"Everyone takes the limits of his own vision for the limits of the world," wrote Schopenhauer. For Gladstone, echoing his mentor Robert Peel in a celebrated parliamentary speech, the challenge facing his colleagues - if they were ever to renew and remake the party and the nation - was to "elevate your vision", to dare to go beyond what was familiar and comfortable.
The limits of vision or the absence of it: so far, the five candidates competing to become the next leader of the Labour Party have been accused of lacking what can be called the "vision thing". In a recent issue of this magazine, they were caricatured as five politicians in search of a big idea - in search of something, anything, to galvanise this slumberous, summer-long campaign. Commentators have written of the desultory nature of the contest, as the candidates travel around the country addressing one dreary hustings after another: a slow-moving convoy of repetition, the sound of a party speaking only to itself.
According to Roy Hattersley, deputy leader of the Labour Party from 1983 to 1992, the process is much too insular. "Too much time has been spent fighting the battles of the past and talking about the cuts," he tells me. "The candidates need to start saying: 'Listen, this is what I would do if I became leader.' They need to start speaking about what they would do in new circumstances in the future, not what they would have done in the past or what they would be doing now in opposition to the Conservatives."
The former chancellor Alistair Darling agrees. "For me, David Miliband is clearly the strongest candidate," he tells me, "but I still want to hear him and the others reaching out to address the country. That is what Tony [Blair] did so successfully in 1994." My own impression, having chaired the New Statesman hustings on 9 June, the first official event of the contest, is that there is no shortage of desire or intellectual energy among the candidates. The challenge after their years in power - if you exclude the career maverick Diane Abbott - is for each man to find an authentic voice as he emerges from his protective ministerial cocoon and starts to reveal more of his true character and values.
Midway through the contest, each has a settled persona. David Miliband is the prime-minister-in-waiting, the long-time favourite, prepared to defend the successes of the New Labour years while seeking to strike out in daring, new directions. His brother, Ed, is the insurgent, the figure most attractive to young activists in and around the party, as well as those who long to transcend the old factionalism of the Blair-Brown feud, the detritus of which is once more being excavated by the Mandelson memoir. Ed Balls is emerging as the fighter, a natural opposition politician, a ferocious antagonist and opponent of the coalition and, especially, of its doctrinaire deficit reduction programme. Andy Burnham is the outsider, the candidate keenest to position himself as the embodiment of working-class aspiration. Abbott remains as she ever was: a voice from the often-neglected hard left of the party.
Yet the campaign with the most momentum is Ed Miliband's. After equivocating for a long time over whether to run for the leadership against his brother - the former foreign secretary, who was preparing to stand long before the May election - the 40-year-old MP for Doncaster North and former secretary of state for energy and climate change has campaigned with vitality and discipline. When I visit him one afternoon at his office in Westminster, he repeatedly refers to himself as the change candidate, a predictable formulation: nobody seeking to win a leadership contest is going to describe himself as the candidate of reaction or the status quo, not when his party has lost an election with only 29 per cent of the vote.
“My message is clear and gaining support," Miliband says, drinking a cappuccino from a paper cup, photocopied pages of the newspaper extracts of Peter Mandelson's The Third Man scattered on the small table in front of him, "and that is: I am the most credible candidate of change and this is a change election for Labour. I've been honest about where we went wrong. Iraq was a mistake, I've said that. The state was too overbearing in relation to civil liberties under Labour, I've said that. We left an economy that was good at creating jobs but left more people working harder and longer for less money. We let markets become too powerful in our society. Unless we have a leader who recognises the scale of that challenge, we won't win."
He says he is both the head and the heart candidate. "People say I'm the heart candidate because I have passion and values but don't have
a story of how to win. David is the head candidate, because he's all strategy and positioning. But that's wrong, because I'm the head and the heart candidate. I have a story of how to win.
“First, we misinterpret New Labour at our peril if we think it was just about occupying the centre ground. It was about having a clear sense of values - we were the party of the windfall tax and the minimum wage, after all. Unfortunately, we became the party of defending bankers' bonuses and ID cards.
“Second, we must recognise that New Labour got stuck in its own orthodoxies on the economy, the banks, civil liberties and foreign policy. I can reach out to the liberal voters who left us over Iraq and civil liberties."
He pauses and then digresses to say that he supports the coalition's proposed civil liberties reforms. "I agree with what they have done on reviewing Section 44 of the Terrorism Act, because it's right to say that what started out as a narrowly constrained power around terrorism has been used very widely. I'm not going to disagree with the government for the sake it. On crime, for instance, Ken Clarke is opening up the debate and I agree with that."
To supporters of Ed Miliband, such as Alex Smith, editor of the website LabourList, who was approached before the election to work on David's campaign, their man is challenging the establishment as represented by the former foreign secretary, whose campaign has attracted the largest donations and the support of most of the shadow cabinet. "I was in the US for the Obama campaign in 2008 and I can see similarities between that and this campaign. David is the establishment. He is more tainted by the perceived failures of the Labour government. He has a problem of empathy, too. He comes over to some people as superior and snippy, as someone who looks through or over people. And Ed has so many strengths. There is a passionate grass-roots contest in his favour. Ed is the grass-roots candidate with a campaign that's only just coming together, but at the right time. He is fresh and honest, with a powerful core message of values and of not repeating the New Labour playbook. To the public, he's a blank canvas. That's exciting."
Speak to those who have known Miliband since his Oxford days and they will say largely the same thing: he's nice, decent and charismatic. But they are not sure what he stands for beyond the wish to create a fairer society and to redistribute more. Nor do they think he would be able to challenge the party and to turn it into a winning force once more. "I think the interesting thing is it's only now, during the contest, that people are starting to see a steel in Ed that few realised was there," says a close friend. "He's being pretty ruthless in attacking his brother, but subtly. Also, the format of the contest plays to his strengths, because live audiences really respond to him. If you go to the hustings [you'll see] the difference - when Ed gets up and makes his presentation, it lifts the room. David doesn't have that. It's partly the message, too. David is challenging the party in that classic Blairite way: that they mustn't retreat to their comfort zone. I think he's right, but I think, perhaps, Labour members have had enough of that for the moment and Ed's more core-Labour message is going down better."
“I've always been clear about my values," Miliband says when I put some of this to him. "I care about inequality; the gap between rich and poor scars our society. We have to drive through a living wage and do something about top pay, such as having a high-pay commission. The problem is we stopped talking about this issue of the top. I don't think Tony Blair was right about the gap [between rich and poor]. To give up on doing anything about it before you have even tried - that's wrong.
“We went from making our peace with capitalism to saying we can't criticise capitalism or markets. I'm a socialist because I'm a critic of the injustices that capitalism throws up. I want a fairer, more just, more equal and more sustainable capitalism than we have. We need a more responsive state and a less overbearing state as well. We didn't rethink enough after the credit crunch. It was a progressive moment and we didn't seize it. Why? I think it's hard to renew in office. You get stuck in your own orthodoxies."
All of this plays well with the left of the party, but there is scepticism. "I think Ed is in a comfort zone," says one former minister. "He's telling the party what it wants to hear on inequality and the rich. It's a good tactic. But it's not rooted enough in the real world. Where's the plan for reaching out to those people who voted Labour for the first time in 1997 and have since turned away from the party? I want a leader who can talk to the whole country, including those who read the Daily Mail. I think David [Miliband] gets it.
“I, for one, believe that Gordon was bonkers, for want of a better word, even though he gave me a great job. Ed chose to work closely with him for 15 years. That puts a question mark against him. For me, he's the geeky one, not David. I don't trust his judgement. But he's nice."
Miliband counters: "I'm pleased people think I'm nice. My personality is of someone who gets on with people. I hope I can be a unifier. Whoever is leader has to work with all the talents we have. No more Blairites, no more Brownites."
What of the charge that he is tainted through his close association with Brown? "I'm very close to Gordon and I admire many things about him, but ultimately I am most of all a Labour person. On Gordon, I'm instinctively loyal. I'm not going to spend this leadership campaign slagging off Gordon or, indeed, Tony. But if we put this defeat down to Gordon, I think we profoundly misunderstand the real issues we face about whether Labour was telling people a convincing story about their lives. We all bear a responsibility for that.
“The minute this leadership contest is over, the past is another country, as far as I'm concerned, no matter what has been said. If I don't win, I'd happily slot into a shadow cabinet. If people say bad things about me, things they will regret, well, that's what happens."
There has been a slight darkening of mood as the campaign and the rivalry between the brothers intensify: the briefings are not poisonous, but they are persistent. The brothers' relationship has been affected. "How can it not be?" says someone close to David. "He's shown enormous forbearance over this annoying younger brother." Other David supporters are saying that he will leave politics altogether if he loses the contest and Ed becomes leader, and yet this is something he denies in his interview with Mehdi Hasan (see facing page).
The brothers' relationship is complex. Throughout his life, David has needed only to glance over his shoulder to find Ed shadowing him, a few purposeful strides behind. Ed followed David to Oxford, where they both read philosophy, politics and economics; he then, like his brother before him, became a Labour Party strategist and policy adviser. Like his brother, he became an MP and cabinet minister, and now, here they are both running for the leadership, David having declared first. "David did the right thing to say that he would not stand in my way," Ed says now. "I told him face to face at his house that I was standing and he said, 'Look, I won't stand in your way.' I very much respect that. This is not some Shakespearean psychodrama, and, compared to Blair and Brown, we have handled it pretty well over the first months of this campaign. We are not making a big issue of it. I would serve under him if he won. Definitely. I have the toughness of someone who knows what they believe. That's the most important thing you can have in politics."
Hattersley, who calls Ed Miliband a modern Croslandite, because he is a libertarian and believes it is the obligation of the state not to impose equality, but to promote it, says it would be "a tragedy if David left politics, but you can understand it if he did. For a long time, it has been widely expected that he would be the next leader. Had he challenged Gordon, he would have won the leadership. Now he is being challenged by his younger brother. Was Ed right to stand against him? Of course. It was a function of his conviction to stand.
“Ed is much more genuinely progressive than his brother. Also, he is much more human. He has much more chance of connecting with the electorate. David is a very clever man. He looks like a very clever man. And when he communicates, he comes across as a very clever man talking to people who aren't as clever as he is. We'd have a much better chance of winning an election if Ed was leader. He'd be much tougher on the Tories. The Labour Party spent 13 years ashamed of being Labour. Ed is not ashamed of being Labour."
For the free-thinking Jon Cruddas, MP for Dagenham and a politician whom many on the pluralist left would like to have been a leadership contender, the candidates are only now beginning to find their range. "I think the contest has started to become more interesting in the last week or so," he told me. "I like some of the things David Miliband has been saying. I liked his Keir Hardie Lecture, because of its sentiment - it went deeper than simply policy. I liked the column he wrote in the New Statesman about England. He's interested in something deeper, in virtues."
Cruddas has spoken to me in the past of how Labour in power lost its language and became both hollowed out and compromised. The self-inflicted wounds of the Blair-Brown years - the culture of pernicious briefings, the top-down control-and-command edicts, the illegal wars, the Faustian pact with the forces of finance - are still open and festering.
Writing in the New Statesman in the immediate aftermath of the general election, Vernon Bogdanor, a former tutor of David Cameron, said that the coalition between the Tories and Liberal Democrats had ended the longed-for pluralist project of realignment on the centre-left and was a catastrophe for Labour, which was facing a generation in the wilderness.
Ed Miliband is more hopeful. "I think we can come back. The tragedy of this government is that it offers no story about future wealth creation or fair distribution of wealth or income. All it offers is a story about the deficit which ignores and overturns the lessons of the 1930s. You can't have the debate about the deficit in isolation from the debate about the spending cuts. I'm afraid we, Labour, played into that."
He is appalled by the Lib Dem surrender to the Tories. "I don't think we're being too hard on the Liberals. They're harsh on themselves. They've sold their supporters down the Swanee. They are a disgrace to the traditions of liberalism. It's no good Chris Huhne lecturing me in the Commons on what they are doing as being consistent with Keynes when he knows full well that their economic policies are a total betrayal of Keynes and he would be turning in his grave. I can see the death of the Liberal party, to be honest. It's quite possible they will split."
As I prepare to leave, Miliband says: "Look, Jason, I never thought I'd be in this position. I never thought about the leadership until after the election. But I think I have something distinctively optimistic to say about what progressive politics can achieve. I'm not the candidate of the easy life. The easier thing to do is to say the gap between rich and poor is always going to be with us. The harder path is to say we need to do something about it."
But does he have an overarching vision of change? I remind him of that line from Margaret Thatcher as she launched her counter-revolution. "Economics," she declared, "are the method, but the object is to change the soul."
Does he have similar ideological conviction? Does he have the stamina for the long struggle?
“Yes, I do. I'm not going to give you lots of policies, but we have to find ways of making our tax system more progressive. Unless you convince people that tax is the price we pay for the good society, and not simply a burden, progressive politics is always going to struggle. New Labour defined itself by attacking Old Labour.
I think you should say what you want to change about the country rather than what you want to change about the party. That's why I'm saying in this campaign what I believe. People can decide whether they want me or not."
If you weren't a politician, what would you be?
An actor. No, I wouldn't be a very good actor. Maybe an academic.
What's your favourite meal?
Chinese food, like Cliff Barnes in Dallas. I was a fantastic Dallas fan.
What does God mean to you?
God is something that some people believe in, and I don't.
Have you ever taken drugs?
No. Sorry. I'm so boring.
Who or what is most important to you?
Who would you advise your supporters to give their second preference to?
I'll leave that up to my supporters. I'm going to give mine to David.