It’s been an eventful week for what we used to call truth. The Saudi government has finally admitted that Jamal Khashoggi has been killed, although its account of how this happened is as implausible as the various denials it supplants. That we rely on Recep Tayyip Erdoğan, the world’s most enthusiastic jailer of journalists, to help establish the facts is one of the ironies of a post-truth world.

Talk about the demise of truth is always liable to sound histrionic and naive. After all, we have long been told that the prince must be “a great feigner and dissembler” (this is Machiavelli, not the House of Saud), and “realists” ever since have stressed the usefulness of illusions and the necessity of lies. Indeed, recent research by Ezra Zuckerman Sivan indicates that a large constituency of voters expect their political heroes to lie on their behalf.

Politics, for the hard nosed, is about power and it may be unrealistic to think that it can be made subordinate to other ends, such as truth. It is also easy to ignore how the pursuit of truth can breed a fundamentalism of its own, a point made by Edmund Burke during the French Revolution. The “philosophical fanatics” of France, he maintained, prioritised abstract truths about justice over civility and mutual convenience, with disastrous consequences for everyone.

Similar claims were made about the Bolsheviks in the 20th century. Returning from a visit to the USSR in 1920, Bertrand Russell proclaimed that it was dangerous to use politics to sponsor expansive schemes of truth (such as dialectical materialism): since truth is generally held to be binding for all times and places and peoples, such a politics will quickly assume an aggressively imperialistic form.

Nonetheless, it’s easy to feel worried that truth’s empire is in decline. George Orwell was one of truth’s Cassandras, but he tended to relate the rise of authoritarianism not to a dogmatic objectivity, but to the advance of relativism. Nazis were the worst sinners: “Nazi theory specifically denies that such a thing as ‘the truth’ exists. There is no such thing as ‘science’. There is only ‘German science’, ‘Jewish science’ etc.”

Incoherent as it may be, Orwell worried that relativism was fed by the great “modern disease” of nationalism and the subdivision of the world into discrete and hostile units. “Indifference to objective truth,” he complained, “is encouraged by the sealing-off of one part of the world from another.”

Despite China’s best efforts, this type of isolation is hard to effect in an internet age. Yet as we have seen, the fragmentation of news sources and the rise of social media have produced new forms of collective solipsism in which lies are circulated with alarming speed. Often in these contexts, truth is neither the goal nor horizon of political debate: it is simply the metaphor chosen to exalt one’s prejudices and to crush one’s opponent. Or, as Orwell put it, truth “becomes untruth when your enemy utters it”.

Orwell insisted it was a sentimental illusion to assume that “truth will prevail”. Nineteen Eighty-Four (1949) gives a boot in the face to this kind of optimism. So does 2018. Nonetheless, in these dark times, it’s worth recalling Winston Smith’s famous line: “Freedom is the freedom to say that two plus two make four. If that is granted, all else follows.”

The key thing here, some argue, is that we should be free to say our sums, not that they should be correct. But this seems to miss Orwell’s point. Free speech is important but it is not enough; as the trolls and the cyber-thugs reveal each day, freedom of expression is a dangerous licence when it is severed from any commitment to truth. Such freedom erodes freedom itself, undermining our ability to account for ourselves and to hold others to account.

Orwell was wrong about many things, but he was right to suggest that a world that turns its back upon truth also gives two fingers to freedom. But how we should legislate for this fact is no clear matter. The Saudi regime has just warned its citizens that the circulation of “fake news” is a criminal offence. With friends like this, truth no longer needs enemies.

• David Dwan is the author of Liberty, Equality & Humbug: Orwell’s Political Ideals and is associate professor in English at Oxford University