Falsifiability Is the Demarcation Criterion of Science

Popper believed the hallmark of a scientific theory is not that it can be verified but that it can be falsified. "It might rain tomorrow" is a scientific statement (testable by observation); "all things have spirit" is not (cannot be refuted by any observation). Falsifiability gives scientific theories information content — they exclude certain possibilities.

Source: The Logic of Scientific Discovery (Logik der Forschung), Karl Popper, 1934/1959 (Hutchinson)

Knowledge Grows Through a Cycle of Conjectures and Refutations

Popper "critical rationalism" holds that scientific progress does not occur through induction (from observation to theory) but through deduction (propose conjecture → attempt to falsify → conjecture survives or is refuted → propose better conjecture). We can never prove a theory true, but we can prove it false — scientific knowledge is provisional and revisable.

Source: Conjectures and Refutations, Karl Popper, 1963 (Routledge)

Open Society: Critical Discussion Is the Foundation of Freedom

Popper believed the "open society" is one that allows critical discussion and can reform institutions peacefully, in contrast to the "closed society" (authority based on myth, tradition, or historical necessity). His core political conviction: no theory or leader can claim to possess ultimate historical truth; institutions must allow for error correction.

Source: The Open Society and Its Enemies, Karl Popper, 1945 (Routledge)

Historicism Is Wrong: History Has No Inevitable Laws

In The Poverty of Historicism, Popper criticized "historicism" — the belief that history follows predictable laws (such as Marx class struggle laws, Hegel dialectics). He argued history is open and unpredictable; the illusion of "historical laws" leads to totalitarianism — using "historical necessity" to justify violence.

Source: The Poverty of Historicism, Karl Popper, 1957 (Routledge)

Falsifiability Test

Ask: what evidence could refute this theory?

Freudian psychoanalysis vs. Einstein relativity: Freudian theory can explain any behavior (no matter how a patient behaves, a psychoanalytic explanation can be found), so it cannot be falsified; Einstein general relativity predicted that light would bend in a gravitational field — a specific prediction falsifiable by astronomical observation, confirmed by the 1919 solar eclipse observation.

Conjecture-Refutation Cycle

Bold conjectures, rigorous refutations, retain surviving theories

Discovery of antibiotics: Fleming "penicillin can kill bacteria" was a bold conjecture; subsequent laboratory tests were refutation attempts; the conjecture survived and was refined, ultimately becoming the foundation of modern antibiotic theory.

Piecemeal Social Engineering (vs Utopian Engineering)

Small-step, error-correctable reforms rather than large-scale utopian reconstruction

Marxist revolution vs. Nordic social democratic reform: Marxist utopian engineering (reconstructing society all at once according to historical laws) led to violence and authoritarianism multiple times in the 20th century; Nordic piecemeal reform (gradually expanding social security, correctable policy experiments) achieved high welfare without destroying liberal institutions.

Critical Rationalism: Criticism Instead of Authority

Any authority can be criticized; no theory is beyond questioning

Soros reflexivity theory: George Soros, as Popper student, applied critical rationalism to investing — his "reflexivity" theory holds that market participants cognition affects the market itself, so any theory about markets must include a self-correction mechanism.

Vienna Phase: Formation of Falsificationism (1919-1934)

1919-1934

Vienna Circle Influence and Independent Criticism

Popper received his education in Vienna, with close contact with the Vienna Circle (logical positivism), but he criticized the logical positivists verification principle (meaningful statements must be verifiable), proposing falsificationism as an alternative. Published the German Logik der Forschung (later translated as The Logic of Scientific Discovery) in 1934.

New Zealand Phase: Political Philosophy Transformation (1937-1945)

1937-1945

Rise of Fascism and Formation of Open Society Theory

Popper left Europe under the Nazi threat, teaching at Canterbury University in New Zealand. During WWII, he applied falsificationism methodology to political philosophy, writing The Open Society and Its Enemies (1945) and The Poverty of Historicism (1944-45), criticizing the collectivism and historicism of Plato, Hegel, and Marx.

LSE Phase: Intellectual Maturity and International Influence (1946-1994)

1946-1994

Deepening Philosophy of Science and Spreading Political Liberalism

Popper taught at the London School of Economics until 1969, training a generation of scholars including George Soros. Published important works including Conjectures and Refutations (1963) and Objective Knowledge (1972). His 1965 debate with Kuhn in London became a landmark event in the history of philosophy of science. Died in 1994 at age 92.