The assumptions underlying this contribution are, first, that educational research, like research in other fields, is expected to yield knowledge. This is rather uncontroversial. It is only when it comes to the definition of knowledge, the kinds of knowledge sought and to questions as to whose knowledge counts, that the debate characteristically becomes more heated. Second, and perhaps more controversially, a discussion of the nature and purposes of educational research will, at some stage, have to engage with the notion of truth. Despite having traditionally been a serious philosophical subject, the idea of truth has in recent times become rather unpopular, an "idea non grata." The reconceptualisation of knowledge and the decline of truth are due in no small part to the increased popularity of certain kinds of postcolonial theory, postmodernism, constructivism and feminist thought, the rise of subaltern science and alternative epistemologies in academia. This article critically examines current trends in the theory of educational research: the case against 'crypto-positivism' and 'hyperrationality', and the trend in favour of 'epistemological diversity' and 'critical constructivist epistemology', especially against the backdrop of the decline of truth as a significant subject and yardstick that is currently exercising and restraining us, as educational researchers, philosophers and as persons.