Chapter 1: The Demarcation Problem

Logical Positivism: The Verification Principle

The Vienna Circle (discussed in detail in Chapter 4) proposed the verification principleas a demarcation criterion: a statement is meaningful if and only if it is either analytically true (true by definition) or empirically verifiable. Statements that are neither — including the pronouncements of metaphysics, theology, and ethics — are not false but literally meaningless.

The verification principle faced devastating objections. It appeared to be self-refuting: the principle itself is neither analytic nor empirically verifiable, so by its own criterion it is meaningless. Successive reformulations (weak verification, confirmability in principle) only multiplied the problems. By the 1950s, even sympathizers acknowledged that the verification principle could not serve as a criterion of demarcation. This failure set the stage for Popper’s alternative.

Karl Popper (1902–1994) proposed what remains the most influential solution to the demarcation problem. In The Logic of Scientific Discovery (1934/1959) and Conjectures and Refutations(1963), Popper argued that the distinguishing feature of science is not that its theories are verifiable, but that they are falsifiable.

A theory is scientific if and only if it makes predictions that could, in principle, be shown to be false by observation or experiment. The key logical insight is an asymmetry between verification and falsification: no finite number of observations can verify a universal statement (“All swans are white”), but a single observation can falsify it (one black swan). Science advances not by confirming theories but by subjecting them to severe tests and eliminating those that fail.

“It must be possible for an empirical scientific system to be refuted by experience... I shall not require of a scientific system that it shall be capable of being singled out, once and for all, in a positive sense; but I shall require that its logical form shall be such that it can be singled out, by means of empirical tests, in a negative sense: it must be possible for an empirical scientific system to be refuted by experience.”— Karl Popper, The Logic of Scientific Discovery (1934), §6

Popper’s motivating examples were drawn from early 20th-century intellectual life in Vienna. He was struck by the contrast between Einstein’s general theory of relativity — which made the bold, risky prediction that light would be deflected by gravity (confirmed by Eddington’s 1919 eclipse observations) — and the theories of Marx, Freud, and Adler, which seemed compatible with any possible observation.

Freudian psychoanalysis, Popper argued, could explain any behavior: a man who pushes a child into water to drown and a man who sacrifices his life to save the child could both be “explained” by the theory (the first by repression, the second by sublimation). A theory that is compatible with everything explains nothing. It is precisely the riskiness of a scientific theory — its willingness to “stick its neck out” — that distinguishes it from pseudoscience.

Criticisms of Falsifiability

Popper’s criterion, while enormously influential, has been subjected to powerful objections:

• •The Duhem-Quine problem: No scientific hypothesis faces the tribunal of experience alone. Every test involves auxiliary assumptions (about instruments, background conditions, etc.). When a prediction fails, it is always logically possible to blame an auxiliary assumption rather than the core theory. This means no theory is strictly falsifiable in isolation (see Chapter 6).
• •Too broad: Some paradigmatically non-scientific claims are falsifiable. “All marriages between Sagittarians and Leos end in divorce” is falsifiable but is clearly astrology, not science.
• •Too narrow: Some paradigmatically scientific claims are not straightforwardly falsifiable. Existential statements like “There exist black holes” cannot be falsified by any finite number of failed observations. Probabilistic theories (e.g., in quantum mechanics) do not make categorical predictions.
• •Historical inaccuracy: Kuhn showed that scientists do not, in practice, abandon theories at the first sign of falsification. Anomalies are common and are typically shelved rather than treated as refutations.

Thomas Kuhn (1922–1996) offered a radically different account. In The Structure of Scientific Revolutions (1962), Kuhn argued that the distinctive feature of mature science is not falsifiability but the presence of a paradigm — a shared framework of theories, methods, standards, and exemplary problem-solutions (exemplars) that defines a scientific community.

For Kuhn, what distinguishes science from non-science is not any logical feature of its theories but a sociological one: mature sciences engage in puzzle-solvingwithin the framework of an accepted paradigm. Just as a crossword puzzle has a definite solution and rules for finding it, scientific problems have solutions constrained by paradigmatic assumptions. A scientist who fails to solve a puzzle has failed as a scientist, not refuted the paradigm.

“One of the things a scientific community acquires with a paradigm is a criterion for choosing problems that, while the paradigm is taken for granted, can be assumed to have solutions. To a great extent these are the only problems that the community will admit as scientific or encourage its members to undertake.”— Thomas Kuhn, The Structure of Scientific Revolutions (1962), p. 37

On Kuhn’s view, astrology fails to be a science not because it is unfalsifiable (it makes many falsifiable predictions) but because it never developed a tradition of puzzle-solving. When astrological predictions fail, there is no mechanism for identifying and correcting errors within the framework. Compare this with astronomy, where discrepancies between prediction and observation generate productive research programmes.

Kuhn’s criterion has its own difficulties. It seems to make demarcation a sociological rather than an epistemological matter. It is also unclear how to apply it to immature sciences (those that have not yet achieved paradigm status) or to interdisciplinary fields. Nonetheless, Kuhn’s insight that science is a communal activity governed by shared standards has profoundly shaped subsequent discussion.

Imre Lakatos (1922–1974) attempted to synthesize the insights of Popper and Kuhn. His methodology of scientific research programmes distinguishes between the hard core of a theory (which is treated as irrefutable by methodological decision), a protective belt of auxiliary hypotheses (which can be modified to absorb anomalies), a negative heuristic (which directs researchers away from modifying the hard core), and a positive heuristic (which guides the development of the protective belt).

For Lakatos, the demarcation criterion is progressiveness. A research programme is scientifically progressive if it occasionally predicts novel facts — facts not used in the construction of the theory. A programme is degenerating if it only accommodates facts after the fact, through ad hoc modifications. Science is characterized by progressive research programmes; pseudoscience by degenerating ones.

“A research programme is said to be progressing as long as its theoretical growth anticipates its empirical growth, that is, as long as it keeps predicting novel facts with some success... it is stagnating if its theoretical growth lags behind its empirical growth, that is, as long as it gives only post-hoc explanations either of chance discoveries or of facts anticipated by, and discovered in, a rival programme.”— Imre Lakatos, “Falsification and the Methodology of Scientific Research Programmes” (1970)

Lakatos’s approach has the virtue of being more historically accurate than Popper’s: it acknowledges that scientists rightly hold on to theories in the face of anomalies, as long as the programme continues to be progressive. However, critics (especially Feyerabend) argued that the distinction between progressive and degenerating programmes can only be made in retrospect, and that programmes often appear to degenerate before making a dramatic comeback.

In a landmark 1983 paper, Larry Laudan argued that the demarcation problem is a pseudo-problem. Every proposed criterion, he contended, either fails to exclude clear cases of pseudoscience or excludes clear cases of science. There is no set of necessary and sufficient conditions that captures the extension of “science.”

Laudan proposed that we abandon the science/non-science distinction in favor of a more fine-grained assessment of the epistemic credentials of individual claims and methods. Rather than asking “Is this scientific?” we should ask “Is this well-supported by evidence?” “Is the methodology reliable?” “Are the inferences valid?” The label “science” is, on Laudan’s view, a honorific that obscures rather than illuminates.

“If we would stand up and be counted on the side of reason, we ought to drop terms like ‘pseudo-science’ and ‘unscientific’ from our vocabulary; they are just hollow phrases which do only emotive work for us.”— Larry Laudan, “The Demise of the Demarcation Problem” (1983)

Laudan’s skepticism has been influential but not universally accepted. Many philosophers (including Paul Thagard, Massimo Pigliucci, and Sven Ove Hansson) have argued that the failure to find a simple criterion does not mean that demarcation is impossible. It may require a multi-criteria approach rather than a single litmus test.

Paul Thagard proposed that pseudoscience should be identified not by a single feature but by a constellation of characteristics. On his account, a theory or discipline is pseudoscientific if and only if:

1. It has been less progressive than alternative theories over a long period of time
2. The community of practitioners makes little attempt to develop the theory toward solutions of the problems
3. The community shows no concern for attempts to evaluate the theory in relation to others
4. The community is selective in considering confirmations and disconfirmations

Thagard’s approach is explicitly comparative: a theory is pseudoscientific relative to a more progressive alternative. This handles cases like astrology (which is pseudoscientific relative to astronomy) without requiring a single sharp criterion. However, it has difficulty with cases where there is no clear alternative (as some have argued about string theory).

The demarcation problem has been litigated in US courts, most famously in cases involving the teaching of creationism in public schools. These cases have forced judges to articulate criteria for what counts as “science.”

Where does the demarcation problem stand today? Several positions are defended in the contemporary literature:

• •Multi-criteria approaches (Pigliucci, Hansson, Mahner): Science is characterized by a cluster of features — testability, progressiveness, theoretical integration, methodological rigor, community standards — none of which is individually necessary or sufficient.
• •Family resemblance (Dupre, Irzik & Nola): “Science” is a Wittgensteinian family-resemblance concept. There is no essence of science, but there are overlapping similarities that connect the various sciences.
• •Social epistemological approaches (Longino): Science is demarcated not by the content of its theories but by the social processes through which they are produced — including critical scrutiny, shared standards, uptake of criticism, and equality of intellectual authority.
• •Pragmatic approaches: The demarcation problem need not be solved in the abstract. Different contexts (courts, funding agencies, classrooms) may appropriately use different criteria.

“The demarcation between science and pseudoscience is not merely a problem of armchair philosophy: it is of vital social and political importance.”— Massimo Pigliucci, Nonsense on Stilts (2010)