The Logic of Scientific Discovery

Popper's first published book, a treatise on how science works that he later expanded into English with many new appendices. It starts from two problems: induction, which Hume showed cannot be justified, and demarcation, the question of what separates science from non-science. Popper's answer to both is falsifiability. Scientific theories are never verified by observation, however many confirming cases pile up; they are bold conjectures that must forbid certain outcomes and can therefore be refuted by a single sound counter-instance. Science advances by proposing theories and testing them severely, not by generalising from data. The book then discusses basic statements and why their acceptance rests on decision, degrees of falsifiability, simplicity as testability, and corroboration, Popper's term for how well a theory has survived tests. Long chapters treat probability and quantum theory. Critics, including Kuhn and Lakatos, argued that scientists rarely abandon a theory after one failed prediction.

Its idea that a good theory is one that sticks its neck out remains the most widely known account of the scientific method, and the debate it began is still active.