesis is wrong because you haven’t proven it yet, this maxim offers a precise, dignified response. It doesn’t claim certainty. Instead, it demands intellectual humility — from both sides of the argument. — A Timeline Summary To organize the history clearly: – 1887: Reverend William Source Wright uses a truncated version — “absence of evidence is not evidence” — in a paper about Hittite settlements. Source – 1891: William Housman explicitly contrasts “absence of evidence” with “evidence of absence” in a livestock journal. – 1895: W. J. Sollas applies the concept to glaciology. Dugald Bell, credited by Thomas Sheppard, produces the first known exact match of the modern phrase. – 1939–1953: The phrase spreads through journalism, natural history, and archaeology. – 1971: NASA’s Project Cyclops uses it as a chapter epigraph, attributing it to Martin Rees. – 1972: Astronomer Richard Berendzen deploys it at a major scientific symposium. – 1977: Carl Sagan uses it in The Dragons of Eden, cementing it in popular scientific consciousness. — What This History Teaches Us The journey of this phrase is itself a lesson in the principle it expresses. For decades, researchers assumed the quote originated with Sagan or Rees — simply because earlier evidence hadn’t surfaced yet. The absence of documented earlier sources wasn’t evidence that earlier sources didn’t exist. They did. They were just waiting to be found. Additionally, the phrase’s multi-disciplinary evolution reveals something important about how useful ideas spread. They don’t travel in straight lines from a single genius. Instead, they percolate through different fields, get refined by different thinkers, and eventually crystallize into a form that sticks. Dugald Bell may have coined the exact phrase, but William Wright, William Housman, and W. J. Sollas all contributed to shaping the intellectual context that made the phrase necessary. In summary, “absence of evidence is not evidence of absence” is not just a clever saying. It’s a compressed epistemological argument — one that has protected scientific inquiry, sharpened historical reasoning, and challenged lazy conclusions for well over a century. The next time someone dismisses a hypothesis because the proof hasn’t arrived yet, you’ll know exactly what to say. And now you’ll also know that the person who first said it clearly was probably a Victorian geologist named Dugald Bell — not Carl Sagan, not Martin Rees, and definitely not the internet. The evidence was always there. We just hadn’t looked hard enough.