by Emrys Westacott
How does one criticize and resist politicians who have zero concern for truth? 
Obviously, Trump is not the first politician to tell whoppers. Politicians who are in the pockets of the banks, the oil companies, tobacco, pharmaceuticals, weapons manufacturers, and so on have long suppressed, denied, or bent the truth for reasons of self-interest. But the brazenness of the lying is unusual. In normal, rational, civilized discourse, there are background conventions understood by all parties. According to philosophers like Paul Grice and Jürgen Habermas, these provide a framework that makes most ordinary communication possible. One of these conventions is that what we say is supposed to be true. Another is that we are supposed to be sincere. There are contexts where these conventions may not hold in the usual way–e.g. when we are haggling at a yard sale–but most of the time they are in place. Imagine how it would be if they weren't? If you were to ask someone for directions or for the time, you couldn't assume they'd try to tell you the truth. So in such a world you would never bother asking. Without assumptions of this sort in place, the most banal conversations would become pointless since we'd have no reason to think that anything being said was tethered to reality.
The gold standard regarding rational discourse is science, which prides itself on its disinterested search for objective truth. But the same conventions operate in many other spheres. Historians, journalists, judges, and sports commentators, all feel the same obligation to respect hard evidence and eschew contradictions.