The Prime Minister's decision to convene a judicial inquiry into Bloody Sunday in Londonderry in 1972 has been warmly welcomed in some quarters and challenged in others. I wish to deal with the objections.

"Will it help the peace process or merely open old wounds?" say doubting Ulster Unionists. "Why not hold inquiries into massacres perpetrated by the Provisional IRA?" I even heard someone query the validity of such an inquiry after the passage of 26 years.

Dealing with the last objection first, if our experience of time was linear that query would hold water. But if there's one lesson The Troubles has taught the unhistorical English it is that the Irish do not comprehend time as a straight line. We think they live in the past, but it is the past which lives in them. That reality is common to all.

Historic events like the Battle of Britain and Bloody Sunday do not stand on some unchanging plateau outside time, they move with it. It is our nature, our need, to re-experience events, which is why we have anniversaries; we don't move away from historic events, they follow us.

Are the Dead Sea Scrolls, unearthed in 1947, invalid because the world from which they came has gone? The sinking of the Titanic and the Munich Air Disaster would not continue to arouse intense emotions if the past simply remained in the past, beyond lived experience.

If that was so, justice as a concept would perish; the world would simply resign itself to fatalism. War criminals would not be pursued, the Guildford Four and the Birmingham Six would still be in prison, the late Captain James Thain would still be blamed for Munich.

The Provisional IRA could apologise for its atrocities, as could the Ulster Volunteer Force. However, neither group can be subjected to a judicial inquiry because, unlike the army or the police, its members are not representatives of the law. They can be tried for acts against the law; but they cannot be investigated for breaking what they never pledged themselves to uphold.

The purpose of the Bloody Sunday inquiry is to examine whether members of the First Paratroop Regiment in Londonderry acted unlawfully by shooting civilians indiscriminately, and whether they acted upon military orders.

Why is this important? Firstly, one consequence of Bloody Sunday was an escalation of violence which, in March the following year, led to the first IRA bombing of mainland Britain.

Secondly, Bloody Sunday confirmed all the anti-British propaganda - ignoring the fact that in August 1969 British soldiers were welcomed by Belfast Catholics as a lawful armed defence against the attacks of Loyalists and Protestant B-Specials.

The murder of 15 Catholics in the Loyalist bombing at McGurk's Bar in Belfast the month before Bloody Sunday merely confirmed Nationalist fears. But Bloody Sunday removed all doubt about Britain's role and won international sympathy, support, as well as recruits for the Provos.

I don't know if the inquiry will damage the peace process, nobody does. Peace will only work if the people of North and South want it sufficiently to disown the gunmen. To do this they have to trust the British and Irish Governments.

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