A few weeks ago, the University of Illinois at Urbana-Champaign rescinded its offer of tenure to a professor of English then working at Virginia Tech. Steven Salaita was offered a post as professor of American Indian studies, subject to the formality of confirmation by the university's board of trustees. Before the board met, the university's chancellor, Phyllis Wise, wrote to Salaita revoking the appointment: the board was, she said, unlikely to approve tenure, so the proposal to appoint would not be put to them. Since then, a large number of academics have signed petitions condemning UIUC's decision and undertaking to boycott the university.

Salaita had published tweets critical of Israel. Some of the tweets are certainly robust. Those to which UIUC seem to have taken exception include:

Zionists, take responsibility: if your dream of an ethnocratic Israel is worth the murder of children, just fucking own it already.

If Netanyahu appeared on TV with a necklace made from the teeth of Palestinian children, would anybody be surprised.

Only Israel can murder around 300 children in the span of a few weeks and insist that it is the victim.

Both Wise, who says that UIUC remains 'absolutely' committed to academic freedom, and the former American college lecturers' union president Cary Nelson, allege that Salaita's tweets were 'uncivil'. Nelson said he did 'not know of another search committee that had to confront a case where the subject matter of academic publications overlaps with a loathsome and foul-mouthed presence in social media'.

It's a good question what freedom of speech protects. Is it who gets to speak, what they say, or when or how they say it? Paul Robert Cohen was arrested in 1968 for wearing a jacket bearing the legend 'Fuck the draft'. He would presumably have avoided arrest had the jacket said 'I strongly disapprove of conscription'; but it's hard to believe that that makes the same political statement. The Supreme Court overturned the conviction, citing Cohen's first amendment rights. Content – what is said – should indeed get strong protection. But the very indissolubility of content and expression can be exploited by those who seek to marginalise views on the plea of etiquette. To insist that the content itself, as with the paraphrase of Cohen's slogan, can neutrally be inserted into public debate is to set oneself up as a custodian of meanings – as who can judge of synonymy, a move in a power game. Polysemy is always threatening to the authoritarian mind.

A lot of people, even some of my friends, routinely cuss on social media. Would Salaita, a Palestinian, have found himself in the same predicament had he been tweeting in similar terms about Hamas? Although a public university, UIUC depends heavily on private philanthropy, corporate donations and industrial contracts to top up its fee income. This may help explain the otherwise odd fact that a university, committed as Wise says to free intellectual inquiry, has decided that the first amendment needs to be tightened up.