Philosophy of Science: Popper, Kuhn, Lakatos

The Demarcation Problem

What distinguishes science from non-science? Karl Popper, in "The Logic of Scientific Discovery" (1934), proposed the criterion of falsifiability: a theory is scientific if it is in principle refutable—if there exist (even hypothetical) observations that could disprove it.

Einsteinian physics: if starlight does not deflect near the Sun—the theory is false. This observation can be made—and was made (Eddington, 1919). Freud's theory of the unconscious: any behavior can be explained through psychoanalysis. There is no observation that could disprove it. This is not science, but "pseudoscience" in Popper's sense—regardless of its practical value.

Popper proposed an asymmetry: a theory cannot be confirmed by a million examples—one counterexample refutes it. Science advances not through verification but through falsification: the creation of bold hypotheses and attempts to disprove them. Theories survive if no refutation has yet been found.

Thomas Kuhn: Normal Science and Revolutions

Thomas Kuhn, in "The Structure of Scientific Revolutions" (1962), challenged Popper's image of science as continuous falsificationism. The actual history of science looks different.

Normal science: most of the time, scientists work within a paradigm—a set of shared assumptions, methods, and exemplars for solving problems. The paradigm determines what questions to ask, what methods to use, what counts as a solution. Within normal science, scientists "solve puzzles," without questioning the paradigm itself.

Anomalies and Crisis: observations accumulate that don't fit the paradigm. At first, they are ignored or explained ad hoc. When anomalies become too numerous—a crisis occurs.

Revolution: the crisis is resolved by a change of paradigm—a "gestalt switch" after which the world appears differently. Supporters of different paradigms speak different languages and perceive the same experience differently. Paradigms are incommensurable—there is no neutral ground for their comparison.

Kuhn was radical: a change of paradigm is not a rational choice of the better theory, but a social process associated with a change of generations. Scientists don't "convert" under the pressure of data—they die, and a new generation adopts the new paradigm.

Lakatos: Research Programs

Imre Lakatos proposed a compromise between Popper and Kuhn. Science consists of research programs—systems of theories with a "hard core" (protected from falsification) and a "protective belt" of auxiliary hypotheses (which are modified when confronted with anomalies).

A program is progressive if its modifications predict new facts (confirmed by observation). A program degenerates if its modifications only explain known anomalies ad hoc, without making new predictions.

This allows for the preservation of programs in the face of anomalies (as Kuhn claimed) while simultaneously providing a criterion for rational appraisal (as Popper demanded). The Newtonian program was progressive: it predicted Neptune (1846). Ptolemy's program by the 16th century had degenerated into a sea of epicycles.