Could you bring yourself to shake the hand of a terrorist who you knew had killed people? It's one of the most basic human gestures of all, but one that is loaded with symbolism, says Jonathan Powell.
I was Tony Blair's chief of staff and in 1997 I accompanied him to the first meeting of a British prime minister with the Republican leadership since 1922.
It took place in a small windowless room in Castle Buildings in Stormont. I did not feel well disposed to the IRA. They had ambushed my father near Lough Neagh in Northern Ireland during World War II and shot him through the ear. My brother, who had worked for Margaret Thatcher, had been on their death list for eight years.
I couldn't bring myself to shake hands with Gerry Adams and Martin McGuinness when we met. I regretted it later. It seemed childish. Tony Blair shook them by the hand to show them the same respect as he would any other human being, as he said after the meeting. He paid a price when he was mobbed afterwards by Democratic Unionist Party (DUP) supporters throwing rubber gloves at him.
Peter Sheridan from Londonderry, the top ranking Roman Catholic officer in the RUC, survived assassination attempts at the hands of the IRA and had to move houses three times in his native Derry. Martin McGuinness had been a commander of the IRA in Derry and yet Mr Sheridan shook Mr McGuinness's hand after they met in Downing Street for the first time in 2006, the first formal meeting between the police and the Republican leadership ever.
It can be hard for democratic politicians to reach out to those they consider terrorists. David Trimble led his Ulster Unionists into talks with Sinn Fein. He would not speak to them directly but would only engage with them through the chairman of the talks, George Mitchell. Mr Adams could not resist trying to start a conversation with him, even pursuing him into the gents. All such persistence did was irritate the Unionists.
Even when negotiators feel, as former UN special representative James Lemoyne told me, "like punching [the terrorists] on the jaw or carting them off to jail," engaging them as human beings can pay dividends. Negotiators locked into talks with terrorist leaders have cooked for them, got drunk with them, played with their children and listened to their problems.
But not every negotiator agrees that good personal chemistry between the participants is important in making talks work. Yair Hirschfeld led the Israeli team at the Oslo talks which brought Israel and the Palestinians closer to peace than any negotiation before or since.
"There's a lot of nonsense talked about this," he says. "You don't need to be friendly to make a deal."
And the mobile phone? It has changed all our lives, but the ease and availability of the ubiquitous mobile has made it a vital tool in reaching out to terrorist groups and exchanging information.
After all, with a cheap disposable mobile you can speak from anywhere in the world, without anyone identifying where you are. The person you are speaking to could be deep in the jungle, holed up in the centre of a mega city - or even sitting in the cafe next to you.
When British official Alastair Crooke came to negotiate with Hamas during the second intifada, he sent his driver to sit up on a hill above Bethlehem, watch the outbreaks of fighting and relay the locations to him so he could move around the back alleys of the city in an attempt to stop the two sides fighting.
In Northern Ireland, loyalist and republican leaders would speak to each other on mobile phones to marshal their supporters and avoid conflict during street demonstrations.
Many negotiations with rebel groups have been facilitated by mobiles, sometimes with swapped SIM cards.
When Michael Vatikiotis, the Asia director of the Centre for Humanitarian Dialogue, was brought in to negotiate with the Red Shirts in Bangkok, he discovered that though the rebels hadn't spoken face to face with the government, they were being phoned by government ministers on their mobiles and conducting ad hoc negotiations on the move.
He had to persuade the Red Shirts to put their demands down in writing, rather than relying on unstructured negotiations with the authorities.
But is it right to engage such groups in talks at all? It is entirely natural that those who have lost loved ones in atrocities carried out by them, or been maimed themselves, should think talking to them is simply wrong.
But it remains a fact that over the years the British government fought with The Stern Gang, Archbishop Makarios and Jomo Kenyata, labelling them terrorists, but then negotiated with them as statesmen. It did the same with the IRA.
It is all too likely this historical pattern will be repeated yet again, even if at the moment it seems unthinkable that we would ever speak to Hamas, the Taliban or al-Qaeda. But one day we may find ourselves sitting down and negotiating in the same room as them.
So could you shake hands with Mullah Omar or even Osama Bin Laden?