Leading article: Sharon, of all people, has given us a reason to believe

It almost does not matter what Mr Sharon's motives are in pressing ahead with the disengagement. Certainly, he is under pressure from Israeli hawks, led by the former prime minister Binyamin Netanyahu, to use it to consolidate Israel's grip on the West Bank - apart from the few small settlements there also scheduled for disengagement. And, certainly, Mr Sharon's contribution to the peace process has in the past been mostly destructive. But it may be that only a hawk could have begun the dismantling of these settlements. And the fact remains that this is a hugely important step in the right direction that at least makes possible a return to the road map towards a lasting peace based on the two-state solution.

Two cautions. One is that we should not go along with the game of setting up Mahmoud Abbas, the elected Palestinian leader, for failure. It is sometimes implied that if Mr Abbas could make a success of the mini-statelet of the Gaza Strip, then the Palestinians might earn the right to administer some of the larger West Bank. Given the weakness of Mr Abbas's grip on the apparatus of the Palestinian Authority, this is likely to be used as a means of obstructing a lasting Israeli-Palestinian deal. It is significant, though, that suicide bombings in Israel have reduced sharply. Yet, as has been the case since at least 1967, the most important force for progress towards such a deal remains sustained American pressure on the state of Israel.

The other caution is that we should not set too much store by the hope that whatever progress is possible will diminish the threat of jihadist terrorism. For Osama bin Laden, the presence of US troops in Saudi Arabia was always more important than a liturgy of grievance that always recited Palestine. Tragically, the invasion of Iraq has provided an easy alternative source of resentment on which jihadist terrorism can feed. But any advance in the Israeli-Palestinian peace process ought to help to persuade moderate Muslim opinion of the falsity of Bin Laden's claim that a Zionist crusader coalition is waging war on Islam. And it could kick a crutch away from the self-pitying propaganda that sustains undemocratic Arab regimes across the Middle East.

That is, to be sure, to allow optimism to run ahead of the bitter lessons of experience - including recent experience of George Bush's reluctance to apply meaningful pressure on the Israeli government. But it is as well to be aware of what is at stake. The Gaza pull-out at least makes an optimistic future possible. Without it, there would be no hope. For once, therefore, let us praise Mr Sharon and wish him well.