At home in Derry John Hume broods on what motivates the unionist No campaigners. Is it a case of fighting the Scottish Premier Division for ever and ever, with the same team taking the honours again and again? No room for Celtic in their philosophy, he feels.
"What is their alternative to the agreement? Are they looking for victory, and do they think that victory is a solution?" he asks. "I have thought long and hard to try to find the logic of the No campaign. And given that they have refused to produce an alternative, it would appear to me that they are looking for a Rangers versus Celtic match, with a victory for Rangers."
Thirty years in politics and Mr Hume is in sight of an agreement of which he is the chief architect. This is a time of opportunity and anxiety. But what happens next is really out of his hands. Most nationalists favour the Belfast Agreement. Unionists though - who can read how the majority in that tradition will vote? Over the next 24 hours undecided unionists must battle with their thoughts and their consciences.
Unionism should grasp the current opportunity with hope and affirmation, he argues. "One of the tragedies of the unionist people is that in the past their leaders tended to look inward. They never built a relationship with the rest of the world. They should be building a relationship with that world, including their nearest neighbour."
Unionists should also realise that if the agreement is destroyed, then the initiative will be back with the British and Irish governments. "The British and Irish governments would take the decisions about the future of Northern Ireland, and we would have no say whatsoever. So what is wrong in unionists building a relationship with the South without losing their identity?"
Hope and anxiety are the emotions written across Mr Hume's countenance. It's been like that for a few years now, going back to Hume-Adams in 1993. He needs a long political break, but that can't happen until at least after the referendum and the assembly election. This is the great moment in recent Irish history. Over 30 years of community work, civil rights activism and SDLP politics have been leading inexorably to this critical juncture. He is a difficult politician to interview. He is an intelligent and rounded man; in the right mood he can be witty and interesting. He taught history and French, travelling in France in his formative years. He was a leading light in the credit union movement. In his book Personal Views, published three years ago, he quoted appositely from Joyce, Yeats, Swift and his great influence, Martin Luther King. He can sing a song; he played cricket as a youngster.
But there's no point in widening the conversation to music, or literature or drama, or sport. He'll just adopt an air of distraction and bring the conversation back to politics now. His passionate concentration is total.
At least Mr Hume realises that he's obsessive. In the months leading up to the talks agreement, journalists would badger him for comments. "What's the point? I'll just give you my usual single transferable speech," he'd joke, citing the jibe unionists have used against him. Reporters would nonetheless need their sound bite, and dutifully Mr Hume would launch into "an agreement that hurts no one", "an agreed Ireland", "spill our sweat not our blood", and so on.
But while the language has become hackneyed, he still maintains that the thesis that it supports is the only basis for a realisable agreement - an agreement that accommodates two traditions. He says that for all the condemnation heaped on the agreement, its opponents have posited no alternative, apart from Rangers versus Celtic in perpetuity.
"The basic message is that the people of the North and South realise that they will be casting the most important vote of their lives on Friday. It will be a historic vote. They will be voting not just for themselves but for their children, and grandchildren. Their votes will be laying the foundations for future generations. They will be laying the foundations for lasting peace and stability."
Mr Hume says he can understand concerns about prisoners and decommissioning. But what surely is of greater concern is that this agreement can bring an end to violence - that it can prevent more people joining the IRA, the UVF and the UDA.
"Young people were sucked into violence by the handed-down philosophies of both traditions. On the republican side you had the Padraig Pearse syndrome, or the dying-for-Ireland syndrome, where it was patriotic to die or fight for your country. On the loyalist side it was patriotic to defend Ulster. That was all witnessed on the streets in the Bloody Sundays, the La Mons, and the Enniskillens of this world."
Mr Hume says unionists should acknowledge how far nationalists had come in 30 years. They had compromised and taken risks. Now was the time for unionists to take a chance on the agreement, to test it. "Every nationalist party including Sinn Fein accepts that a solution must be by agreement and consent. Could I gently and proudly remind people that when the SDLP was founded in 1969-1970 consent was written into our constitution?" If this works, Mr Hume's single-track personality should change, as will his language and conversation. There will be things to talk about other than Northern Ireland politics. He will be able to stand back from his obsession, and maybe even enjoy life. For the coming period though, the focus can only be on one subject.