We're probably post-narrative and post-lexical (words) but haven't become aware of what to possibly update these tools with. Post-truth is an abstraction rooted in the arbitrary.
Reality is specific. Actions, materials. Words and language are arbitrary, they're processes, and they're simulations. They don't reference things, they represent them in metaphors, so sure they have "meaning" but the meanings reduce the specifics in reality which have many times the meaning possibility to linearity, cause and effect. That's not conforming to the reality that exists, that's severely reducing, even dumbing down reality.
There is a reality which exists. Words have meaning. Words are more or less true as the meaning they convey conforms more or less well to the reality that exists. So no, truth is not rooted in the arbitrary. Quite the opposite.
Or at least, words had meaning. As we become post-lexical, it becomes harder to tell how well any sequence of words corresponds to reality. This is post truth - not that there is no reality, but that we no longer can judge the truth content of a statement. And that's a huge problem, both for our own thought life, and for society.
Words are merely wax fruit metaphors for meaning, they aren't meaningful in and of themselves. That's how dictionaries exist. Any reality understood from words is mere simulation.
Reality is specific. Actions, materials. Words and language are arbitrary, they're processes, and they're simulations. They don't reference things, they represent them in metaphors, so sure they have "meaning" but the meanings reduce the specifics in reality which have many times the meaning possibility to linearity, cause and effect. That's not conforming to the reality that exists, that's severely reducing, even dumbing down reality.