Popper, Lakatos, Kuhn and Feyerabend occupy leading positions in Western philosophy of science in this century. To them we owe the prevailing view that scientific knowledge is never true (nor even probable), and never false (nor even improbable). Even the best scientific opinion, at any time, is nothing more than an unjustified conjecture, a socially-imposed dogma, or a fashionable gestalt. Some consequences of this attitude to scientific truth verge on the lunatic, and David Stove demonstrates how irrationalists turn the trick of concealing absurdity by a variety of logical and linguistic devices. He then examines the aetiology of the irrationalist thesis, and traces the fatal conjunction of empiricism with perfectionism back to Hume: 'Nothing fatal to empiricist philosophy of science follows from the admission that arguments from the observed to the unobserved are not the best, unless this admission is combined, as it was by Hume, with the fatal assumption that only the best will do.' In this business-like declothing of philosophical emperors, he performs a valuable service for all students of philosophy. By exposing the 'frivolous elevation of the critical attitude into a categorical imperative of intellectual life', he resurrects a philosophical basis for holding that, for example. Harvey's theory of the circulation of the blood was right. or that Ptolemaic astronomy was wrong, or that scientific knowledge has advanced over the last four hundred years. For non-philosophers and others who have always held such views, David Stove provides a lucid and amusing account of an extraordinary movement in the history of ideas.