This post summarizes my notes on two secondary sources on postmodernism -- reviewed here and here. I am not documenting every statement. Consult the sources I have cited. In a much later post I will summarize my notes on Richard Rorty (1931-2007), perhaps including his book Philosophy and the Mirror of Nature, as an example primary source.
WHAT IS POSTMODERNISM?. Postmodernism is an anti-worldview worldview. Postmodernists reject systematization in both philosophy and religion (specifically theology), but the pieces of their implicit worldview can be assembled into an explicit worldview. It is neither a philosophy (distinguished by at least a claim to use reason in developing it) nor a religion (distinguished by reliance on mysticism). It is, I think, best described as a creed of radical skepticism, the claim that we can know nothing.
Postmodernism's advocates started to appear as the worldwide socialist movement began to falter, and evidence for socialism's inevitable failure began to accumulate in the USSR, China, and elsewhere. The "leading strategists" of the postmodernist movement -- the social movement advocating postmodernism and applying it to contemporary culture -- were Jacques Derrida, Michael Foucault, Jean-François Lyotard, and Richard Rorty. (Hicks, p. 1) Other postmodernists have specialized in particular fields such as architecture or psychology. For example, "[t]he architectural theorist Charles Jencks [b. 1939] has done more than anyone else to popularize postmodernism as a theoretical concept, particularly in a series of editions of his best-known book The Language of Post-modern Architecture (1st ed., 1977)." (Sim, 3rd ed., p. viii)
POMO TARGETS. One way to characterize postmodernism is by identifying its targets. Postmodernism is anti-modernism, where "modernism" means a collection of the most objective ideas of the Enlightenment period (c. 1700-1800) and their positive effects on 19th and 20th Century culture (especially in law, business, technology, and science). In philosophically hierarchical order, postmodernism's fundamental targets are:
- In metaphysics, naturalism (the idea that everything has a definite nature).
- In epistemology, reason (the faculty of understanding the nature of things, through observation and logical thought) and products of reason such as particular, integrated systems of thought, which postmodernists call "meta-narratives"). (Sim, pp. 272-273)
- In theory of man, the individual is born tabula rasa.
- In ethics, individualism.
- In politics, capitalism.
POMO PRINCIPLES. In direct opposition to its targets, postmodernism supports these ideas:
- In metaphysics, anti-naturalism, that is, the belief that we should not expect everything to have a definite, identifiable nature.
- In epistemology, linguistic social subjectivism, the idea that the language each of us learns from the society around us determines our view of reality.
- In theory of man, social determinism, the idea that individuals are constructed by their society.
- In ethics, collectivism, the belief that the individual is foremost a unit of a collective.
- In politics, socialism. (Hicks, pp. 5-15, for targets and principles)
These fundamental principles lead to particular themes advocated by specialized postmodernists. One example is an academic position such as "deconstruction," a form of literary criticism in which the postmodernist reader claims to discover multiple meanings in a particular text, meanings that the author may not have intended. (Sim, pp. 245-246). A second example is a cultural (ultimately political) theme such as denigration of Christopher Columbus. (Hicks, pp. 18)
WHAT ARE ITS HISTORICAL ORIGINS? The fundamental elements of the culture of the Enlightenment (c. 1700-1800, in Western Europe) -- its naturalism, devotion to reason, and individualism -- were a seedbed. From that seedbed, modernism grew, particularly in Anglo-American culture. Enlightenment values and incipient modernist values provoked an anti-Enlightenment reaction among mystics, particularly in Germany. (French culture was mixed.) That reaction eventually fueled postmodernism. (Hicks, pp. 21-22 and 24-29)
The two main roots of the Counter-Enlightenment were Rousseau (1712-1778) and Kant (1724-1804). Rousseau contributed a collectivist social philosophy. (Hicks, pp. 99, 100, 106, 108, and 109) Kant undermined reason. (Hicks, pp. 27-42)
The anti-Enlightenment road ran from Kant (and to a lesser extent, Hume, 1711-1776) through Hegel (1770-1831), Schopenhauer (1788-1860), Kierkegaard (1813-1855), Marx (1818-1883), Nietzsche (1844-1900), Heidegger (1889-1976), and Wittgenstein (1889-1951) to primary postmodernists -- Lyotard (1924-1998), Foucault (1926-1984), Derrida (1930-2004), and Rorty (1931-2007) -- and then to secondary postmodernists in our time. (Hicks, pp. 21-22, plus Chs. 2 and 3)
WHAT IS THE POSTMODERNIST VIEW OF REASON?. Reason is the faculty of perceiving things in reality and conceptualizing their nature. At its most fundamental level, the postmodernist rejection of reason is metaphysical: Postmodernists reject the idea that things have a nature. (Hicks, p. 2, citing Foucault and Rorty) This position immediately undercuts reason.
For some postmodernists, the justification for rejecting reason is political. Western Civilization -- defined philosophically as a complex of cultural elements, such as science and objective law, that grow from a foundation of reason -- oppresses women, homosexuals, the poor, and nonwhites, the postmodernists say. Therefore, to oppose oppression, postmodernists oppose its foundation in reason. (Hicks, p. 3)
Other postmodernist attacks on reason appear in different forms. One is polylogism, though postmodernists apparently do not use that term. Postmodernists hold one's class, race, wealth, or sex to be a guiding factor in interpreting the world and in deciding what actions -- especially political ones -- to take. (Hicks, pp.15-16)
Still other postmodernists purportedly do not completely reject reason or its applications, such as the scientific method, but propose "alternatives," which means mysticism in some form. (Hicks, p. 17)
WHAT IS THE POSTMODERNIST VIEW OF MYSTICISM?. Postmodernists are not usually outspoken champions of mysticism in its various forms (faith, revelation, intuition, and so forth). Rather, they support mysticism indirectly. For some postmodernist writers, their style of writing is their statement of support for mysticism. Their styles are generally not comprehensible; reason can learn nothing in reading nonsense. (Try "reading" Derrida, Of Grammatology.)
Other postmodernists seemingly do write clearly, but they supplant reason with some other persuasive value such as "attractiveness," as when Richard Rorty says:
Conforming to my own [postmodernist] precepts, I am not going to offer arguments against the [modernist] vocabulary I want to replace. Instead, I am going to try to make the vocabulary I favor look attractive by showing how it may be used to describe a variety of topics. (Quoted by Hicks, p. 177)
Some religious mystics, particularly those who are members of the emerging Christian Radical Orthodoxy movement, have embraced postmodernism "as a critique of a particular secular framework, that of universal reason." (Pamela Sue Anderson in Sim, p. 80) The distintegration of thought brought by postmodernist skepticism creates a vacuum that religious "meta-narratives" (worldviews) fill with conventional forms of mysticism (revelation, faith, traditionalism, and reliance on holy scripture).
CONCLUSION. The general payoff of postmodernism is disintegration of reason and all the values that grow from it; mysticism rushes in where reason dies. There is also a particular payoff of postmodernist attempts to supplant reason with mysticism. In Stephen Hicks's words, postmodernists can use their rejection of reason "to justify the personal leap of faith necessary to continue believing in socialism" despite the accumulating historical evidence of socialism's failure. (Hicks, pp. 179 and181)
Author, The Power and the Glory: The Key Ideas and Crusading Lives of Eight Debaters of Reason vs. Faith, at http://www.reasonversusmysticism.com
 In addition to Stephen R. C. Hicks, Explaining Postmodernism: Skepticism and Socialism from Rousseau to Foucault, 2nd ed., and Stuart Sim, The Routledge Companion to Postmodernism, 3rd ed., another general, introductory resource is: Gayl Aylesworth, "Postmodernism," The Stanford Encyclopedia of Philosophy, Winter 2010 edition, http://plato.stanford.edu/entries/postmodernism/.
 Hicks, EP:SSRF, shows the assembled result, particularly in Ch. 1. For other, but lightly critical discussions by postmodernists about postmodernists' views of religion: Pamela Sue Anderson, "Postmodernism and Religion," in RCP, Ch. 7. For their views on philosophy: Stuart Sim, "Postmodernism and Philosophy," in Sim, editor, RCP, Ch. 1.