The greatest postmodern writers were the Marquis de Sade and Miguel de Cervantes. Jan Potocki was also a genius. When one considers these and many other authors (even Shakespeare has a postmodern side, but I hate to reduce him by trying to contain him within this category), it becomes clear that postmodernism preceded modernism.
I'm speaking a little tongue-in-cheek, but my real point is that there is no clear or unambiguous division between modernism and postmodernism. The idea that we are living in a "postmodern age" that is characterized by the "postmodern condition" is simply nonsense. Actually, it is not even nonsense - that would be a bit of compliment. It is simply false. Art textbooks nowadays will say something like postmodernism began in the 60s or the 50s or the 40s - some time in the mid-twentieth century. Well, if we look at "postmodern culture" before and after these dates, what we discover is that... nothing changed. There is nothing that we can find in the so-called "postmodern period" that we cannot find precursors for in the "modern period." Postmodernism is simply the repetition of modernism (with, perhaps, all of the Kierkegaardian implications of "repetition"). If I were in a less charitable mood, I might say that postmodernism is simply modernism, but not as good. For instance, is there any postmodernist who is better - or even more "postmodern" - than that arch-modernist, James Joyce? I have already said that postmodernism is when the wind gave out in the sails of modernism - the doldrums.
The declaration of a postmodern age is a pure "locutionary act," to
borrow a term from J.L. Austin - that is, it has no material meaning
that can be measured or detected or experienced apart from the
declaration itself. If it is true, it is only true because people say
so. Well, I don't say so. I say modernism never ended, because the contradiction that gave rise to modernism was never resolved.
For the sake of argument, let's accept the notion of a "postmodern culture" that existed from some time in the mid-twentieth century until 1992. The beginning of this period is completely unclear - a boundary that is impossible to draw. If anything, the end-boundary is far clearer.
If there is anything that characterizes this period, which has come to be known as the postmodern period, it is this: postmodernism is cultural logic of detente.