Earlier quoted context omitted.
Modernism is Descartes` "I will find a single indisputable axiom and can prove everything knowable from there." His axiom? "Cogito ergo sum." Postmodernism is rooted in the notion that there is no indisputable base axiom from which we can build our understanding of the world. It's unprovable assumptions all the way down. The consequences for this, if you accept it (you don't have to, but you're going to have a hell o…
If you subscribe to postmodernism then there is no such thing as an 'irrational' claim. All of the observations and logic another person may be using to make the claim are all equally likely to be valid/invalid and claiming otherwise is just forcing your opinions of truth on them.
The fact that no axiom stands by itself does not change the fact that when you subscribe to a set of axioms, you can't deny their consequences. What is rational merely changes, and honestly, the older definition always felt kind of crazy.