The fundamental philosophical contribution of Austrian-born Karl Popper (1902-1994) is his falsification theory of knowledge. Sometimes it is contrasted with the ‘verificationism’ that emerged from the Vienna Circle in the inter-war period, arrestingly introduced to the English-reading public in A.J. Ayer’s youthful tour de force, Language, Truth, and Logic (1936). But the two enterprises are really quite different. Verificationism seeks to create criteria for meaning, suggesting that the meaning of a proposition can be derived from the way in which it is verified and that, therefore, propositions that were neither true by definition (‘all unmarried men are bachelors’) nor verifiable by observation (‘there is a cat on the mat’) were meaningless. When I was a philosophy undergraduate, in the atheistic environment of 1980s Oxford, ‘God is Love’ was held up as a paradigm case of a proposition which, being neither self-evident from its terms nor provable by empirical means, was not merely wrong but meaningless.
