Scientists are understandably irritated when philosophers announce that, beyond the stark fact that it receives special attention, contemporary science has no special claim to attention. This chapter describes some of the damage by returning to the understanding of science described in Karl Popper's masterpiece The Logic of Scientific Discovery. Where the relativist who diminishes science and the justificationist who magnifies it are prone to agree is in supposing that scepticism and relativism come to much the same thing: that to deny that science is justified is to deny that it can tell the truth. It is easy to see why the confusion of scepticism with relativism, or of justification with truth, is rationally so debilitating. Critical rationalists, who embrace both realism and scepticism, comprise an even smaller minority. Scepticism in its simplest form denies only that we ever know, in the sense of know-for-certain, whether a statement that we make is absolutely true or false.