Writers don't like repeating words, so it's always good to have a synonym at hand. Back in the 1980s, when I first started writing about politics, I would call the SDP-Liberal Alliance, on second mention, "the centre party". The two were as interchangeable as "Conservative" and "Tory". Then John Major took his party to the left and Tony Blair drove his to the right and the Liberal Democrats were squeezed so hard they could barely breathe.
Blair was so determined to occupy the centre ground that the Lib Dems couldn't find a toehold. No wonder they were tempted to outflank New Labour to the left. No wonder it became increasingly hard for political journalists to describe the Lib Dems as "the centre party".
But the as-yet-untold story of British politics at the moment is that space has opened up again in the centre – for the first time in two decades – and that the Lib Dems are in the best place to fill it. Yesterday, Danny Alexander quoted his predecessor as Highlands Liberal MP, Russell Johnston: "Liberal positioning in politics is like the nose in relation to the rest of the face: somewhere in the middle and out in front."
The "out in front" has always been one of the most attractive elements of the Lib Dems. Policies for which they were once derided, such as gay marriage, are now becoming part of mainstream political debate. So will legalisation of cannabis one day. The Daily Mail may scoff, but the Lib Dems' willingness to break taboos, to be in the vanguard, is a healthy part of our otherwise sclerotic political culture.
The "somewhere in the middle" part matters more, though. It is critical both to the Lib Dems' electoral success and its ability to form coalitions when the electorate delivers a hung parliament.
Ask most voters where they sit on the political spectrum, and the most popular spot is very close to the centre. That was the foundation of Blair's election-winning genius: he positioned himself – and tried to position his party – as close to the average voter as he could.
Nick Clegg, in his speech on Wednesday, is going to say that his is the only party that can now deliver both economic competence and fairness. Remind you of anyone? Blair was always going on about marrying economic efficiency and social justice. He knew that voters would never elect a Labour government unless they could trust it to run the economy. But they were concerned about the effect of Tory policies on the poor. A party that could offer both economic efficiency and social justice would hit the electoral spot.
So how has Clegg suddenly found himself in possession of this sweet spot? It's one part application and one part luck. He has shown that he is prepared to sign up for tough decisions on the economy, and his party has shown a surprising willingness in government to stand by those decisions. Clegg has also positioned the Lib Dems as supporters of public-service reform, on the side of pupils, parents and patients rather than teaching or health unions.
His luck is that the other two parties have made room for him. Ed Miliband has moved Labour to the left. It is no longer trusted to run the economy competently. Voters still blame Labour for the economic mess that the Coalition inherited and they have more faith in the Coalition's remedy. Obviously this helps George Osborne more than Clegg, but if the Government's medicine works, the Lib Dems will be able to claim some credit at election time.
Miliband has also made space for the Lib Dems on public-service reform. Labour's opposition to free schools and its ambivalence about academies (introduced by Blair) mark a big step back from the centre ground. The Lib Dems aren't in hock to the public-sector unions or any other vested interests and Clegg's instinct is to shake up public services when they're not delivering.
Meanwhile, both Cameron and the right of his party are making even more room for the Lib Dems. Nadine Dorries's question to Cameron last week about why the centre party – see? I did it – wielded so much influence with so few seats could have been drafted by Clegg's spin doctor. Every time the Tory right complain about Lib Dems protecting human rights or preventing them cutting the 50p tax rate, the smaller party looks more centrist.
Cameron too has bolstered the Lib Dems' claim to the middle ground. He has allowed them to take credit for almost every civilising amendment to Tory policy, whether it is watering down the badly-conceived NHS reforms, introducing the pupil premium or raising the income tax threshold. This may help his relations with the right – "It was the Lib Dems who made me do it" – disguising his delight that the centre party has given him cover for changes he would happily have made himself. In the longer term, though, it damages his own positioning. Voters will see him as a right-winger dragged reluctantly to the centre by his Lib Dem partners.
So why is none of this showing up in the polls? Yesterday's made depressing reading for the Lib Dems. In the YouGov/Sunday Times poll, 48 per cent of voters thought the Lib Dems were wrong to go into the Coalition and 36 per cent that they have permanently damaged their party by joining it.
But changing public perceptions takes time – a lot of it. Most people aren't remotely interested in politics between elections and messages have to be repeated countless times before they are heard. It is encouraging for Clegg that the same poll found that since May, the proportion of people thinking the Lib Dems had a lot of influence in government had doubled (admittedly from a low base). Moreover, 23 per cent think they will recover in time for the next election and 21 per cent that they will benefit from having been in government.
There was always going to be pain before there was any gain. Once Clegg went into coalition with the Tories, he was instantly going to lose the protest voters and the more-left-wing-than-Labour voters. When he went back on his pledge to abolish tuition fees, he was bound to lose most of the youth vote. It's just like when you're trying to sort out a very untidy child's room, and you have piles of stuff all over the floor: it looks worse before it looks better.
Clegg still has nearly four years, though, to reclaim the centre ground for his party, four years in which he can make that attractive pitch for economic efficiency twinned with social justice, bolstered by experience of governing. Lib Dems feared that they would lose their identity in government. In reality, they have a great chance to re-establish it – as the electoral heirs to Blair.