What are some historical examples of theories/ideas that were initially labeled "pseudoscience" and later considered legitimate "science"? I don't mean theories or ideas that were initially not accepted or ignored and later accepted, but things that were derided as pseudoscientific (and labeled as such) but then either evidence or new theories eventually made them considered "science." Something akin to the hypothetical where "dowsing" was suddenly given a mechanistic and experimental basis that convinced the scientific community to accept it as "real science" (or similarly for parapsychic powers).

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    $\begingroup$ I seem to recall that plate tectonics was once considered pseudoscience and is now accepted as established science. $\endgroup$
    – nwr
    Commented Aug 28, 2018 at 16:42
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    $\begingroup$ Is there a time range for this? Distinctions between pseudoscience and science are a 20th century creation, so the question is not very sound historically. There was no sharp separation between alchemy and chemistry or astrology and astronomy before mid 18th century, for example, see Secrets of Nature: Astrology and Alchemy in Early Modern Europe volume. $\endgroup$
    – Conifold
    Commented Aug 28, 2018 at 19:25
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    $\begingroup$ This isn't a valid question because "pseudoscience" is a nonword, like "fake news" or "alternative medicine." Now, if you want examples of valid research which took a long time to be accepted, consider plate tectonics, ulcers and rotavirus, or even cleanliness and reduced maternal childbirth death. $\endgroup$ Commented Aug 29, 2018 at 11:49
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    $\begingroup$ @CarlWitthoft it's perfectly valid. I am asking for historical examples when people were accused of their work/experiments/theories being 'not science' (or called explicitly 'pseudoscience') and it later becoming accepted as science/part of consensus. If you read my question, I specifically said I am not looking for examples of theories that were not accepted (but not disputed as "not science"). (Conifold: any time range with the caveat that the label "pseudoscience" was coined at a specific point like you said) $\endgroup$
    – user7496
    Commented Aug 30, 2018 at 18:20
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    $\begingroup$ Then your question is even less reasonable. There are far too many anti-science people (and there have been far too many of them in the past) to give any value to shouts of "pseudoscience" against any nascent theory. $\endgroup$ Commented Aug 30, 2018 at 18:42

8 Answers 8


For a long while it was widely believed that the main cause of peptic ulcer disease was stress or spicy food. When the theory arose that it was in fact usually an infection this was rejected by the medical establishment. The Greek physician John Lykoudis was in fact fined for his treatment of patients with antibiotics. Subsequent work by Australian scientists identified the bacterium responsible Helicobacter pylori and they were awarded the Nobel for their work. A full timeline is available on Wikipedia. It is far too long to summarise here.

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    $\begingroup$ The most spectacular episode of that controversy was when Dr Barry Marshall intentionally swallowed a disgusting concoction of H. pylori bacteria. He promptly developed nasty stomach ulcers. Then he took antibiotics to cure them. He really earned that Nobel Prize. $\endgroup$
    – dain
    Commented Jan 7, 2023 at 13:19
  • $\begingroup$ @dain: Sounds like a case worthy of the snopes treatment... $\endgroup$ Commented Sep 4, 2023 at 19:00

*copied from my answer to another question

It seems ball lightning was disbelieved by scientists until around 1960. See Wikipedia .

I knew a geologist who told us how his eye-witness account of ball lightning had been ridiculed. He had learned not to mention it when he interviewed for jobs as a professor of geology.


Plate tectonics

It was put forth by a meterologist, and offered no explanation how, given the solid crust and mantle, the continents could drift about like icebergs on the liquid core.

The discovery of processes by which a solid surface could indeed drift about took decades, but finally triumphed.


The germ theory of disease, and in general the importance of handwashing was a fringe viewpoint for a long time. Good evidence existed since at least the early 19th century that micro-organisms could cause disease, but the medical profession was very slow on the uptake.

Dr Semmelweis, though he lacked any theoretical model, saved the lives of many mothers and newborns by his insistence on handwashing in his maternity ward. Despite strong empirical evidence, the scientific community largely hated his ideas, and the acrimony led to the poor doctor suffering a nervous breakdown and premature death.

  • $\begingroup$ This is a particularly interesting one in that apparently at various times and places, the idea that invisible organisms or "seeds" cause disease has been flirted with for a couple of thousand years. It is baffling that something like this was resisted well past the invention of microscopes and scientists who vehemently advocated for it. (Semmelweis really got the short end of the stick, but not the first or last person who paid dearly for the crime of being right.) $\endgroup$
    – releseabe
    Commented May 3 at 8:11

I have an impression that until about 1800 scientists did not believe that rocks could fall from the sky, but I don't have a better source than the following:

Reports of fireballs accompanied by the fall of iron or stony objects go back to ancient times, and some of those objects were kept and thought of as sacred. But by the 18th century, scholars remained generally dismissive of popular accounts of such events, deeming them fanciful and as expressions of superstition and ignorance. By the turn of the 19th century, with a growing number of reports on fireballs accompanied by falling stones from various parts of the world, they started to change their minds.

  • $\begingroup$ what is super interesting to me is that at least one guy, decades before nuclear energy was understood, suggested that the sun was powered by such rocks falling into it. While that sound crazy, without understanding fusion/fission, the vast output of the sun was unexplainable. $\endgroup$
    – releseabe
    Commented Sep 15, 2023 at 11:21

In mathematics, infinitesimals were widely considered not merely "pseudoscience" but "chimeras", "hallucinations", "cholera bacilli", "fantasies", "abominations", "debasement of meaning", "hazy mist", "empty words", and what not, and altogether an intellectual embarassment to shun as a plague. One of the major objections was of theological origin; see this publication.

This went on for hundreds of years until in the second half of the 20th century, serviceable theories of infinitesimals were finally developed. A vigorous debate continues until this day, including a recent lively exchange in the pages of The Mathematical Intelligencer.

Note added on 2 may 2024: A related point is that atomism was already envisioned by Democritus over 2400 years ago. Democritus' doctrine was considered a rival doctrine to Aristotle's. In the middle ages, catholic theologians interpreted Aristotle's doctrine in terms of hylomorphism and proceeded to condemn Democritus' doctrine as not merely incorrect but blasphemous and contrary to canon (specifically, canon 2 of Session 13 of the Council of Trent). Atomism we take for granted today is different from Democritus' doctrine, but nevertheless closer to it than the rival doctrine attributed to Aristotle.

Galileo's 1632 trial did not actually mention the issue of Trent 13 canon 2, but it was mentioned in a couple of anonymous denunciations leading up to the trial. One of them dates from literally a few months before the trial; its author was identified through handwriting analysis as jesuit Melchior. Orazio Grassi similarly attacked Galileo with the weapon of eucharistic theology.

As far as Aristotle is concerned, the issue is not so much what he meant or how we understand him today, but rather how he was interpreted by catholic theologians in the 17th century. Arguably, they understood hylemorphism as a physical doctrine explaining the eucharist in terms of substitution of the hyle-stratum (while retaining the external characteristics/morphism such as form, taste, smell, and color). Perhaps this can be explained in the framework of atomism, but they certainly didn't think so.

The generals of the jesuit order issued several bans on teaching atoms/indivisibles. The bans applied explicitly to both physical and mathematical indivisibles. My interest in this lies not so much in Galileo as in Cavalieri. In his case, the doctrinal issue was apparently never mentioned explicitly in print, though his critic Guldin appears to have alluded to it in his book. I have a forthcoming article on this.


The "golden" age of alchemy was about 1300–1700 CE and was replaced by more empirically based chemistry. Alchemists dreamed of finding the philosopher's stone, a material that would transform other metals into gold, but it was based in occultism and mysticism.

We had to wait until the 20th century to show that (nuclear) transmutation is actually possible via relativistic quantum mechanical effects. Some elements (like bismuth, platinum or mercury) can be now transmuted into gold either by gamma or neutron scattering experiments (experiments that are more expensive than the quantities of gold produced). Also some elements naturally decay into gold (after a very very long time).

  • $\begingroup$ @kimchilover it has been fixed $\endgroup$
    – Mauricio
    Commented May 2 at 23:59

It is somewhat astonishing that a phenomenon that was commonly thought of as belonging to the realm of parapsychology or superstition, has become an object of scientific investigation and its existence has been increasingly accepted as possible in scientific environments.

I refer to telepathy: nowadays, a sound and serious scientific research in the field is carried on, also by universities as MIT, Harvard and Washington University. These new researches suggest that some forms of telepathy are possible.

Of course, we are not speaking of telepathy as told by parapsychologists or occultism, as folding a fork with the force of the mind or voluntary communicating with another person with the force of thought, and of course not reproducible in everyday life.

But the scientific world has been increasingly aware that some forms of communication between ‘brains’ are possible.

A forerunner of neuroscience in regarding telepathy not as a superstition but an actual phenomenon, deserving attention even if not understood, can be considered psychoanalysis.

It is enough well known that telepathy is a phenomenon that has been regarded, for many years, not as paranormal or pseudo- scientific by serious communities as Freudian societies: the Freudian societies are deemed as the more ‘scientific’ and rigorous psychoanalytic communities, not at all inclined to accept fancy or imaginative phenomena.

Freud itself paid attention to telepathy and to which he called ‘unconscious communication’ mainly in two works, Psychoanalysis and Telepathy and Dream and telepathy, both written in 1921.

A controversial debate took place in those years about the matter, in particular there was a
disagreement with Ernest Jones, about the explicit ‘resistance’ of Freud and other psychoanalysts towards extrasensory phenomena. And a general tendency to ignore these phenomena followed in subsequent years .

But Freud kept alive his long-standing curiosity toward the transmission of thought and extrasensory phenomena, as witnessed for instance by several essays he devoted to dreams and occultism in the period 1921-1932. Freud states clearly that he is very skeptical about supernatural phenomena, but at the same time his attitude became more positive, particularly toward telepathy.

In psychoanalytic communities, in more recent times, has been increasingly accepted that some experiences of telepathy, not explained but frequently observed, occur in psychoanalytical clinical context, where some strange, unexpected, ‘telepathic’ phenomena manifest themselves (mainly in dreams), in which someone guesses some thought or some aspect of the life of another person, without any apparent information about them. For examples of papers about this subject see (1).

If psychoanalysis can be considered science or not is subject of discussion. But, of course, these are not scientific investigations in the sense of ‘hard sciences’ as commonly understood.

But, nowadays , the possibility of telepathy isn't any longer considered an irrational and fancy hypothesis also by ‘harder’ scientists as neuroscientists. It is viewed as a possible field of research in neurosciences about the functioning of the human brain, about which we don’t still know very much.

This is a recent news by BBC:

Scientists 'make telepathy breakthrough'

Research led by experts at Harvard University shows technology can be used to send a simple mental message from one person to another without any contact between the two. Neuroscientist Giulio Ruffini told the Today programme: "You can actually transmit information directly from one brain to another brain without intervention of the senses." "The next step would be to try to find more powerful techniques to send more complex >information," he added.


Below an article on the matter of a serious and well-known Italian review of scientific dissemination, Focus. I translate the beginning of the article of Focus,

From Focus:

Is telepathy scientifically possible?

Not exactly as in movies, but something similar to telepathy exists. And research is making progress.

In scientific terms, we speak of brain-to-brain communication, and some experiments of recent years prove that it is possible to put in connection brains of several individual through a ‘computerized neural interface’, called BCI ( brain-computer interface). This instrument registers, encodes and decodes electrical impulses, which can be transmitted by radio, wi-fi, internet and so on.


Other related links, from MIT, are:



In short, therefore, we can say that telepathy is in progress of being carried from pseudoscience to science, even if it seems, as far as I know, that research in the field is still at its beginning.

(1) For examples of books and papers about telepathy and psychoanalysis :





This last paper is by some of the most prominent and appreciated Italian psychoanalysts.

  • $\begingroup$ I want to point out that what I wrote is perfectly scientific and well known in wide intellectual and scientific communities in many countries, for a few decades, it isn't a new matter. And there are, as I show, papers on the subjet published in many important journals and universities, not at all 'antiscientific'. What is science and what is pseudo-science cannot established by me or someone else, but the only possible criterion here is the acceptance by intellectual and scientific communities, and now thelepaty is object of serious investigation, it is a fact, and a well known fact. $\endgroup$ Commented Jan 17, 2023 at 12:00
  • $\begingroup$ In this site we are talking of hystory and social hystory of science, and what I described is what happened in scientific communities. History is not a matter of opinions, or of believing or not believing to thelepathy, but history must report the actual facts of science and what happens in scientific communities, without prejudice and subjective judgments. $\endgroup$ Commented Jan 17, 2023 at 12:07
  • $\begingroup$ I'd argue very strongly that with a machine interface it isn't exactly telepathy, more that we have a way of interpreting signals via a computer and then transmitting those signals on - no different essentially to speaking and listening, reading, or watching a movie - the signal has been transformed into a medium (electronic in your case, in my case spoken word, written word etc) that can then be transmitted (heard, read, watched in my case) $\endgroup$
    – bob1
    Commented May 6 at 21:37

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