I will use the term modern to designate any science that legitimates itself with reference to a metadiscourse of this kind making an explicit appeal to some grand narrative, such as the dialectics of Spirit, the hermeneutics of meaning, the emancipation of the rational or working subject, or the creation of wealth.
... Simplifying to the extreme, I define postmodern as incredulity toward metanarratives. This incredulity is undoubtedly a product of progress in the sciences: but that progress in turn presupposes it. To the obsolescence of the metanarrative apparatus of legitimation corresponds, most notably, the crisis of metaphysical philosophy and of the university institutions which in the past relied on it. The narrative function is losing its functors, its great hero, its great dangers, its great voyages, its great goal. It is being dispersed in clouds of narrative language elements ...
Lyotard, Jean-Francois 1984, The Postmodern Condition: A Report on Knowledge, trs. Geoff Bennington and Brian Massumi, University of Minnesota Press, Minneapolis, Minnesota, Foreword by Fredric Jameson: xxiii-xxiv.
John Frow on Postmodernism
But rather than try to unravel the "meaning" of the concept of postmodernism, let me suggest that the word can be taken as designating nothing more and nothing less than a genre of theoretical writing.
Frow, John 1991, What was Postmodernism? Local Consumption Publications, Sydney: 3
David Harvey on Brian McHale on the 'postmodernism novel'
The postmodern novel, McHale (1987) argues, is characterized by a shift from an 'epistemological' to an 'ontological' dominant. By this he means a shift from the kind of perspectivism that allowed the modernist to get a better bearing on the meaning of a complex but nevertheless singular reality, to the foregrounding of questions as to how radically different realities may coexist, collide, and interpenetrate.
Harvey, David 1989, The Condition of Postmodernity: An Enquiry into the Conditions of Cultural Change, Blackwell, Oxford: 41; referring to Brian McHale 1987, Postmodernist Fiction, Methuen, New York & London; repr: McHale, Brian 1989, Postmodernist Fiction, Routledge, New York & London.