(Aristotle) If anyone thinks nothing is to be known, he does not even know whether that can be known, as he says he knows nothing.
(Charles Darwin, Introduction to The Descent of Man, 1871) I have quoted another very good summary of postmodernism below (that relates to this skepticism), with two important comments added.
Postmodernism is a general and wide-ranging term which is applied to literature, art, philosophy, architecture, fiction, and cultural and literary criticism, among others.
This extreme skepticism, of which Friedrich Nietzsche, Ludwig Wittgenstein, Karl Popper and Thomas Kuhn are particularly famous, assumes that; a) All truth is limited, approximate, and is constantly evolving (Nietzsche, Kuhn, Popper).
b) No theory can ever be proved true - we can only show that a theory is false (Popper).
The ONLY ABSOLUTE TRUTH is that there are NO ABSOLUTE TRUTHS (Feyerabend) I define postmodern as incredulity toward metanarratives ...
(Jean-François Lyotard) Finally, if nothing can be truly asserted, even the following claim would be false, the claim that there is no true assertion.c) No theory can ever explain all things consistently (Godel's incompleteness theorem).d) There is always a separation between our mind & ideas of things and the thing in itself (Kant).That the modernist tradition of progress and ceaseless extension of the frontiers of innovation are now dead. Like it or not, we humans are stuck in a permanent crisis of meaning, a dark room from which we can never escape.(Kalle Lasn & Bruce Grierson, A Malignant Sadness) The post-modern understanding that our language is too imprecise, our senses too limited and deceptive to ever absolutely describe Reality has been caused by the failure of physicists and philosophers (over many centuries) to discover / correctly describe Reality.The correct position must be one of open minded skepticism - that without true knowledge of reality then all our knowledge of the external world of our senses is uncertain.So postmodernism cannot say whether we can or cannot know reality / absolute truths - as it has no foundation to deduce absolute truths from.Postmodernism relies on concrete experience over abstract principles, knowing always that the outcome of one's own experience will necessarily be fallible and relative, rather than certain and universal.Postmodernism is "post" because it is denies the existence of any ultimate principles, and it lacks the optimism of there being a scientific, philosophical, or religious truth which will explain everything for everybody - a characteristic of the so-called "modern" mind.It’s allusive to the point of being impossible to articulate.But what this philosophy basically says is that we’ve reached an endpoint in human history. All religions and utopian visions are dead and resistance to the status quo is impossible because revolution too is now dead.