Postmodernism begins with a loss of faith in the dreams of modernism.
Modernism is the mindset that emerged during the Enlightenment, an optimistic faith in the idea that methodology of science can lead the human sciences to meaningful psychological understanding of people. Postmodernism begins, as Lyotard said, with an incredulity towards our cultural metanarratives, and a major metanarrative, especially in psychology, is individual difference theory. But postmodernism does not replace this modernist dream and all its metanarratives with another metanarrative. In place of the lost dream of modernism, postmodernism gives us a new vocabulary, a new language game, for helping us notice dimensions of experience that were obscured by the modernist vision. It's a dynamic language game, with meanings evolving and changing.