Forty years ago today - October 30, 1972 - the British Government, led by the Conservative prime minister Edward Heath, published The Future of Northern Ireland: a paper for discussion.
It was the first substantive policy initiative following the prorogation of the Northern Ireland parliament eight months earlier and, among other ideas, it set out 'some unalterable facts about the situation and some vital conditions which must be met'.
Three of those 'vital conditions' have remained in every other policy initiative since then: proportional representation for local elections, power-sharing arrangements to ensure that the nationalist minority would be represented at executive/cabinet level and an Irish dimension, which would allow both the British and Irish governments to jointly underwrite any new agreement. Coming so soon after Stormont had been stripped of power and then mothballed, and against the background of what is now regarded as the bloodiest year of the Troubles, the discussion paper came as a huge shock to unionists.
Indeed, a matter of weeks before the Government's paper, the local parties had been invited to present proposals of their own at a conference in Darlington.
The UUP had made provision for Opposition structures and for some committees to be chaired by either Alliance, or the SDLP, but it wasn't power-sharing as we understand it now.
Also, it didn't favour proportional representation, although it was agreeable to - given the right circumstances - 'an Irish intergovernmental council ... to discuss matters of mutual interest, particularly in the economic and social fields'.
The DUP, meanwhile, 'adopted the general attitude that, since the restoration of the NI parliament ... is extremely unlikely ... NI should be fully integrated with the rest of the United Kingdom'.
The SDLP had no interest whatsoever in an internal settlement. Their proposals, Towards A New Ireland, included: a declaration by Britain that it would facilitate Irish unity, a new treaty between Britain and the Republic accepting 'joint interim responsibility for the administration of NI' and the setting up of a national senate to 'plan the integration of the whole island'.
Looking at those proposals now and remembering Seamus Mallon's comments, 25 years later, that the Belfast Agreement was "Sunningdale for slow learners", it's difficult not to conclude that it's the SDLP which has, in fact, drifted furthest from its original position.
On March 8, 1973, a border poll, albeit boycotted by nationalists and republicans, indicated very substantial support for Northern Ireland 'remaining part of the United Kingdom' and, a few weeks later, the Government presented to parliament a set of constitutional proposals, including provision for a Northern Ireland assembly (elected by proportional representation), a power-sharing executive committee and, following the elections, a conference involving representatives from the assembly and from the British and Irish governments.
While it is true that there were setbacks here for the UUP, they were nothing on the scale of the setbacks for the SDLP.
Instead of the British indicating that they would facilitate unity and work with Dublin to achieve it, the proposals made it clear that Northern Ireland would remain part of the UK 'for so long as that is the wish of a majority of its people'. That constitutional guarantee became the fourth 'vital condition' of any new agreement.
The consequence of this setback for the SDLP was that they chose to play hardball on a council of Ireland structure being built into the Sunningdale Agreement at the end of 1973.
They needed something to show their supporters (and it needs to be remembered that the SDLP was much 'greener' then than it became), as well as a trophy to 'encourage' armed republicanism that dialogue and democracy worked.
But the knock-on effect of insisting on the council of Ireland was to destabilise Brian Faulkner's leadership of the UUP and force the bulk of his party into a pact with the DUP, Vanguard and elements of the UDA - leading to the Ulster Workers' Council strike, which brought down the new assembly in May 1974.
It was, actually, a massive tactical error by the SDLP, which also totally underestimated what it had taken for Faulkner to persuade his party to back power-sharing in the autumn of 1973.
For the next couple of decades, the parties and governments danced around each other: all pushing key elements of their own agenda, yet all aware that power-sharing, an Irish dimension, proportional representation and the 'constitutional guarantee' were the essential ingredients of any agreement - irrespective of how they were actually mixed.
The final element, though, was the concession from unionists that Sinn Fein should have a full role to play if the IRA renounced violence and accepted democratic practice alone.
And that's where we are today, exactly 40 years on.
Or maybe not. I'm not convinced that we have genuine power-sharing yet, let alone any sense that unionists and nationalists are working together in common cause.
They are where they are today because there was nowhere else for them to go - and it has taken them four decades to reach that conclusion.
The next stage - for a post-conflict generation, perhaps - is to lift politics here from the rut of veto and stalemate and focus, instead, on a new era and new opportunities.