Popper’s method of demarcation consists essentially of the single criterion of falsifiability (although some authors have wanted to combine it with the additional criteria that tests are actually performed and their outcomes respected, see Section 4.2). Most of the other criteria discussed above are similarly mono-criterial, of course with Merton’s proposal as a major exception.
Karl Popper described the demarcation problem as the “key to most of the fundamental problems in the philosophy of science” (Popper 1962, 42). He rejected verifiability as a criterion for a scientific theory or hypothesis to be scientific, rather than pseudoscientific or metaphysical. Instead he proposed as a criterion that the theory be falsifiable, or more precisely that “statements or systems of statements, in order to be ranked as scientific, must be capable of conflicting with possible, or conceivable observations” (Popper 1962, 39).
From a practical point of view, the distinction is important for decision guidance in both private and public life. Since science is our most reliable source of knowledge in a wide range of areas, we need to distinguish scientific knowledge from its look-alikes. Due to the high status of science in present-day society, attempts to exaggerate the scientific status of various claims, teachings, and products are common enough to make the demarcation issue pressing in many areas. The demarcation issue is therefore important in practical applications such as the following:
The demarcation between science and pseudoscience is part of the larger task of determining which beliefs are epistemically warranted. This entry clarifies the specific nature of pseudoscience in relation to other categories of non-scientific doctrines and practices, including science denial (ism) and resistance to the facts.
Thomas Kuhn is one of many philosophers for whom Popper’s view on the demarcation problem was a starting-point for developing their own ideas. Kuhn criticized Popper for characterizing “the entire scientific enterprise in terms that apply only to its occasional revolutionary parts” (Kuhn 1974, 802). Popper’s focus on falsifications of theories led to a concentration on the rather rare instances when a whole theory is at stake. According to Kuhn, the way in which science works on such occasions cannot be used to characterize the entire scientific enterprise. Instead it is in “normal science”, the science that takes place between the unusual moments of scientific revolutions, that we find the characteristics by which science can be distinguished from other activities (Kuhn 1974, 801).
Hence, Grove (1985, 219) included among the pseudoscientific doctrines those that “purport to offer alternative accounts to those of science or claim to explain what science cannot explain.” Similarly, Lugg (1987, 227–228) maintained that “the clairvoyant’s predictions are pseudoscientific whether or not they are correct”, despite the fact that most clairvoyants do not profess to be practitioners of science. In this sense, pseudoscience is assumed to include not only doctrines contrary to science proclaimed to be scientific but doctrines contrary to science tout court, whether or not they are put forward in the name of science. Arguably, the crucial issue is not whether something is called “science” but whether it is claimed to have the function of science, namely to provide the most reliable information about its subject-matter. To cover this wider sense of pseudoscience, (2′) can be modified as follows (Hansson 1996, 2013):
Some authors have maintained that the demarcation between science and pseudoscience must be timeless. If this were true , then it would be contradictory to label something as pseudoscience at one but not another point in time. Hence, after showing that creationism is in some respects similar to some doctrines from the early 18th century, one author maintained that “if such an activity was describable as science then, there is a cause for describing it as science now” (Dolby 1987, 207). This argument is based on a fundamental misconception of science. It is an essential feature of science that it methodically strives for improvement through empirical testing, intellectual criticism, and the exploration of new terrain. A standpoint or theory cannot be scientific unless it relates adequately to this process of improvement, which means as a minimum that well-founded rejections of previous scientific standpoints are accepted. The practical demarcation of science cannot be timeless, for the simple reason that science itself is not timeless.