We can now add modern shapers of belief such as conformational bias, brainwashing and the whole panoply of techniques of persuasion by advertising.
The trouble with these ways of forming beliefs is that they do not appeal to evidence and they are not reliable for the truth of what is believed. Worse, we can pick up false beliefs, as the prevalence of fake news shows.
Which way do we want beliefs of others and ourselves to be formed? Shockingly, there might be no shame in showing one's beliefs are not based on evidence or are due to non-rational factors. The dismal prospect of the post-truth era is beliefs that are indifferent to truth or falsity but might be, say, power-enhancing.
As an illustration, pick your own favourite post-truth which has become prominent in the "Brexit" referendum or the US presidential election. There was the bus in the UK emblazoned with the false claim "we send the EU 350 million a week". Fact checking showed that to be wrong and even Nigel Farage eventually stepped away from the claim. There was the Trump "birther" claim that Obama was not a US citizen. Eventually, he grudgingly backtracked on this.
In both these cases there is a truth to be found, and evidence and argument play their important role in showing such claims to be false. But doing this might require some courage on the part of the investigator exposing the falsehood.
And it might require institutional arrangements which help us track the truth (such as newspapers committed to accuracy in reporting and to providing argued evidence).
A more sinister aspect of post-truth is not merely that evidence can be ignored; rather there is allegedly no truth to consider.
In my own subject, philosophy, there is, on the whole, a very healthy debate about the nature of truth. But unfortunately there is also a sinister underbelly of "post-truther" views which have prominence well beyond their merit. Readers may not be aware of them, so here are a few.
The US philosopher Richard Rorty, a darling of postmodernists and followers of the French philosopher Jacques Derrida, claimed that the truth is what your contemporaries will let you get away with. Not so. Tell that to Galileo, who said that the Earth moved but was put under house arrest by his contemporaries.
Notoriously the 19-century German philosopher Friedrich Nietzsche said "truth is an error" and "there are no facts but only interpretations". Commentators have bent over backwards trying to "interpret" him. A riposte might be: are you claiming it is a fact that there are no facts?
Nietzsche is an advocate of the "will to power" and has softened us up for the Trump post-truth era. A Trump surrogate, Scottie Nell Hughes, tells us: "There's no such thing, unfortunately, any more, of facts." Illiterate, but very Nietzschean.
Insofar as studies in humanities have not resisted the views of post-truthers, too bad for humanities. But what of science? It would be quite alien for science to reject the search for truth and evidence, the core of its critical methods.
In science we have models of what the rational approach to believing ought to be. If followed, they are an important way to keep the post-truth era from engulfing us.
