For all the millions of words written and spoken on the Northern Ireland problem, the gulf in comprehension between unionists and nationalists remains dauntingly large. This came home to me in a political debate organised last week as part of the West Belfast festival.

The pro-union members on the panel were generally listened to with politeness, but with little evidence of any understanding which could begin to bridge the gap. My fellow panellist Ruth Dudley Edwards found the audience "as brainwashed as North Koreans".

Similar, if less extreme, thoughts came to mind on reading Dr Garret FitzGerald's article on decommissioning (The Irish Times August 7th). As one of the most intelligent and moderate of nationalists, I had hoped for an in-depth analysis. What we got instead was the tendency to go easy on Sinn Fein/IRA, while reserving most criticism and suspicion for unionists.

Dr FitzGerald says he failed to anticipate that decommissioning would become a sticking point. His interpretation of the Belfast Agreement is that it contains a provision postponing decommissioning until after the formation of the executive.

David Trimble is described as failing to sell the agreement enthusiastically to his supporters, and impaling himself on the hook of decommissioning, implicitly leading to the current impasse.

As someone who spent much time negotiating the Belfast Agreement and then continually selling it to unionists, I can say that I know of no such above provision. There was no mention in Dr FitzGerald's article of a key sentence in the agreement, that "all participants reaffirm their commitment to the total disarmament of all paramilitary organisations". Nor any mention of the aspect of "absolute commitment to exclusively democratic and peaceful means . . . and opposition to any use or threat of force by others . . ".

There was also no expectation by Dr FitzGerald that, 15 months on, Sinn Fein should be held to account about how it means to honour that "commitment". Nor was there any understanding that with commitments not honoured after so many months, unionists would naturally lose faith in the intentions of Sinn Fein and come to fear that the republican game plan is now to set up an unstable "mafia" state.

At the same time, there is no mention anywhere in his article of continuing IRA violence, including last week's murder of 22-year-old Charles Bennett in west Belfast, in clear defiance of the undertaking in the agreement to "exclusively peaceful means". Violence - loyalist or republican - is to be condemned.

IRA members are referred to as Mr Adams's "colleagues", as if we were dealing with some legitimate business organisation.

Instead of facing up to the severe difficulties facing those unionists who entered into the agreement enthusiastically and wholeheartedly, Dr FitzGerald lamely appeared to endorse the republican fiction that Sinn Fein and the IRA are two separate organisations. Sinn Fein signed the agreement, but the IRA "with their different decision-making composition" cannot realistically be expected to keep it.

Few things can be more calculated to undermine unionist confidence in republican intentions than this attempt to pretend that Sinn Fein has no clear linkage with the IRA.

When we assented to an agreement which was vague in terms of the timing and steps required for decommissioning, it was to allow republicans space and time to work out how they were to honour the clear commitments made in the agreement. We listened to those who exhorted us to take political risks, and put on the back burner our natural inclination to want a clear contract.

The size of the risks can hardly be doubted. Unionist support in the referendum was little over 50 per cent, in marked contrast to the near unanimity on the nationalist side. Those who argued for such risk-taking cannot now return and say that we should have pinned down every last detail on decommissioning.

Dr FitzGerald also plays down the importance of Mr Blair's side-letter. In this letter, Mr Blair said he interpreted the agreement as meaning that decommissioning should begin straight away.

I remember no howls of indignation from Dr FitzGerald, or indeed from any other nationalist, complaining then about the supposed inaccuracy of the letter. Dr FitzGerald's view is that the letter was necessary to sway unionist voters on the day but subsequently proved to be counterproductive. He says nothing about the need for a prime minister to keep his word in such delicate circumstances.

Most notably, Dr FitzGerald takes at face value the view that a "seismic shift`' in republican intentions took place last June. After a series of face-to-face meetings with Sinn Fein in Castle Buildings, David Trimble could find no evidence for any such change. Gerry Adams confirmed this in his Guardian article of July 13th, in which he said the IRA had stated no intention to decommission and he did not know why Mr Blair expected decommissioning to begin shortly after the executive was formed.

Unionists will have grave difficulty in understanding why someone of Dr FitzGerald's standing should write in these terms and in particular why he should take British government and Fianna Fail "spin" at face value.

It is not as if this was the first time the two governments had got it wrong. Much the same happened at Hillsborough at Easter when we were assured that Mr Adams had agreed to begin decommissioning. At Easter, just as in July, Mr Adams subsequently denied that he had said any such thing.

It is not surprising that with this view of the situation, Dr FitzGerald should recommend that an executive be formed based on a revived IRA commitment. I am one of those who fervently hopes that an inclusive executive - unionist, nationalist and republican - can be set up, but I have to say that unless nationalists such as Dr FitzGerald face up more honestly to the real difficulties, progress will remain difficult.

Unionists will be offended at some of the tone in Dr FitzGerald's article. Unionist political leaders are described as being distracted by an emotional fear of absorption into an alien Irish state. This of David Trimble who has repeatedly praised Irish economic success and called for greater trade and co-operation. Sinn Fein's untrue accusation that unionists refuse to share power with nationalists is quoted by Dr FitzGerald without criticism. Clearly we all have a long way to go to begin to comprehend one another.

Dermot Nesbitt is a senior negotiator and UUP Assembly member for South Down