It’s not that obvious
It a truly postmodern fashion, definitions of postmodernism are troublesome. I had difficulties with Postmodernism and its Critics. The page is put together by students, quoting secondary sources. It’s amazing to me to think that anthropologists think that the “modern” began in the renaissance.
For literature folks, the distinctions are much finer. Modernism began somewhere in the 1890s, and there is some dispute if it’s really over at all. It depends on your definition of postmodernism. According to the Encyclopedia of Literary Theory, in my field anyway, the postmodern begins around 1960 in works that “display certain characteristics such as reflexivity, irony and a mixing of popular and high art forms.” The difficulty of the definition is elaborated thusly:
Either seen as a continuation of the more radical aspects of modernism or as marking a rupture with such things as modernist ahistoricism or yearning for closure, postmodernism has been linked to “the cultural logic of late capitalism (Jameson); the general condition of knowledge in times of technology (Lyotard); the replacing of a modernist epistemological focus with an ontological one (McHale); and the substitution of the of the simulacrum for the real (Baudrillard). Postmodern literature has been called a literature of replenishment (Barth), on one hand, and the literature of an inflationary economy (Newman) on the other. In short, there is little agreement on the reasons for its existence or on the evaluation of its effects.
So what does that all mean? Mostly, it means that as periods go, it is nearly impossible to define, and to push the onset of modernism back to the renaissance really confuses things. Taking up the assertions of Lytoard in The Postmodern Condition is probably the easiest place to start. Technology changes things, that seems to go without saying. Derrida is tougher, but not impenetrable. In order to explain where Derrida, de Man and the deconstructive bunch are really coming from it’s important to have a handle on structuralism. A single page or short definition won’t do it. Postmodern theory is a bunch of different folks, saying a bunch of different stuff.
Here’s my take, for what it’s worth. Technology gravitates into systems. All systems have a central organizing principle. Humanity has been searching for organizing principles for a long time. One by one, these organizing principles have been found to be flawed. To disrupt the system by removing the center of the system, is to set it into flux, or freeplay. That’s deconstruction, or to use de Man’s term, the system is demystified. Some, like Derrida, feel that there can be no mythic organizing principle that cannot be removed. To be postmodern, perhaps, is to doubt everything. However a few, like Habermas and Ricouer, suspect that there is an underlying center, a linguistic one, that allows for generalized theory. I like Zigmunt Bauman’s metaphor for the postmodern condition: liquid modernity, a flux that can be poured into a container that is continually shifting in shape, due to the constant failure of systems.
Clear as mud? How about this: postmodernism is a buzzword for a dozen or more competing ways of describing the mess we’re in right now.