One of the more irritating memes of the Labour leadership election has been the use of the word "credible". For example, Gordon Brown says "the best way of realising our high ideals is to show that we have an alternative in government that is credible." Yvette Cooper says: "We have to have a radical alternative and it also has to be credible and Jeremy's approach isn't." And Andy Burnham says Corbyn's plans "lack financial and economic credibility."

I don't like this word "credibility" because it's horribly ambiguous. It can mean four things.

First is a technical meaning: policies are "credible" if they are time-consistent. Tony Yates' objection to Corbynomics is along these lines - that in undermining Bank independence it could raise future inflation. But I'm not sure most uses of the word have this meaning.

Secondly, it could simply mean "vague". Burnham seems to have this in mind when he complains that Corbyn hasn't spelled out how to pay for free university education or nationalization. ("We'll borrow" is of course one possible and reasonable answer.)

Thirdly, it could be just a pompous sounding word for "bad" - an attempt to dress up a value judgment in apparently technocratic language. My problem with this is that it elides a crucial distinction - between policies that are unpopular and ones that would have adverse effects if implemented. The distinction matters enormously because many good policies are unpopular (eg liberal immigration, basic income, land taxes) and bad ones popular (eg deficit fetishism, benefit cuts).

The fourth possible meaning is, however, the nastiest. I fear that "credible" is often used to mean "unacceptable to the Westminster-media Bubble".

The problem with this is that the Bubble is detached from reality: it believes unthinkingly in deficit fetishism; over-estimates median incomes; and stigmatizes welfare as a cost rather than seeing it as reasonable insurance, for example. Talk of "credibility" thus means surrendering to economic illiteracy - which can hardly be the basis of good policy.

Now, I don't say all this to endorse Corbynomics. There are reasonable objections to it - not least of which is that, with real interest rates negative, there's simply no need to print money. All I'm saying is that Corbyn's opponents should not hide behind pseudo-technocratic talk of "credibility".