Jeremy Corbyn has been the victim of performativity.

A performative statement is one which doesn't describe reality but rather creates it - as, for example, when a priest says "I pronounce you man and wife."

Calling Corbyn "unelectable" is like that - it's performative. If enough Labour MPs say he is unelectable, then he becomes so because he looks like a weak leader. To see this, imagine that all Labour MPs had declared that Corbyn were doing a great job. The party would then seem united and so be more popular.

In this sense, when John McTernan accuses Corbynistas of refusing to compromise with reality, he is right in the same way that a man who kills his parents is right to plead that he is an orphan.

I don't say this to complain. I do so instead to suggest that performativity is more common than we might think. Take three very different examples

- As the wonderful Donald MacKenzie has pointed out (pdf), the statement "markets are efficient" created a reality in which index-tracker funds were launched.

- Priming and stereotype threat can create the behaviour they describe: if women are primed to act "feminine", they will do so. Judith Butler's language might not be to everyone's taste, but she's got a point.

- Brexiteers claim that leaving the EU would save £350m a week was a barefaced lie. But in helping Vote Leave to win the referendum, it has led to an abandonment of Osborne's austerity policies which might in fact allow for increased spending on the NHS.

In fact, I suspect that one of the biggest clichés of recent years embodies two other examples of performativity - that the left won the culture war whilst the right won the economic war.

The left did so in part by banishing "unPC" speech (that is, bad manners) and thus helping to equalize - to some extent - gays, women and ethnic minorities. The right also did so by the use of language. For example, the statement that people are entitled to their own money leads to lower tax morale which shifts the Laffer curve against high tax rates. And the language of bosses as risk-takers encourages a misplaced deference to them.

My point here is perhaps a trivial one - that language helps to create reality. The problem is that, for the most part, the right has had more power and ability to do this than the left.