For as long as there have been politicians, they have lied, fabricated and deceived. The manufacture of falsehood has changed over time, as the machinery becomes more sophisticated. Straight lies give way to sinuous spin, and open dishonesty disappears behind Newspeak and Doublethink. However, even if honesty is sometimes the best policy, politics is addressed to people’s opinions, and the manipulation of opinion is what it is all about. Plato held truth to be the goal of philosophy and the ultimate standard that disciplines the soul. But even he acknowledged that people cannot take very much of it, and that peaceful government depends on ‘the noble lie’.

Nevertheless, commentators are beginning to tell us that something has changed in the past few years. It is not that politicians have ceased to tell lies or to pretend that the facts are other than they are; it is rather that they have begun to speak as though there is no such distinction between facts and fabrications. We live in a post-truth world — such is the mantra. Two books entitled Post Truth have just appeared, explaining the matter, one by Matthew d’Ancona and one by Evan Davis — highly articulate writers with an urgent message for our times. For d’Ancona the post-truth culture explains much that troubles him in public life, not least the election of President Trump and the Brexit vote. Evan Davis, writing about what he calls ‘peak bullshit’, concurs. Somehow the boundaries between true and false, sense and nonsense, opinion and reality, thought and bullshit have been erased, and no one really knows how to reinstate them.

That is one way in which the Brexit vote is explained by those who cannot stomach it. If there is no truth, then opinions are no longer true or false, but simply yours or mine, ours or theirs. And since the Brexit vote was about identity, ‘we’ were bound to win over those who still thought there was something to argue about. As for the ‘experts’, why should we listen to them, when they were trying to phrase the argument in a language that no longer applies, as though there were some objective ‘fact of the matter’ that we could all agree upon?

I regret that a writer as intelligent and imaginative as Matthew d’Ancona chooses to dismiss the Brexit vote in that way. But I recognise that, when it comes to President Trump, he definitely has a point. This extraordinary person, whose thoughts seem shaped by their very nature to the 140 characters of a tweet, makes no distinction between the true and the false and assumes that no one else makes such a distinction either. Should the FBI show that Trump colluded with the Russians in manipulating the presidential election, that would not be a fact, but simply ‘fake news’, of no greater authority than his own homegrown alternative, which will have the added advantage of being contained in 140 characters, so that we can read it quickly and move on. (For what it is worth, though, I would say that Vladimir Putin and Recep Erdogan are ahead of Mr Trump in the post-truth stakes.)

You might respond to this by saying that Trump is an aberration, and that the idea of a post-truth culture, of which he is simply one alarming representative, is itself a fabrication, another item of fake news. Neither d’Ancona nor Davis takes that line, and there are reasons for agreeing with them. The concept of truth has been the victim of massive cyber-attacks in recent decades, and it has not yet recovered. The most recent attack has come from social media, which has turned the internet into one great seething cauldron of opinions, most of them anonymous, in which every kind of malice and fantasy swamps the still small voice of humanity and truth. Mr Trump is a creation of social media, and he has an astute way of using his smartphone to bypass all the filters designed to exclude people like him from high office.

We have yet to get used to this, and to the damage social media has done to the practice of rational argument. Maybe someone will discover the software that will worm through the system, systematically deleting all that is false and destructive. Even if that can be achieved, however, it won’t undo the damage of the previous great cyber-attack, which came from the intellectuals themselves, when they rushed to discard the idea of truth as an obstacle to an academic career. It is to d’Ancona’s credit that he recognises that the post-truth culture swept through the academy a whole decade before the internet began, cramming the syllabus with unreadable nonsense from Deleuze and Baudrillard, and ensuring that no humanities student would ever again read a book for pleasure.

You could blame Nietzsche, whose declaration that ‘there are no truths, only interpretations’ has made him into the highest authority among post-modern academics. But Nietzsche’s aphorism is a mere paradox, on which nothing can be built. Far more important was Marx, whose theory of ideology put power above truth as the motive of political thinking. The result of Marx’s theory was to suggest that my thinking is science, yours ideology: mine is the true voice of history, yours the ‘false consciousness’ of the bourgeoisie. Yet more destructive was Foucault, who rephrased the Marxist theory of bourgeois ideology in terms of the episteme of a culture — the fabric of concepts and arguments that the ruling class lays over society so that every voice speaks with its terms.

This was the dominant approach to the humanities in the 1970s and 1980s of the last century, and the way of thinking that has come recently to the surface in the apostles of the Momentum movement. It defined the position of the polytechnic left, who believed that ideas, beliefs and arguments are not to be judged in terms of their truth, but in terms of the ‘class’, ‘hegemony’ or ‘power structure’ that speaks through them. The question to be asked of every adversary was not ‘What are your arguments?’ but ‘Where are you speaking from?’ That, to me, was the beginning of the post-truth culture.

But this is where a bit of realism is needed. Politics is an opinion-forming and opinion-manipulating art. However much people can be influenced by slick advertising, mendacious promises and intoxicating slogans, they are influenced by these things only because the idea of truth lurks somewhere in the background of their consciousness. In the end we all respond to an inner ‘reality principle’, and will amend any belief when its refutation is staring us in the face. It is only someone buried in a social science department, lost in the turgid pages of Deleuze, Badiou and Habermas, who will go on believing that there is no truth, and therefore no real differences of opinion.

And that is why we should, when considering the Brexit vote, be guided by the truth of the matter. As d’Ancona insists, the debate was not conducted at the highest level, and there was a tendency on the Leave side to dismiss the assembled experts as merely experts, who didn’t count because they were assuming the existence of some fact of the matter. But we should recall the history of the EU, and how we became a part of it. We were invited to join a ‘customs union’, a ‘common market’, and nobody said that we were to surrender national sovereignty, to open our borders, and to submit to a new legal order that would dictate to us from a point outside the kingdom, regardless of Parliament and the Common Law. We were told a whopping great lie, not from a post-truth standpoint, but from the standpoint of politicians who seriously wished to deceive us, and seriously wished us to believe as true what they knew to be false. That was Sir Edward Heath’s great act of treason, and I blame him for it.

Of course it was wrong to ignore all those experts, who told us of the economic catastrophe that will ensue if we leave the EU, just as it was wrong of Mrs Thatcher to ignore those 364 economic experts who wrote to the Times in 1981 warning against the catastrophe that would ensue were her budget proposals to be adopted. (She did adopt them and by a miracle there was no catastrophe.) But that’s not the point. The troop of experts was to many voters simply a proof that the original lie persisted; the lie that membership of the EU is a trade agreement, a matter of mutual economic benefit, and nothing to do with our identity as a sovereign nation state. Whether or not you approve of referenda (and I don’t, any more than I approve of petitions on the web or political decisions broadcast by Twitter) it is clear that the Brexit vote was not about economics but about identity and that the people voted as they did in large part because Parliament had refused to discuss their principal concern over EU membership. This was not a post-truth response, but an appeal to the politicians to take truth seriously.

Of course, d’Ancona has a point. All plebiscites narrow the political process to a single question, and force us to think in terms of ‘yes’ and ‘no’, rather than ‘maybe’ or ‘yes, with qualifications’. We were not asked to consider the real solution to the sovereignty problem, which is to tear up that old treaty and replace it with another one, in which the national interests of all the signatories could be considered anew. And here, I suspect, we do encounter the thing that most troubles d’Ancona, which is the change to the human psyche brought about by social media, and the belief that you can decide even the most deep and difficult issues by a one-click response.