The aim of this text is to analyze the issue of relativism. The author argues that the relativist position can be interpreted in two ways. According to the first interpretation, relativism denies the possibility of objectivity. According to the second interpretation, relativism denies the existence of anthropological universals, and a fortiori the idea of human nature. This text focus only on the first version of the relativistic position. From an epistemological point of view, the author identifies two arguments that have been proposed to justify relativism, and he shows that both are controversial. From an explanatory point of view, he shows that the relativistic thesis is incapable to account for real life behavior of scientists, who are keen to evaluate the truth of their theories against data and against rival theories.