Lytorad mantains that the horror of Aushwitz, which is realt but not rational, falsifies the fundamental assumption fo Hefel "what is real is rational": And yet even Auschwitz has a meaning: it is a lesson about what is the absolute eveil, and I dare say that humankind has largely learned the lesson. It was not necessary: had man be more wise and less terrified by communism Hitler could have been avoided - nothing is stricltly necessary, and the idea of Lyotard arises from the confusion between rationality and necessity. Two or more outcomes can follow logically from a single cause, and many causes can lead to a single outcome. In quantum mechanics - which has the rationality and rigour of mathematics - many - usually even infinte - outcomes are possible, differently from the unique consequences of a cause in classical mechanics.
Post-modernism realizes that the solution of an equation can not be unique, that the world is a mutliverse, and yet it does not realize fully the consequences of this shift of paradigm - which can happen only with the shift to the systemic or complex thinking. Paradoxically, systemic thinking is much easier from a the point of departure of dialectic - at least this is my personal experience