John Nerst, Postmodernism vs. The Pomoid Cluster, Areo, June 30, 2018. There is this, by way of initial definition:
Postmodernism is more complicated than it appears, and its details exceed my own knowledge and certainly what can be discussed here. Nevertheless, the most important thing about postmodernism is right there in the name. Post–modernism. It comes after and must be understood as a reaction to modernism. Modernism itself emerged out of premodernism. In the broadest terms, this trio of words is about the social order and the ideas that describe, govern, and constitute it.
In premodernity, the social order and the nature of the world were one and the same and taken for granted. They were handed down to us by tradition, not options for us to engineer. Modernity upended all that. From the Renaissance on, through the increasing importance of science, the Enlightenment, and the Industrial Revolution, the world changed, and our ideas changed with it. Along with the natural world, the social order was now the object of reason and critique, of control and systematization. This enables, or even ensures, progress with a capital P. But progress has its limits, everything doesn’t get better cost-free, and it isn’t a given carried by historical momentum. There are pitfalls. Things haven’t always been as easy as they appear. Enter postmodernism.
Postmodernism is the disillusion with and the critique of the whole of the modernist project and its assumptions. Progress is not a given, not a law of nature. We can’t answer all questions with science, and no one framework correctly describes society and history. In essence, postmodernism is the idea that there is no one true method, model, ideology, or narrative with the right to dictate facts and mold the social order. Not Christianity, not science, not dialectical materialism. Nothing.
Postmodernism isn’t so much an ideology, a framework, or a system of thought as it is the rejection of ideologies, frameworks, and systems of thought.
And then Nerst works toward an understanding of how "postmodernism" becomes stripped of its substantive intellectual content in the process of popularization:
This article by Matt McManus is illustrative. He argues that lumping Marxism and postmodernism together makes no sense at all and supports this by describing some profound differences between them. He’s right, of course, but the argument misses its target by assuming that all uses of “Marxism” or “postmodern” are meant in a fully detailed, technical sense. Instead, these terms tend to be used like normal words often are: semi-metaphorically, with only some of their properties and associations active. It’s like calling some sad thing a “tragedy,” even though, strictly speaking, it isn’t a Greek morality play that ends with the protagonist in ruin due to a fatal character flaw.