Ian Bell reviews two important books ahead of the independence referendum.

David Torrance - The Battle For Britain: Scotland And The Independence Referendum, Biteback, £14.99

Stephen Maxwell - The Case For Left Wing Nationalism, Luath Press, £9.99

Those determined to preserve the United Kingdom have been testing a new piece of rhetoric. It seems several of them thought of this one simultaneously. The 306-year-old arrangement between Scotland and England is, they say, "the most successful political, economic and social union the world has ever known".

The fact that the claim is a touch sketchy doesn't make it wrong. It is possible that in the entire history of the entire planet we alone have found a winner. If that's the case, it invites a question: why do so many in Scotland fail to recognise this astounding truth? To put it another way: why, after three centuries, are the Scots still at it? If the grand boast describes a remarkable fact, why are we not contentedly assimilated? It's been a while. We should have settled for costumes, quaint grub and fit-for-tourists history long since. Why not?

The question has all but disappeared from the independence argument. This might be because it involves the persistence of identity and because that's a topic the parties don't want to touch. It's too complicated. Before you know it, someone will be asking still harder questions. Here's one: what is nationalism, exactly?

It's odd that amid a brawl over the consequences of the phenomenon so few ask about the phenomenon's nature. There is no shortage of useless snap definitions. Plenty of Unionists will give the lecture on atavism, populism and "racism", while the SNP heads in the other "civic" direction, mentioning - as Nicola Sturgeon has done - that identity isn't relevant. But of clarity there is none.

In one sense, that's understandable. Political science has struggled with nationalism. Historians have laboured to join the dots between dates and countries. Politicians, at least among the semi-democrats, have acquired the habit of dismissing everyone's nationalism save their own as divisive and dangerous. The problem isn't hard to state: some things done in the name of the nation have been hideous, some magnificent, some risible.

David Torrance does a service, then, when he records that the SNP's nationalism has altered radically since the party's founding in 1934. Stephen Maxwell's posthumous collection is equally valuable in its efforts to claim - to reclaim - nationalism for the left. In one sense, volumes by authors who would not otherwise have had much in common draw together over the issue of identity, of Scotland's sense of itself, and how this has shaped attitudes.

Torrance is plainly right in his description of the SNP's evolution. Some sections of the party might cling to the old, sentimental tartanry and the belief that liberation from the yoke - you'll know which yoke - is all Scotland could ever require. Alex Salmond and his civic society technocrats, egalitarians with a taste for conservative economics, have no interest in that. They wear it, if at all, for Sunday best, not the working week.

It is no more a criticism of the SNP to say so than it is to ask what part of "Labour Party" still applies to Ed Miliband. Nevertheless, the manner in which Mr Salmond has shaped the party that once kicked him out - for his role in the "socialist" 79 Group - is central to Torrance's carefully-told story. The SNP is no one-man band, but the orchestra has one conductor.

A second strand has to do with Mr Salmond's success. Once upon a time, the SNP would have regarded a majority at Holyrood as a mandate for independence. Instead, guided by its leader, the party has sought and won parliamentary power, general approval and a referendum. Yet somehow it cannot seem to turn support for its work in government into consent for independence. Too few SNP voters support the SNP.

Part of Torrance's narrative of the journey towards the referendum is built around this fact. Artfully he gives it context. What is independence in a globalised world? What sort of autonomy counts when a small country regards a British Union entwined with a European Union? Sovereignty is a compromised word. Torrance adapts William McIlvanney's image of the Scottish lion, "feart" in 1979, a cub again in 1999, as it paces an enlarged cage, troubled by the illusion of freedom.

Maxwell's book, a collection of essays and articles, is a different kind of exercise, yet animated, on its readers' behalf, by the same fundamental questions. What is liberty and where does it lie for the mass of people? Since Maxwell was one of the first of his generation to tackle what was held to be a conundrum for the left - nationalism opposed "by definition" to internationalism, they said and say - he spoke both to a divided polity and to the notion of identity.

Maxwell's son Jamie recalls that his father hesitated over the idea that "a nation should be independent simply because it is a nation". The most subtle of SNP thinkers wanted more: sovereignty for the sake of change, sovereignty as a progressive idea. Long before it was fashionable, Maxwell was interrogating the hope that Scotland is a nation found always on the maps of the centre-left. Class mattered and matters.

Torrance makes too little of this; his opponents would say Maxwell made too much. But there is fair-to-good evidence that the rigged referendum of 1979 was approved by the old working class and opposed by Scotland's middle class. There is polling evidence now that a Yes vote is a more appealing proposition in housing schemes than it is among professional types. To the question "Whose Scotland?" comes the answering question "Whose identity?"

These are two among numerous books published or about to be published on what should still be called the question of Scotland. Torrance is an elegant writer and a fine reporter on the tidal shifts of politics, but his narrative finds room for the ideas that have brought us to where we are, the place and the moment predicted by no one just a few years ago. In contrast, Maxwell is, refreshingly, all ideas. Some of those, first aired in the 1970s and 1980s, still resonate. They might remind a few folk that self-determination is not as novel as they think.

In his essays and articles Maxwell was driven by the belief that Scotland's need for independence matters as much, if not more, than its right to independence. Torrance reports, meanwhile, from a country susceptible to fear and its project managers. But the latter also attempts the bold experiment of imagining a Yes vote: our oil (and fund), our EU membership (while rUK withdraws), our currency, demographic pressures, the Sturgeon succession, Labour's return to power.

It's fascinating. Doom is absent but liberty is circumscribed. Ironically, Maxwell also reaches his last printed words by counselling the left to be patient. Independence, he warns, is "unlikely to spark an instant Scottish Spring of radical reform". It seems this is a country still held in balance by its contradictions. Perhaps it needs a referendum and a dunt.