Book: The Logic of Scientific Discovery

Overview
Karl Popper's The Logic of Scientific Discovery (1934) reshaped the philosophy of science by proposing a clear test for what counts as scientific knowledge. Popper rejects verification by repeated observation as the hallmark of science and replaces it with the demand that scientific theories be falsifiable: a genuinely scientific theory must rule out possible observations and therefore be open to refutation. The book frames scientific progress as a rational, critical activity driven by bold conjectures subjected to severe tests.

Falsifiability and the Demarcation Problem
Falsifiability becomes the central criterion for distinguishing scientific theories from metaphysical or pseudoscientific claims. A theory that cannot, even in principle, be shown false by observation is not scientific because it lacks empirical content. Popper emphasizes that scientific status depends on the logical form of claims: universal generalizations make risky predictions and so expose themselves to potential refutation, whereas tautologies or ad hoc adjustments avoid risk and escape scientific scrutiny.

Critique of Induction
Popper offers a sustained critique of inductivism, arguing that no finite set of observations can logically justify a universal law. Observational agreement can support confidence but cannot provide deductive proof or probabilistic justification sufficient to transform a hypothesis into a confirmed law. The so-called problem of induction is thereby dissolved by replacing induction with a normative methodology: propose hypotheses conjecturally and attempt to refute them empirically.

Deductive Testing and Corroboration
Hypotheses are tested through the deduction of observational consequences; a failed prediction falsifies the hypothesis, while surviving tests increase its empirical corroboration. Popper stresses an asymmetry: while a single counterinstance can logically falsify a universal claim, no finite accumulation of positive instances can conclusively verify it. Corroboration is therefore not confirmation of truth but a record of a hypothesis having withstood rigorous attempts at refutation and thereby earning provisional standing.

Ad Hoc Adjustments and the Role of Risk
Ad hoc modifications that save a theory from falsification without increasing its empirical content are methodologically illegitimate. Genuine theoretical progress favors theories that make bold, risky predictions because such theories expose themselves to potential refutation and, if they survive, provide stronger tests. The notion of empirical content is crucial: more informative theories rule out more possible states of affairs and are thus more testable.

Probability, Truthlikeness, and Objective Knowledge
Popper challenges traditional interpretations of probability and inductive confirmation, arguing that logical probability cannot restore inductive justification. He introduces the idea of verisimilitude or "truthlikeness" to capture how scientific theories can become closer to the truth despite never being conclusively verified. Knowledge grows objectively through a cycle of conjectures and refutations, with error elimination as the driving force rather than accumulation of positive instances.

Methodological and Historical Impact
The Logic of Scientific Discovery influenced both philosophy and scientific practice by foregrounding critical scrutiny and skepticism toward claims of final justification. Popper's critical rationalism inspired debates about theory choice, the structure of scientific revolutions, and the sociology of scientific knowledge. While disputed on several technical points, such as the treatment of auxiliary hypotheses and the formalization of corroboration, the work endures as a seminal challenge to verificationism and a foundational statement about the epistemic role of falsifiability.