Since the late 1980s, an important current labelled "postmodern" has swept through British geography and deeply affected its orientations. Postmodernism can be summed up as two main trends. One, whose critical description is the main object of this article, consists in identifying the main characteristics of our epoch which are credited with attributes distinct from those of modernity. In this perspective, the aim is to diagnose the transition to a cultural logic of dilution and cross-fertilisation of references instead of the modem logic of separation and classification. This first side of postmodernism still makes use of the established methodology of scientific enquiry. However it implies the notion that to a new era should correspond new thinking modes. It is precisely this attempt at « thinking differently » which constitutes the other side of postmodernism as breaking away from the modem scientific concept. Its description will be the object of a second article in the next issue of the journal.