The essence of postmodernism could be stated, ignoring the irony, as the rejection of classical and modern thought that attempts to attribute anything with an objective meaning or truth. To quote the Urban Dictionary, “The postmodernist critique removes that central concept, it “decenters” the system of meaning. Postmodernism points out that all systems of meaning are in constant negotiation and flux, therefore claims of transcendant morality are suspect.”
Recognizing the irony, however, makes it impossible to say that the essence of postmodernism is anything as it is a critique of essence.
For me this means that there are two main types of postmodern critique in academic and theoretical circles – a practically useful one and a practically useless one. The practically useless one rests on the notion that the pervasiveness of subjectivity negates any attempt to find truth. The practically useful one recognizes that subjectivity pervades our notion of truth and our reliance on dichotomy, but uses the critique to unpack the assumptions and controls of the power structures responsible for creating those notions and reliances in order to reveal the harm those required, and potentially move us to positions where those harms can be minimized or even repaired.