How do we acquire knowledge, and how reliable is it? Is there a real world beyond our senses, or is each of us an isolated atom? Can we really understand the workings of society and change it for the better? In his talk at a day school on philosophy, hosted by our British comrades at Socialist Appeal, Alan Woods (editor of In Defence of Marxism) mounted a defence of materialism against the trends of subjective idealism, such as positivism and postmodernism, that deny the possibility of objective and scientific knowledge about the world and society.