FREEDOM of speech is not a given: it has to be fought for. Always there will be those who want to silence people they dislike or disagree with. And – always – those of us who consider this wrongheaded and, indeed, dangerous, must fight back.

None of this is new, but all of it remains vital. John Milton knew it when he penned his great tirade against censorship in 1644. Voltaire knew it when he battled the censoriousness of the church a century later. And John Stuart Mill knew it when he wrote the most brilliant, and the most impassioned, defence of free speech of them all.

Mill’s genius was to put his finger on the core of the problem: speech cannot be banned just because someone is offended by what is said. It can be banned only when it causes harm – and being harmed is not even remotely the same as being offended.

None of this means that speech can go unregulated. “Free” speech is, and always has been, something of a misnomer. We may not use words to harm one another – that is to say, to threaten or to abuse one another. Similarly, we may not use words to defame one another. Threatening speech may be criminal. Defamatory speech may be actionable.

To be even the strongest advocate of free speech, then, is in no sense to imagine that speech can go unlicensed, still less that there should never be consequences attached to what you choose to say. But it is to say, with Mill, that causing offence is, of itself, never a sufficient reason to cancel someone’s speech. If you are offended by something someone has said, the answer is not to silence them, but to speak back.

Freedom of speech is in the news this week because of two incidents: the attempted murder of Sir Salman Rushdie in New York, and the cancelling of Jerry Sadowitz’s show at the Edinburgh Fringe. It will be for the American criminal justice system to determine the motives of Rushdie’s attacker but Sir Salman’s life has been under threat for 30 years because what he wrote in one of his novels offended followers of one of the world’s great religions. I read The Satanic Verses when it was published – it is a brilliant novel. I lent my copy to a friend and never saw it again. I ordered a new copy this week and will re-read it as soon as it arrives.

I’ve never been to a Jerry Sadowitz show. I’m not much interested in conjuring tricks and his brand of humour does not appeal to me. If you are a theatre manager booking Sadowitz, or if you are a punter buying a ticket, you surely know what you are letting yourself in for, even without all the trigger warnings plastered on the announcements advertising his show.

No one has to read a Rushdie book. No one has to go see a Sadowitz show. To want to live in a world where Rushdie books are available to read and where people are free to attend a Sadowitz show if they wish is not remotely to agree with – still less to approve of – everything Rushdie has written or everything Sadowitz says on stage.

But that’s the whole point of free speech. We should, each of us, be free to choose what books we read, what shows we attend, what films we watch. We should, each of us, be free to make these choices for ourselves.

This freedom cannot be taken for granted: it has to be fought for. For there will always be those who think they know better, and who would like to choose for you. Sometimes it is the state – the Iranian state in the case of Rushdie but, not so very long ago, the British state in the case of other novelists (DH Lawrence, anyone?) More often in today’s world, however, it is not the state at all, but other self-appointed guardians who have taken it upon themselves to police the boundaries of what we may say, or hear, or write.

When Maya Forstater tweeted her view that sex is immutable and that men cannot transition to become women she found that her employment with a thinktank, the Centre for Global Development, was terminated. When Allison Bailey, a barrister at Garden Court Chambers, queried her chambers’ involvement with Stonewall’s diversity and inclusion campaign, she found herself victimised. When Harry Miller tweeted his gender critical views, he found the police at his door and was told by an officer that they needed “to check his thinking”.

Maya Forstater, Allison Bailey and Harry Miller each won their case in court, the judges ruling that their employers (in the first two cases) and the police (in Miller’s case) acted unlawfully. These cases are important – for they are reminders that free speech is not just for superstar novelists or controversy-courting comedians. It is for all of us.

Of course there are big differences between Rushdie, Sadowitz, Forstater, Bailey and Miller. But there is also a single common thread that binds them together. In each case their speech caused offence. And, in each case, instead of arguing back, somebody somewhere decided that the right thing to do was to silence them, to cancel them, or to persecute them. In each case, that was both wrongheaded and dangerous.

“May your pen be unbridled”, wrote John Milton in 1644. “May you be a perpetual reader of … books unchosen” for you by the powerful or the self-appointed police officers of conformity. You don’t have to agree, of course. But don’t cancel what you disagree with: engage, argue back, speak up, and speak out. Have the courage of your convictions. Unbridle your pen.