The word 'fairness' is taking on greater and greater political duties by the day. It's logic was shattered months ago, and yet the government continues to pile additional weight onto it. I previously wrote that a conservative Rawlsian position was emerging, which treated existing forms of inequality as permanent, and merely in need of 'fair' treatment.

But it might be getting even weirder. I just heard Nick Clegg on the radio arguing that, whether or not he had previously opposed student tuition fees, his priority was now to ensure that the new policy was developed and applied 'fairly'. The word is now performing a very strange and rather troubling political role. Clegg is effectively saying that he inhabits some ethical future, in which policies that haven't even entered the House of Commons - never mind debated and voted on by our elected representatives - are part of the furniture, and his priority is to minimise their injustice.

This is political trolleyology. If a train were rushing down a hill towards a crowd of people, would it be right to push a fat man in front of it to block its path? Or to put it another way, if George Osborne were tearing up the British public sphere with no apparent concern for the consequences, would it be right to lend him a hand in the hope that he might be persuaded to do it more intelligently? Neither is a dilemma that any of us would like to find ourselves in. Perhaps if game theory was the reductivist psychological imaginary of choice for the Thatcher years, trolleyology will be the equivalent for the Coalition years.

Clegg's bizarre rhetorical strategy is made possible partly by one of the accidental legacies of New Labour. It's been noted that Cameron has adopted various Blairite political tropes - deliberately trying to annoy his own party in order to speak to the electorate, declaring how much pain his decisions are causing him (Clegg does this too). There's another one that I haven't seen reported, partly because it was never within Blair's control: implying that the guy in Number Eleven is a weirdo who can't be reasoned with.

The power-sharing that goes on between Number Ten and the Treasury is now working in the interests of both, to a much greater degree than it did under Blair. The split is actually Humean to the core. Clegg and Cameron represent fairness, decency and the common good; Osborne represents objectivity, facts and economics. The former want a better world, but know little of its reality. The latter knows about its reality, but doesn't care what happens to it. Osborne unleashes trolleys down hills, while the rest - and the Lib Dems in particular - are tasked with pulling leavers, pushing fat people off bridges and diving in front of the odd trolley themselves, all in the hope that this minimises the suffering.

The problem with this is not the quality of the deductive reasoning itself ("is this fair, given various presuppositions, or not?") but with granting such authority to abstract deductive reasoning in the first place. Like game theory, trolleyology forces one into a set of conclusions, on the basis of circumstances that do not currently exist. Likewise, Clegg is deducing his notion of fairness from a policy doesn't even yet exist, quite aside from whether it is a desirable or 'fair' one in itself. By converting a Conservative/Liberal Democrat policy - tuition fees will rise to £9,000 a year - to the status of some sort of assumed and unalterable premise, Clegg is pulling a fast one. It's a clever, brutal and disingenuous political strategy, which he shouldn't be allowed to get away with.