Pseudoscience

Pseudoscience is any idea or theory that is held by its proponents to be scientific, but which is rejected by the general scientific community as fraudulent. Accordingly, the term is a pejorative one and its application to a particular theory may be viewed as controversial. The list of theories considered pseudoscience depends on which ideas have been promoted as science, and which ideas are accepted by scientific consensus. Some ideas (like phrenology in human biology) were once respected in scientific fields, but are now dismissed as pseudoscience. Others (like plate tectonics in earth science) were once scorned as pseudoscience, but are now so accepted as to be considered basic tenets within their disciplines. There are a few, such as psychoanalysis, about which there is a serious dispute as to whether they may properly be considered pseudoscience.

The term pseudoscience, which combines the Greek root pseudo, meaning false, and the Latin scientia, meaning knowledge, appears to have been used first in 1843 by Magendie, who referred to phrenology as "a pseudo-science of the present day" [1] Among its early uses was in 1844 in the Northern Journal of Medicine, I 387: "That opposite kind of innovation which pronounces what has been recognized as a branch of science, to have been a pseudo-science, composed merely of so-called facts, connected together by misapprehensions under the disguise of principles".

Phrenology is a classic example of pseudoscience.

Introduction

Some fields that are considered pseudoscience are uniformly rejected by scientists, but are not uniformly advocated as being scientific by proponents. Astrology is one such example. Casting horoscopes based on the appearance of the night sky has been used to predict the future and to analyze current events for at least two thousand years, long before the establishment of the scientific method. Although many contemporary astrologers continue in a mystical tradition that has nothing to do with science, some argue that their complicated methods are actually scientific, a view that opens the practice of astrology to the charge of "pseudoscience!" by scientists.

Generally, pseudoscientific claims either (1) lack any supportive evidence, or (2) are based on evidence that is not established by scientific methods or (3) cite well-established evidence but do not use that evidence to logically prove the conclusions asserted in the claim. Science (especially the "hard sciences" like physics and the "exact sciences" of mathematics and logic), is cloaked in a heavy prestige in most segments of modern industrialized societies. (Often, to call something "scientific" is to imply that it is true.) Desire for this prestige prompts claims that a particular practice or belief is "scientifically proven". Many professional scientists accept such notions as well, and as the gatekeepers of science, enjoy and jealously guard their role as the arbiters of truth. Theories and claims that do not follow the methods of science as they understand them are therefore to be dismissed--not only as "unscientific" or "pseudoscientific", but as fallacious.

For those whose sincerely-held theories and claims are dismissed as "pseudoscience," that label often cuts to the quick. The charge of pseudoscience can be used to imply poor training, inadequate education, faulty judgment, or outright fraud on the part of the proponents of the idea being denigrated by scientists, and thereby prompts defensive outrage among those advocates who understand the principles of science. Among non-scientists who nevertheless attribute truth and power to the sciences, the rejection of their claims as "unscientific" can provoke a different defensive reaction, a concern that their practices are being called invalid as opposed to simply unproven by scientific methods. This reaction is not uncommon in religious groups or practitioners of complementary or alternative medicine.

This article presents a number of examples of what are considered, by some (and obviously not by their defenders), as pseudoscience. It then presents a timeline of pseudoscience. Next, it situates the topic of pseudoscience as a topic in the philosophical subdiscipline called philosophy of science. As it is most often used, the term "pseudoscience" presumes a certain understanding of "science," which, while perhaps supported by most mainstream scientists, may also be vulnerable to counter-criticism. A discussion of those counter-criticisms is also presented.

Paradigmatic Examples

Numerous theories, claims, and practices have been attacked as pseudoscientific. Many continue to be so regarded. But some—including the theory of evolution, plate tectonics, the Big Bang (a term originally chosen by Fred Hoyle to poke fun at the idea[8]) and quantum mechanics—have since won general acceptance. In retrospect, the delay was clearly a result of the challenges that they posed to the accepted doctrines of the time, and of the difficulty in gathering evidence for new theories. Following are some selected areas which, rightly or wrongly, are often discussed in connection with pseudoscience today.

Astrology

Astrology, (not to be confused with the science of astronomy) refers to a species of 'fortune-telling' based on the position (relative to earth) of the sun, moon, stars, and/or constellations. The term includes several established traditions, such as Western, Chinese, and Indian astrology. Some astrologers claim scientific status for their discipline, or some aspects of it; the activity at least makes certain assumptions which ought to be subject to scientific testing.

In principle, various astrological claims might, for all anyone knows, turn out to be true. (Certainly many genuine observations of cyclic influence of, for example, the sun or moon on human activity or emotions could be made.) The major criticism of astrology is that there is no good evidence for its most characteristic claims; and that astrology as a discipline has not incorporated any serious means of self-criticism. (In fact it often functions essentially as a religious activity, impervious to research.)

Astrological researchers often complain that they cannot receive a fair hearing in scientific circles, and find it hard to have their research published in scientific journals owing to the prejudice toward their topic. They claim that their scientific critics have wrongly dismissed studies which do support astrology. An example would be Michel Gauquelin's purported discovery of correlations between some planetary positions and certain human traits such as vocations.

ESP

The category of extra-sensory perception, or ESP, encompasses claims of telepathy, telekenesis, clairvoyance, astral projection, and other psychic abilities. Scientific study of ESP was organized in the late nineteenth-century by the Society for Psychical Research, and in the 1930's, by Duke University parapsychology pioneers J.B. Rhine and Louisa Rhine. Contemporary researchers include Dean Radin and Rupert Sheldrake.

Scientific critics of ESP research complain of several types of methodological flaws including fraud, reliance on anecdotes, a "file drawer" effect (in which studies not supporting ESP are left to languish), and the misuse of statistics. Proponents insist that at least some ESP reseach meets acceptable scientific standards, and suggest that some forms of ESP might resist being studied under laboratory conditions.

Complementary and Alternative Medicine

In contrast to the mainstream Western medical tradition variously known as scientific medicine, evidence-based medicine, or allopathy (all disputed terms), there are many medical traditions and theories collectively called Complementary and Alternative Medicine (CAM; cf. holistic health) whose relationship with the mainstream is, to a greater or lesser degree, strained. These include some like osteopathy, chiropractic, homeopathy, and acupuncture which have won varying types of government recognition in some countries; as well as others like aromatherapy, herbology, orthomolecular medicine and hypnotherapy which are less established (at least in the West).

The field of medicine is methodologically vexed by the fact that many of its techniques, by their very nature, do not lend themselves to systematic testing. Some are justified on the basis of empirical (largely anecdotal) evidence of their efficacy reported by the practioners. Thus for example practitioners of Traditional Chinese Medicine (TCM) insist that their practices are as valid as conventional treatments, having withstood the tests of time and experience. If certain aspects of TCM turn out to be unhelpful (at least for some patients), the same may be said of Western medicine. And if the theoretical underpinnings of some CAMs, (like acupuncture, which involves a kind of energy called qi) seem widely divergent from Western scientific understandings, this too is permissible as science is always in flux; and in any case, doctors must prefer practical utility over theoretical consistency.

Many regard the diversity of medical traditions as roughly analogous to religious or cultural diversity--i.e. a matter of personal choice, not subject to oversight by scientific authorities from outside the tradition. Certainly religion itself has long enjoyed a close relationship with healing, as witnessed by the ubiquity of spiritual healing. Some attempts (e.g. prayer studies) have been made to evaluate the efficacy of spiritual practices for health, with mixed results.

IQ Studies

Cognitive scientists do not agree on what, if anything, intelligence is, let alone how to test for it. Nevertheless one particular measure--scores from a range of standardized Intelligence Quotient (IQ) tests--is widely used. Originally designed for educational and military use, the classic Stanford-Benet Intelligence Scale and its offshoots measure several cognitive capabilities such as language fluency, or three-dimensional thinking. While these may seem unrelated, test scores do in fact tend to correlate. The premise of IQ tests is that such capabilities all depend on some underlying factor, called the general intelligence factor. To critics, the concept smacks of metaphysics. Does "IQ" in fact measure anything at all?

Subsidiary questions relating to intelligence and IQ involve the relative importance of nature vs. nurture; and the distribution of IQ between men and women, and among the various races (cf. intelligence and race). Accusations of pseudoscience are not difficult to find in these discussions.

Psychotherapy

Freud's proposal that mental illness might be treated through talk rather than surgery, drugs, or hypnosis was only one of the startling features of psychoanalysis contrasting it to earlier conceptions of psychiatry. The concept remains controversial today. Does psychotherapy "work"? Is it any more effective than ordinary talk? (Effective at what?)

Critics additionally wonder precisely what ontological status is being claimed for various abstract entities beloved of psychological theory, such as Freud's ego and id, which would seem unavailable for scientific inspection. In what way do psychoanalysis and its successors differ from religions? The question is even more sensitive in the case of Jungian psychology and Transpersonal psychology, which are more interested in the spiritual dimension.

In The Myth of Mental Illness and other works, Thomas Szasz proposes that the entire concept of "mental illness" is a tool of social control at the hands of a "pharmacracy." In his view, a disease must be something concrete and measurable, not an abstract condition which comes into existence by vote. In this light, current attitudes toward mental illness are no more rational than nineteenth-century campaigns against onanism.

Intelligent Design

Intelligent Design, as promoted by members of the Discovery Institute, argues that the complexity and harmony of the universe and especially of life on earth, implies the existence of an intelligent creator. In answer to the objection this is essentially a religious doctrine, proponents point out that the designer need not be the Judeo-Christian God, suggesting UFO-based theories as an alternative.

To its critics, the theory was designed to circumvent U.S. prohibitions against the teaching of Creation Science as part of the scientific curricula of public schools. If so, the strategy did not work. In his decision for Kitzmiller v. Dover Area School District, Judge John E. Jones III agreed that Intelligent Design is--"a mere re-labeling of creationism, and not a scientific theory". He went on to say that

"...ID is not science. We find that ID fails on three different levels, any one of which is sufficient to preclude a determination that ID is science. They are: (1) ID violates the centuries-old ground rules of science by invoking and permitting supernatural causation; (2) the argument of irreducible complexity, central to ID, employs the same flawed and illogical contrived dualism that doomed creation science in the 1980's; and (3) ID's negative attacks on evolution have been refuted by the scientific community." (page 64)

Other

For many, at least some 'pseudoscientific' beliefs, for example that the pyramids were built not by men but by prehistoric astronauts[11], are harmless nonsense; horoscopes are read for fun by many, but taken seriously by few. Others, notably the "brights" movement, feel that such beliefs are always harmful.

According to Scott Lillenfeld, popular psychology is rife with pseudoscientific claims: self-help books, supermarket tabloids, radio call-in shows, television infomercials and 'pseudodocumentaries', the Internet, and even the nightly news promote unsupported claims about, amongst other things, extrasensory perception, psychokinesis, satanic ritual abuse, polygraph testing, subliminal persuasion, out-of-body experiences, graphology, the Rorschach Inkblot Test, facilitated communication, herbal remedies for memory enhancement, the use of hypnosis for memory recovery, and multiple personality disorder. He suggests that critically interrogating these claims is a good way of introducing students of psychology to understanding the scientific method, while also bearing in mind Stephen Jay Gould's aphorism that "exposing a falsehood necessarily affirms a truth".

The Nobel Laureate Richard Feynman recognized the importance of unconventional approaches to science, but he was bemused by the willingness of people to believe "so many wonderful things." He was however much more concerned about how ordinary people could be intimidated by experts propounding "science that isn't science", and "theories that don't work":

There are big schools of reading methods and mathematics methods, and so forth, but if you notice, you'll see the reading scores keep going down ... And I think ordinary people with commonsense ideas are intimidated by this pseudoscience. A teacher who has some good idea of how to teach her children to read is forced by the school system to do it some other way — Or a parent ... feels guilty ... because she didn't do 'the right thing', according to the experts... Richard Feynman, Cargo Cult Science

For Feynmann, it came down to a certain type of integrity, a "kind of care not to fool yourself", that was missing in what he called 'cargo cult science'.

Timeline

While skeptical criticism of superstition dates back to ancient times (e.g., the writings of Lucian), the term "pseudoscience" appears to have been used first in 1843 by Magendie, who referred to phrenology as "a pseudo-science of the present day"

1784 Louis XIV of France names a scientific committee to investigate mesmerism. Lavoisier, Benjamin Franklin, and Joseph Ignace Guillotin participate. The Committee organizes what some regard as the first placebo-controlled trial, finding Mesmer's claims baseless.

1872 Victorian polymath Francis Galton, in "A Statistical Inquiry into the Efficacy of Prayer," observes that clergymen (who presumably pray more) do not live significantly longer than men from other professions.

1885 The Society for Psychical Research (London) publishes the "Hodgson Report" declaring the Mahatma Letters of Madame Blavatsky fraudulent.

1910 The Carnegie Foundation publishes the (Abraham) Flexner Report recommending the closure of many U.S. medical schools, the survivors to be supervised by state branches of the American Medical Association. Among its targets are osteopathic, chiropractic, and naturopathic colleges.

1920's The Scientific American offers a cash-prize for successful demonstration of mediumship; illusionist Harry Houdini contributes his expertise in order to expose trickery.

1968 Charged with evaluating U.S. Air Force Project Blue Book, the (Edward) Condon Report concludes--amidst committee in-fighting and mutual accusations of bad science--that UFO's are not worth studying.

1969 Founding of two major ufology-promoting organizations: CUFOS (the J. Allen Hynek Center for UFO Studies) and MUFON (Mutual UFO Network).

1972 Stage magician James Randi "debunks" telekenetic Uri Geller, leading to mutual lawsuits.

1974 The American Association for the Advancement of Science organizes a symposium attacking the catastrophist theories of Immanuel Velikovsky. Astronomer Carl Sagan participates.

1976 Philosopher Paul Kurtz founds CSICOP, the Committee for the Scientific Investigation of Claims of the Paranormal (now known as the Committee for Skeptical Inquiry)

1976 Beginning of the antitrust case Wilk v. American Medical Association, which would ultimately find the AMA guilty of conspiracy and restraint of trade. At issue was whether the AMA had the right to forbid medical doctors from cooperating with chiropractors. The AMA lost the final appeal in 1990.

1983 San Francisco General Medical Center physician Randolf Byrd organizes a blind study of intercessory prayer, the first of many such studies. He finds the prayed-for group to be 11 % more likely to recover, a statistically-significant figure given his sample size.

1988 Ellen Bass and Laura Davis publish The Courage to Heal: A Guide for Women Survivors of Child Sexual Abuse, a book promoting Recovered Memory Therapy.

1989 Physicists Martin Fleischmann and Stanley Pons of the University of Utah announce the discovery (soon discredited) of "cold fusion."

1991 The United States government establishes an Office of Alternative Medicine (now the National Center for Complementary and Alternative Medicine) as part of the National Institutes of Health. The center supports research into CAM.

1995 Satanic ritual abuse case Hamame v. Humenasky results in a multi-million dollar verdict, the first of several against practitioners of Recovered Memory Therapy.

2005 Kitzmiller v. Dover Area School District results in a decision against Intelligent Design.

2006 20 Idaho State University faculty members sign a petition protesting their university's support for "fringe science." Their target is Bigfoot researcher, biologist D. Jeffrey Meldrum.

Pseudoscience and the Philosophy of Science

The concept of Pseudoscience is, of course, strictly related to that of science.

The distinction of science from what science is not is a fundamental problem of the philosophy of science, and is referred to as the Problem of demarcation.

There is, however, considerable disagreement not only about whether "science" can be distinguished from "pseudoscience" in any reliable and objective way, but also about whether even trying to do so is useful. The philosopher of science Paul Feyerabend argued that all attempts to distinguish science from non-science are flawed. He argued that the idea that science can or should, be run according to fixed rules is "unrealistic and pernicious... It makes our science less adaptable and more dogmatic:"  Often the term "pseudoscience" is used simply as a pejorative to express a low opinion of a given field, regardless of any objective measures; thus according to McNally, it is "little more than an inflammatory buzzword for quickly dismissing one’s opponents in media sound-bites." Similarly, Larry Laudan has suggested that 'pseudoscience' has no scientific meaning: "If we would stand up and be counted on the side of reason, we ought to drop terms like ‘pseudoscience’ and ‘unscientific’ from our vocabulary; they are just hollow phrases which do only emotive work for us".

The sociologist Marcello Truzzi distinguished between 'skeptics' and 'scoffers'. Skepticism is an essential part of science, but skepticism is properly defined as doubt, not denial. Scientists who are scoffers, according to Truzzi, fail to apply the same professional standards to their criticism of unconventional ideas that would be expected in their own fields; they appear more interested in discrediting claims of the extraordinary than in disproving them, using poor scholarship, substandard science, ad hominem attacks and rhetorical tricks rather than solid falsification. He quotes the philosopher Mario Bunge as saying: "the occasional pressure to suppress it [dissent] in the name of the orthodoxy of the day is even more injurious to science than all the forms of pseudoscience put together."

Because science is so diverse, it is hard to find any rules that will distinguish between what is scientific and what is not that can be applied consistently to all disciplines at all times. The philosopher Imre Lakatos proposed that, while it is difficult to generalise about what makes a field scientific from its methodology, it might be possible to distinguish between 'progressive' and 'degenerative' research programs, those which continue to evolve, expanding our understanding, and those which stagnate.

Thagard proposed more formally that a theory which has pretensions to be scientific can be regarded as pseudoscientific if "it has been less progressive than alternative theories over a long period of time, and faces many unsolved problems; but the community of practitioners makes little attempt to develop the theory towards solutions of the problems, shows no concern for attempts to evaluate the theory in relation to others, and is selective in considering confirmations and disconfirmations"

Kuhn saw a circularity in this, and asked 'Does a field make progress because it is a science, or is it a science because it makes progress?' He also questioned whether scientific revolutions were in fact progressive, noting that Einstein's general theory of relativity is in some ways closer to Aristotle's than either is to Newton's. Most progress in science, according to Kuhn, is not at times of scientific revolution, when one theory is replacing another, but when one paradigm is dominant, and when scientists who share common goals and understanding fill in the details by puzzle solving. He argued that, when a theory is discarded, it is not always the case (at least not at first), that the new theory is better at explaining facts. Which of two theories is 'better' is largely a subjective judgement. The reasons for discarding a theory may be that more and more anomalous findings become apparent, that reveal its weaknesses, but there is no point at which the followers of one theory abandon it in favour of a new one; instead, they cling tenaciously to the old theory, while seeking fresh explanations for the anomalies. Thus, a new theory becomes dominant not by 'converting' followers of the old theory to the new, but rather because, over time, the new view gains more and more followers until it becomes the dominant paradigm, while the older view is held in the end only by a few 'elderly hold outs'. Kuhn argued that such resistance is not unreasonable, or illogical, or wrong; instead the conservative nature of science is an essential part of what enables it to progress. At most, it might be said that the man who continues to resist the new view long after the rest of his profession has adopted a new view "has ipso facto ceased to be a scientist"

As Kuhn described them to be, the motives of the true scientist are to gain the respect and approval of his or her peers. When technical jargon is misused, or when scientific findings are represented misleadingly, to give particular claims the superficial trappings of science for some commercial or political gain, this is easily recognised as an abuse of science ; it is not an abuse that is confined to popular literature however.

Despite the complexity of the issue, solutions to the problem of demarcation have been proposed during the 20th century, that can be collected into two main lines of thinking (see also problem of demarcation, scientific method, Karl Popper and Thomas Kuhn for further discussion).

Defining science by the falsifiability of theories

The philosopher Karl Popper described science as an objective product of the human thought, as much as a nest can be seen as the objective product of a bird. Consequently, he dismissed as insignificant the philosophical tendency to concentrate on the knowledge in the subjective sense, which includes the definition of science by the behaviour of scientists as described above (see the first thesis in ).

Popper's solution of the problem of demarcation, as well as his conception of science, are extensively treated in his 1934 book "The Logic of Scientific Discovery", a book that Sir Peter Medawar, a Nobel Laureate in Physiology and Medicine, called "one of the most important documents of the twentieth century".

Popper suggested that science does not advance because we learn more and more facts. Science do not start with observations and then somehow assemble them to provide a theory, i.e., by induction; any attempt to do so would be logically unsound, because a general theory contains more information than any finite number of particular observations. Popper shows this with a simple example. Let's say we have seen millions of white swans. We are thus tempted to conclude, by the process called induction, that "All swans are white". But this derivation is logically unsound, because "millions of swans" are still fewer than "all swans", and the next swan we see might be black however many white swans we have seen. (In fact, such a theory may well have been implicitly accepted by Europeans before Australia was discovered, and black swans were found).

Rather, the advance of science consists of three steps: (1) we find a problem; (2) we try to solve the problem by a new theory; (3) we critically test our theory and, while doing this, we learn from our errors. It is in the process of critical testing of theories that Popper finds the way to distinguish science from all other things, including pseudoscience.

For Popper, there is no way a scientific theory can be proved to be true; a theory comes to be accepted because it has survived all attempts to disprove it, but it is only accepted provisionally, until something better comes along. This may be explained again with the example of swans. How could we ever prove the truth of our theory that "all swans are white"? Only by observing all swans of the universe in all past, present and future times, and showing they are all white. This is, of course, impossible. Yet, an assertion as our "all swans are white" certainly is a scientific theory (although a false one).

Following Popper, scientific theories always have the form of falsifiable universal assertions, i.e., general statements that cannot proved to be true, but can eventually found to be false when a new observation, e.g., of a black swan, disprove them. Assertions that are not falsifiable are non-scientific, and the refusal to critically discuss a theory is a non-scientific attitude as well. As Popper puts it, "those who are unwilling to expose their ideas to the hazard of refutation do not take part in the scientific game".

Accordingly, a 'pseudoscience' is a system of assertions with a superficial resemblance to science, but which is empty, in being in principle incapable of disproof. And scholars that refuse to engage in a critical discussion of their doctrine exhibit a 'pseudoscientific' attitude. Popper argued that astrology, Marxism, and Freudian psychoanalysis are all 'pseudoscientific' because they make no predictions by which their trurth can be judged, accordingly they cannot be falsified by experimental tests, and have thus no connection with the real world.

Defining science by the behavior of scientists

Popper's vision of the scientific method was itself tested by Thomas Kuhn. Kuhn concluded, from studying the history of science, that science does not progress linearly, but undergoes periodic 'revolutions', in which the nature of scientific inquiry in a field is abruptly transformed. He argued that falsification had played little part in such revolutions, and concluded that this was because rival world views are incommensurable - that it is not possible to understand one paradigm through the concepts and terminology of another.

For Kuhn, whatever we mean by scientific progress, we must account for it by examining how scientists behave, and by discovering what they value, what they tolerate, and what they disdain. What they value most, according to Kuhn, is the respect of their peers, and they achieve this by success in solving difficult 'puzzles', while working with shared rules, a shared understanding, and towards shared objectives. Kuhn maintained that typical scientists are not objective, independent thinkers, but are conservative individuals who largely accept what they have been taught. Most aim to discover what they already know - "The man who is striving to solve a problem ... knows what he wants to achieve, and he designs his instruments and directs his thoughts accordingly."

Such a closed group imposes its own expectations of rigor, and disparages claims that are, by their conventions, vague, exaggerated or untestable. Within any field of science, scientists develop a technical language that can be specific to that field, and to a lay reader, their papers may seem full of jargon, pedantry and obscurantism. No doubt what seems to be bad writing is often just bad writing, but these things also reflect an obsession with using words precisely, according to the conventions of the field. Sometimes the technical terms have strict definitions in terms of things that can be measured (operational definitions), but not always; many terms 'stand for' things not yet understood in mechanistic detail, and even in theoretical physics for instance, although most terms have some connection with observables, they are seldom of the sort that would enable them to be used as operational definitions. As Churchland observed "If a restriction in favor of operational definitions were to be followed ... most of theoretical physics would have to be dismissed as meaningless pseudoscience!" Scientists also expect any claims to be subject to peer review before publication and acceptance, and demand that any claims are accompanied by enough detail to enable them to be verified and if possible, reproduced. Some proponents of unconventional 'alternative' theories avoid this often ego-bruising process, sometimes arguing that peer review is biased in favour of conventional views, or that assertions that lie outside what is conventionally accepted cannot be evaluated fairly using methods designed for a conventional paradigm.

Popper saw dangers in the closed worlds of specialists, but while admitting that at any one moment we are 'prisoners caught in the framework of our theories', he denied that different frameworks are like mutually untranslatable languages, and argued that clashes between frameworks have stimulated some of the greatest intellectual advances. Popper accepted that he had overlooked what Kuhn called 'normal science', but for him, such 'normal' science was the activity of "the not-too critical professional, of the science student who accepts the ruling dogma of the day;... who accepts a new revolutionary theory only if almost everybody else is ready to accept it." Popper acknowledged its existence, but saw it as the product of poor teaching, and also doubted whether 'normal' science was indeed normal. Whereas Kuhn had pictured science as progressing steadily during long periods of stability within a dominant paradigm, punctuated occasionally by scientific revolutions, Popper thought that it was rare for a single paradigm to be so dominant, and that there was always a struggle between sometimes several competing theories.

Popper's analysis of science was prescriptive, he described what he thought scientists ought to do, and claimed that this is what the best scientists did. Kuhn on the other hand claimed to be describing what scientists in fact did, not what he thought they ought to do, but nevertheless he argued that it was rational to attribute the success of science to the ways that scientists behaved. Whereas Popper was scathing about the conservative scientist who accepted the dogma of the day, Kuhn proposed that this very conservatism might be important for progress to occur. He suggested that, for science to progress, it might be important that scientists agree to accept, for the moment, a certain framework, and resist attempts to question it. According to Kuhn, during normal science, scientists do not try to overthrow theories, but rather they try to bring the accepted theory into closer agreement with observed facts and other areas of knowledge and understanding. Accordingly, they tend to ignore research findings that seem to threaten the existing paradigm, and "novelty emerges only with difficulty, manifested by resistance, against a background provided by expectation."

Nevertheless, there are controversies in every area of science, and these lead to continuing change and development. In this internal debate, scientists are scornful of the selective use of experimental evidence - presenting data that seem to support claims while suppressing or dismissing data that contradict them - and peer-reviewed journals generally insist that published papers cite others in a balanced way. The philosopher Imre Lakatos attempted to accommodate this in what he called 'sophisticated falsification', arguing that it is only a succession of theories and not one given theory which can be appraised as scientific or pseudoscientific. A series of theories usually have a continuity that welds them into a research programme; the programme has a 'hard core' surrounded by a 'auxilliary hypotheses' which bear most tests, but which can be modified or replaced without threatening the core understanding.