"What is truth, says jesting Pilate, and does not stay to hear."

That moment in biblical history, captured by the 16th-century English philosopher Francis Bacon, remains a call to speak the truth in the face of denial.

Yet, Pontius Pilate at least asks what the truth is: He does not dismiss its possibility. That task has fallen on the jesters of today.

They are the governors of the post-truth world. It is a world where the boundless affiliations of emotion matter more than the raw boundaries of fact, where manipulation by big data and social media distorts the funxctioning of the mind. Combined with outright conspiracy theories, these trends pretend to advance the individual's quest for freedom and knowledge, but they only undermine trust in any kind of authority - without offering an alternative.

In a world where truth is devalued, the moral and political stakes that humans have in the contest of ideas is reduced to shadow play. There is no core of truth to which humans can anchor themselves so as to invest their lives with the wider significance of common, shared and universal meaning.

How the absence of belief in truth impoverishes personal and social lives is revealed in an important book published this year by the British scholar-journalist Matthew D'Ancona. Truth, he observes, is society's "reserve currency". Hence, the "crash in the value of truth" is "comparable to the collapse of a currency or a stock", he writes in Post-Truth: The New War On Truth And How To Fight Back.

A decline in the value of truth undermines the trust that a society places in honest people, and "all successful societies rely upon a relatively high degree of honesty to preserve order, uphold the law, hold the powerful to account and generate prosperity".

Of course, no one would deny the need for scepticism, whether in philosophical or in public life. What is unhealthy is to deny the possibility of truth itself and hence of building viable social structures based on it.

On the political front, when feelings outweigh the agency of facts, citizens stop demanding truth from their politicians. Instead, they support those whose political positions amplify the narrow range of their own opinions, preferences and prejudices. Thus, post-truth politics represents the "triumph of the visceral over the rational, the deceptively simple over the honestly complex".

D'Ancona makes these distinctions excellently, giving in the process a definition of post-truth: the "infectious spread of pernicious relativism disguised as legitimate scepticism". He traces the proximate origins of this to the post-modern movement, whose questioning of objective reality helped to corrode the very notion of truth. In a sense, post-modernism may be considered the greatest one-night intellectual stand ever achieved in history.

The astonishing ascendancy of American President Donald Trump symbolises the political zenith of a troubled age. Its characteristic spirit is captured unintendedly in the phenomenon of "alternative facts". That is a term which a member of his administration used to justify an interpretation of events that flew in the face of verifiable reality.

What is more alarming than the discovery of alternative facts is that large chunks of an educated and politically conscious American citizenry have acquiesced in the use of that term. They appear to not care about the veracity of words so long as they advance the political cause of a leader whom they support.

In fascist and communist systems, large numbers of citizens pretended to adhere to a wicked or failing ideology in which they did not believe. They did so because they feared the state or found it politic to keep in step with prevailing opinion, generated by the incessant propaganda of an all-powerful state. That was post-truth from above and around. It was bad enough.

What is worse is post-truth from below: a citizen's desire to lie to himself because to do otherwise would be to demand that he act as a responsible member of political society. D'Ancona provides another wonderful definition here. A modern pluralist society is one "composed of multiple communities that could co-exist, driven by the hope of a better life in negotiated harmony".

From San Francisco to Singapore, this is the crucial challenge. Along with fact-checking organisations, it is people who must learn to navigate the Web discerningly as they seek opinions on which to base their political and moral choices. The civic spirit must remain a line of defiant resistance to the purveyors of political untruths, half-truths and outright lies. Voters must act out of the enlightened self-interest that comes from seeing society as an extension of the individual, as his/her completion and protection. Only then can post-truth be fought back.

The mainstream media must help to nurture these abiding habits of the heart and the mind. After all, there was truth before post-truth, and there can be truth again.

Although the scourge of fake news precedes the remarkable advent of alternative facts, the two phenomena are related intrinsically. In a world where truth recedes as the language of social communication, fake news ceases to sound fake. It makes sense.

Therein lies the danger. Fake news could cause massive damage. It could start war or spark civil war, bring economic systems to their knees, and spell the end of an information order in which news must have at least some connection with a socially shared sense of reality in order to be credible.

An example of fake news is the campaign for Britain to leave the European Union.

It employed spurious statistics with breathtaking audacity, lying that Brexit would yield £350 million (S$614 million) a week to Britain's National Health Service.

Once Britain had voted to leave the union, that claim vanished into thin air, and impressionable voters were left millions poorer in delusional savings.

What is terrifying is not that outcome. It is how British voters who were swayed by the Leave campaign did not unleash their fury on it for having misled them. Instead, the missing pounds were dismissed with indulgent forgiveness. Like alternative facts, the £350 million became alternative news.

Will Singaporeans be discerning when the time arrives to face up to post-truth? It is unlikely, since human nature is more or less the same everywhere. However, we have been warned by events in Britain and America.

Let us not lose heart. Truth survives time. Pontius Pilate prevented Jesus Christ from answering his question but, in the process, a lasting religious revolution arrived in human history. And no one would remember Pilate washing his hands were it not for the truth that stuck to his fingers.

•The writer is a former Straits Times journalist.