You might ask why we should care what an Austrian philosopher of science who has been dead for 18 years thought about the nature of scientific inquiry. Yet much of what Karl Popper contributed to the philosophy of science has now passed into mainstream thought, into the currency of that nebulous, tricky ontology known as "common sense". In the case of philosophers such as Popper, their work is, in a sense, too recent to be able to evaluate with the level of hindsight that we might apply to more distant thinkers, such as David Hume, and yet it is worth attempting to unpack.
Born in 1902, in Vienna, the young Popper demonstrated a broad range of interests (music was a dominant passion) and an inquiring mind: he entered into the intellectual hotbed of Austrian culture, attending lectures by Einstein, investigating the psychotherapeutic theories of Freud and Adler, and becoming a Marxist. He decided at the age of 17 that the latter ideology was unsustainable, in large part as a result of an incident during his brief time in the Austrian Communist party, in which eight of Popper's friends were shot by the police in a riot instigated by the party in 1919. When Popper, somewhat naturally, complained to party leaders about this, he was told that loss of life was inevitable in the runup to revolution: Popper disagreed, and this sparked his lifelong commitment to political moderation, tolerance and liberalism.
The search for truth was, Popper considered, the strongest motivation for scientific discovery. His role was to determine how we can ascribe truth to the claims made by science, religion and politics. He did not, however, become a member of the Vienna Circle, that group of intellectuals who, following on from the work of Wittgenstein (the Tractatus mark-one version of that philosopher) aimed at the unification of the sciences and the wholesale rejection of metaphysics. Popper's antipathy to Wittgenstein meant that he was not invited to become a member of this particular group, but being cast in the role of the formal opposition seems to have honed his own thinking on logical positivism. Following on from Hume and the latter's rejection of induction, Popper took a stand against an empiricist view of science, endeavouring to show via his rejection of verificationism, and consequent espousal of falsificationism, how scientific theories progress. The fundamental principle of falsificationism is this: any contradictory instance to a theory is sufficient to falsify that theory, regardless of how many positive examples appear to support it.
Attempts to present theories such as Marxism, Adlerian psychology and astrology as scientific are subjected by Popper to his own analysis of falsificationism, and fail the test. It is perhaps worth noting that Popper's own doctorate was in psychology, attained in 1928.
Popper's work, therefore, was fuelled by a number of engines: a disillusionment with Marxism, the increase of Austrian fascism, which led to his move to New Zealand in 1937 and then London in 1946, and a distaste for the psychological models of the day. Popper's concerns over attempts to present psychology as a science, in contrast to the approach demonstrated by physicists such as Einstein, provide the groundwork to his work on falsifiability. Einstein's physics, which Popper regarded as somewhat unstable, nonetheless contains the parameters for its own falsifiability: we can say what it would take to render the theory false.
This, Popper pointed out, was not the same for psychological theories, which are unfalsifiable in principia. The bulk of Popper's work in this particular area was done in the 1930s, in The Logic of Scientific Discovery.
During his time in New Zealand, Popper wrote his principal political tract, The Open Society and Its Enemies, a two-volume work in which both Plato and Marx come under fire. He criticised historicist analyses, in which society proceeds according to fixed and predictable political laws, and claimed that such analyses formed the basis for both ancient and modern totalitarianism. Epistemology is directly linked to politics within Popper's work: certainty forms the basis for totalitarian thought, and yet it is a certainty that is baseless if considered scientifically.
Popper died in 1994, having influenced the course of the philosophy of science throughout the 20th century. He remains one of the most significant commentators within the discipline, and the effects of his work are still being felt today both within and beyond the philosophy of science, connecting as they do epistemology, politics, and the scientific method.