From time to time, not very often, it looks as though the world has given philosophy a job to do. Now is such a moment. At last, a big abstract noun – truth – is at the heart of a cultural crisis and philosophers can be called in to sort it out.
Send them back. Philosophers’ problems with truth are not the same as the world’s. The post-truth debate cannot be readily fixed by a better theory. Most of the time, people are clear enough what makes something true. To use Alfred Tarski’s famous example from the 1930s, “Snow is white” is true if and only if snow is white. If that sounds obvious, that’s the point. A statement is true if and only if it corresponds to a state of affairs or event that obtains in the world.
This and other “correspondence theories of truth” are now out of fashion in philosophy. Pragmatism has long been more influential in America, which in crude terms is the idea that to say something is true is to say that it works to assume it is true. True beliefs took humans to the moon, false ones led to a space shuttle exploding shortly after take-off. Coherence theories see truth as a property of collections of propositions, not of individual ones alone: the truths of 2+2=4 depends on a whole number of assumptions not captured in that simple sum. Redundancy theories more or less do away with the need to talk about truth. You don’d add anything to a statement like “Paris is the capital of France” by prefacing it with “It is true that . . .”.
The merits of these competing theories are of mainly academic concern. When people debate whether there were weapons of mass destruction in Saddam Hussain’s Iraq, whether global warming is real and anthropogenic, or whether austerity is necessary, their disagreements are not the consequence of competing theories of truth. No witness need ask a judge which theory she has in mind when asked to promise to tell the truth, the whole truth and nothing but the truth.
Why then has truth become so problematic in the world outside academic philosophy? One reason is that there is major disagreement and uncertainty concerning what counts as a reliable source of truth. For most of human history, there was some stable combination of trust in religious texts and leaders, learned experts and the enduring folk wisdom called common sense. Now, it seems, virtually nothing is universally taken as an authority. This leaves us having to pick our own experts or simply to trust our guts.