Boris Johnson will try to wriggle out of it, but he can’t escape blame for any future violence against MPs

Even if a perpetrator is fully responsible for what they do, it doesn’t follow that no one else should be blamed in addition. Johnson's language does genuinely risk inspiring unhinged listeners to engage in actual violence

“Surrender.” “Betrayal.” “Sabotage.” These words are now commonplace in our political lexicon. One-hundred and eighteen bishops have condemned the inflammatory language heard in the House of Commons over the past week. MPs excoriated the prime minister for his incendiary talk of “surrender”, invoking the role of dangerous speech in inciting the murder of Jo Cox.

But the prime minister was unmoved, dismissing the criticism as “humbug”. Jess Phillips MP fired back: “If one of us gets hurt, I’ll blame Boris Johnson.” But Johnson doubled-down, telling the BBC that his rhetoric was “entirely legitimate”.

Who is right? Our debate on Brexit is now engulfed in a meta-debate about how we discuss Brexit, and how we talk about politics generally. With so much to think about already, it is tempting to dismiss the meta-debate as precious hand-wringing, distracting us from more serious concerns. But that would be a mistake.

Words matter. Extreme rhetoric encourages us to think of those with whom we disagree as enemies to be vanquished, not fellow citizens to be engaged. That makes compromise less likely. It sows social division. And – most dangerously – it risks inspiring unhinged listeners to engage in actual violence.

Yet if words matter so much, why do so many dismiss this issue? It all comes down to some widely held but wrongheaded philosophical assumptions – about the relationship between speech, harm, and moral responsibility.

The first assumption is that when someone is inspired to do harm, the perpetrator alone is fully responsible – and so the blame lies with him alone. There is a grain of truth to this. If Criminal A came up with his plan all by himself, and Criminal B got the idea from a website, we don’t blame Criminal B less. Those who harm others are fully responsible for violating their duty not to harm others, regardless of who or what inspired them.

But even if a perpetrator is fully responsible for what they do, it doesn’t follow that no one else should be blamed in addition. Suppose I give you a gun, knowing you intend to use it to rob a bank teller. That doesn’t mean that only you are to blame when you use it to do so. I am rightly accountable, too. We are both fully to blame for violating distinct moral wrongs (you, the wrong of robbery, and me, the wrong of aiding and abetting robbery).

The underlying insight is that blame is not a fixed-sized pie that must be divided up. The more people are implicated in a wrong, the more blame there is to go around.

The second faulty assumption is that a speaker is only blameworthy for inspiring violence if they does so intentionally. The prime minister, let’s assume, does not intend to cause anyone in his audience to attack anybody. That fact is relevant to our assessment of his character – he is better than someone who does intend to inspire violence. But it is morally irrelevant to our assessment of his actions. It is fully possible to incite violence recklessly or negligently; it need not be intentional to be wrong.

Perhaps we think it wrong to legally punish unintentionally dangerous speech. This is the view embedded in American law – though it is striking that the UK’s ban on stirring up racial hatred does not require intention, nor does the ban on inciting terrorism. What sort of dangerous speech ought to be banned is a difficult question – one I have studied in my research. But we can disagree about that fraught question while recognising the principle relevant for today’s debate about Johnson: to be morally blameworthy for inciting violence, and so appropriately subject to criticism, one need not intend to do so.

The third faulty assumption is that a speaker is only morally blameworthy for inspiring violence if violence actually occurs, or at least if it occurs soon enough that a simple causal connection can be established. But this, too, isn’t true. Casting fellow citizens as villains in our midst is wrong not because it will necessarily inspire violence, but because it risks inspiring violence.

Consider: speeding in a car is wrong not because you will necessarily hit someone, but because you risk doing so. Similarly, incendiary speech is wrong because it runs an unacceptable risk of inspiring violence – and for no good reason.

Thankfully, the public is starting to appreciate that words matter. In a new survey released by YouGov, 75 per cent of British adults said that it matters what type of language politicians use. Sixty-three per cent indicated that they thought the tone of politics today is “too aggressive” – a sentiment expressed by Remainers and Leavers alike. But these numbers are still too low. We should strive to make it common sense in our culture that words shape attitudes, and in doing, influence what people do. We are therefore responsible for what we say, no matter our intent, in light of how it risks affecting others – for good, and for ill. The prime minister should take note.

Jeffrey Howard is a lecturer in Political Theory at University College London