I've been seeing so many people complain about Dr. Peterson's understanding of postmodern doctrine. I recently took a college class on postmodern philosophy and came to realize that very few people actually understand the philosophy.
I'm not going to write up a comprehensive history of philosophy starting from Hegel and Kant, or delve into the intricacies of individual contemporary postmodern thinkers like Derrida, Foucault, et al., since this is not an intellectual exercise. Instead, I'm going to contrast the most important beliefs of enlightenment and postmodern philosophy, since postmodernism is a direct reaction to the former.
Enlightenment
Knowledge: Objective knowledge is possible.
Truth: Universal truths exist independent of individual minds/societies.
Reason: Reason is used to gain/justify knowledge of the world.
Goal: Progress is made by thinking rationally in relation to objective knowledge.
Postmodernism
Skepticism: It's impossible to have objective knowledge (e.g. our senses are easily fooled).
Relativism: No absolute truths. They (the truths) are only social constructs based on gender, race, etc. created for the purposes of power. Language is a big source of oppression. (Structuralist beliefs are a bit more complicated.)
Rejection of grand narratives/theories/ideologies: Since postmodernists are relativists, they are opposed to single all-encompassing narratives. (This is humorous since all postmodernists are skewed to particular ideologies but are opposed to religion.)
Denial of reason/logocentrism: Reason is used by the powerful to oppress the weak. Emotions/experiences of the oppressed are more valid and grounded in reality than logocentrism.
Goal: Progress is made by fighting oppression through the exposure of meta-narratives that are used by the powerful to oppress the weak. (Postmodernists love the word hegemony.)