Nowadays, "positivist" is a term of abuse; for, if we follow Habermas, a positivist is a man who claims, in a pseudo-scientific manner, that he has a monopoly of scientific knowledge, and who has a blinkered conception of science. It seems to be a commonplace that positivism is dead — so why on earth should we bother with it? Nevertheless, to do so has a twofold justification: Even if the situation is as disastrous as it seems to be, it is important to know what went wrong on the road from Humean scepticism to modern Logical Positivism; for Hume's call to abolish theology and school metaphysics as sophistry and illusion and to commit them to the flames, is precisely analogous to contemporary criticism of dogmas and ideologies as pseudo-sciences. How, then, is it possible for an approach which set out to unmask ideology, to be accused of being a pseudo-science itself? Our question is primarily a systematic rather than a historical one, for if we succeed in showing at what point the positivist programme became unworkable, we may hope to learn how to develop alternatives which might be more successful.