Conjectures and Refutations: The Growth of Scientific Knowledge

The central argument is that scientific knowledge grows through a process of conjecture and refutation: scientists propose bold hypotheses, then subject them to severe criticism and attempted refutation. The book reorients epistemology away from the traditional question of justification—how do we know?—toward the question of growth: how does knowledge develop? Popper argues that the rational attitude is not the search for certainty but the willingness to expose our theories to criticism and to let them be refuted. This is what he calls the 'critical attitude,' and it is the basis of both science and the open society. The book applies this method across a range of topics: the demarcation of science from pseudo-science, the nature of metaphysical theories, the role of tradition in science, and the political implications of fallibilism.

Popper distinguishes science from pseudo-science by the criterion of falsifiability. A theory is scientific if it makes predictions that could, in principle, be refuted by observation. Pseudo-sciences, such as Freudian psychoanalysis and Adlerian psychology, fail this test because they can explain any possible observation and therefore cannot be refuted. Popper illustrates the distinction with the contrast between Einstein's theory of relativity, which made risky predictions that could have refuted it, and the theories of Freud and Adler, which seemed to explain everything. The distinction matters because it is not merely a matter of classification: it is a matter of intellectual honesty. Science is characterised by the willingness to be wrong, while pseudo-science protects itself from criticism by making its theories unfalsifiable.

The critical attitude is the willingness to expose one's beliefs to criticism, to seek out evidence that might refute them, and to revise them in the light of that evidence. It is the attitude that makes science possible. Popper argues that the same attitude is essential to the open society: a society in which individuals are free to criticise their rulers, and in which institutions are designed to allow for the correction of error. The connection between science and politics is not accidental: Popper sees the critical attitude as the common foundation of both. The dogmatic attitude, by contrast, is the enemy of both science and democracy. It is characterised by the refusal to consider criticism and the insistence on a single truth. The book thus develops the political implications of Popper's epistemology.

Conjectures and Refutations was published in 1963 and collects essays and lectures written over the preceding two decades. The essays had been published in various journals and volumes, and Popper revised them for the collection. The book is thus a composite, but it is unified by the central theme of the growth of knowledge. It is closely related to The Logic of Scientific Discovery (1934; English translation 1959), which established the falsificationist account of science, and to Objective Knowledge (1972), which develops the evolutionary epistemology that underlies it. The book also contains important essays on the history of science, including 'The Nature of Philosophical Problems and Their Roots in Science' and 'The Demarcation between Science and Metaphysics,' which show Popper engaging with the history and sociology of science.

The main criticisms are that Popper's account is too individualistic and too rationalistic. Kuhn argued that science is a collective enterprise governed by paradigms, and that scientists do not abandon theories as soon as they encounter anomalies. Lakatos argued that Popper's falsificationism is naive because it ignores the tenacity of research programmes and the role of auxiliary hypotheses. Other critics have noted that observations are theory-laden, so it is not always clear what counts as a falsifying instance. Popper's response is that these criticisms describe the sociology of science, not its logic. He acknowledges that scientists are often dogmatic, but he insists that the rationality of science lies in its willingness to expose theories to criticism, not in the mechanical application of a rule. The debate remains central to the philosophy of science.

The most common misunderstanding is that Popper is claiming that scientists should actively try to falsify their theories and abandon them at the first sign of trouble. In fact, he is making a logical and methodological point, not a psychological or sociological one. He does not deny that scientists are often attached to their theories, and he does not recommend that they give them up at the first anomaly. His point is that the rationality of science lies in the willingness to subject theories to criticism and to revise them in the light of evidence. A related misunderstanding is that Popper is dismissing metaphysics as meaningless. In fact, he argues that metaphysical theories can be meaningful and can serve as fruitful conjectures, even if they are not falsifiable. The book is a defence of the critical attitude, not a crusade against metaphysics.