WHEN political judgment is cast there is always the problem of the silent testimony of those who cannot be heard because they have died, either because of bloody events or the passage of time.

But there is a kind of double silence in the case of those of whom we can never know whether they might have died had the circumstances transpired differently.

It is the difference between the known unknowns and the unknown unknowns. What would those who would have died had the Troubles in Northern Ireland continued be contributing to the current debate around the On The Runs scheme? A debate which would not exist because the slaughter in the Six Counties might be continuing unabated? Good luck getting your brain around those alternative histories.

Many historical judgments on Tony Blair's time in office tend to the harsh, whlch may explain the closing of ranks which has seen the Chilcott inquiry into the origins of the Iraq invasion gather dust in spite of being heavily redacted. With Islamic State rampant and a fascistic variant of Islamism seeing slaughter on the streets of Paris, the war on Saddam Hussein is being judged ever more harshly except, perhaps, oddly, in the new upper echelons of Scottish Labour.

But Prime Minister Blair's legacy from the Good Friday Agreement is more robust, commanding far wider support, in England where there is in the main disinterest in the issue, and in the Province where there is tangible relief that the slaughter has abated.

Achieving that took courage and pragmatism. In the GFA the issue of prisoner release was dealt with but only in subsequent negotiations did Sinn Fein raise the question of the status of Republicans who were at large but wanted to know their legal status - the On The Runs. An unofficial deal was done to allow this, a deal which came out when the 2014 trial into the 1982 Hyde Park bomb trial collapsed.

Mr Blair has as so often got much wrong. He was arrogant in saying his "busy schedule" would prevent him submitting himself to Westminster's Northern Ireland Affairs Committee until virtually coerced into appearing by the Speaker, to whom credit is due.

He admitted that the On The Runs scheme was a flawed, ad hoc system of gray areas, "not an amnesty" but "not a secret" - both arguably untrue. But he is the ultimate political pragmatist, possessed of huge self-belief and certainty that ends justified means.

There was a telling flash-point when Mr Blair turned in exasperation on North Antrim MP Ian Paisley, son of a man who had made a journey, and said: "You sit in the decision-making chair for a minute." He told North Down MP Lady Sylvia Hermon: "If we'd simply said we're not going to deal with this issue at all, I personally believe it would have had a very serious impact on the process."

On Iraq the process and outcome were demonstrably wrong. In Northern Ireland the former is open to question but the latter is not.