But the question is, what can we negotiate? As you're aware, in any negotiation there are two or more parties, all of whom may have different and competing objectives. A negotiation involves those parties coming to an acceptable compromise while having the authority to reach that position.
Using Northern Ireland as an example:
1) The IRA had a not unreasonable final objective, which was a united Ireland. They weren't going to achieve that in the short term but it wasn't totally unattainable in the long term. Their fall-back positin was at least to be able to take come part in government and have equal civil rights.
2) Both sides had a well-organised hierarchy with people who could set terms and agree outcomes.
3) They had the political machinery to take part in the subsequent power-sharing arrangements.
4) We were able to negotiate an outcome that didn't meet the republicans' full demands and certainly sank to high heaven as far as the Loyalist community were concerned but was deemed by both parties to have moved far enough towards, or not too far from, what they wanted to achieve.
5) There were those on both sides who didn't accept the outcome and were marginalised but the central powers of each movement had enough authority to be able to enforce the outcome and make it work, as well as isolating the extremists.
There's undoubtedly still a lot of sectarian feeling though, which might take generations to subside, if it ever indeed does. You could apply the same set of parameters to most of the negotiations that have taken place over the years between governments and liberation movements.
But applying those five conditions to ISIS dosen't give the same answers:
1) Their stated objective is a caliphate over countries which don't want that.
2) They appear to be a loose grouping, without a central leader, and where there are "affiliates" that are part of the network in name only. You could come to an agrement in Iraq or Syria but not in Yemen or Somalia. This is mirrored in the set-up of Islam generally, where there is no single authority and control is often down at individual mosque level.
3) It will be all or nothing for ISIS, who are religious extremists and who reject the concept of politics or democracy as 'unislamic'.
4) What could we offer them and they offer us? At best, it would be "If you stay where you are and don't bother us, then we'll leave you alone".
5) Any group that didn't accept a negotiated would carry on fighting, probably even more violently than before.
Of course, you're right to say we should rule nothing out, however improbable, but this isn't a Conan Doyle short story. A few on here have said that, as a relatively young religion, Islam is going through its own Dark or Medieval age and it will take an equivalent Renaissance to change hearts and minds.
This isn't a Conan-Doyle story? No shit, Sherlock! (sorry, PB, couldn't resist that one :) )
You raise without doubt some very difficult long term questions. I do not disagree for one minute that the conditions in which a negotiated settlement could be achieved do not currently exist, and do not look like they will exist for a very long time. I, unlike others who have contributed to this discussion, do not pretend to have a crystal ball in which I can see the future. However I do remain persuaded that since military means alone will not provide the answer either way, eventually there will have to be some form of consensual resolution, because the alternative is in effect a perpetual state of war. How long that process takes is a very moot point: the Irish process took decades, and the Palestinian issue is still not resolved and shows no signs of a resolution any time soon.
To answer your points as best I can however:
1. It seems to me that the objective of the caliphate is closer to replicating the Irish experience than any of the other points raised. In Ireland, both dogs lay claim to the same bone. They couldn't both have it, it was 'either/or'. It seems to me that exactly the same is true of the caliphate. Yet in Ireland eventually a settlement was achieved.
The suggestion, by the way (not one of yours) that the IRA cannot provide a true comparable because they did not have suicide bombers seems to me one of the more facile points that has been made in this thread, and that's saying something. Apart from anything else, the impact of the suicide bomber is that in addition to the other deaths he causes he is willing to give his own life in order to achieve maximum impact for the Cause. So what did Bobby Sands and the others do? Their paradise might have been the vision of a united Ireland and the immortality of hero status and knowing songs would be sung about them within the Catholic/ republican community, but the dream and the way of achieving it is essentially the same.
2. It would not be the first time in history that there has been negotiation between one side with a centralised command structure and another side that has no organised leadership or structure. Negotiations between Claudius and the native British population provides one early example, consisting as it did at the time of various warring tribes. King Alfred negotiated on behalf of Wessex with various clans of marauding Danes. The British negotiated with the native Americans in settling the thirteen colonies.
It seems to me two things might happen. The first is that whilst there may not be as you say a hierarchy, there is undoubtedly something in the nature of a communications network between the various factions of the radical Islamist movement. They talk to each other. In those circumstances, in theory at least, the possibility that particular individuals could be delegated to negotiate on behalf of the entire movement, or at least a substantial majority of it, is a real one. The second possibility is that, as with Claudius, separate truces are negotiated with separate areas. So perhaps the peace in Syria is not the peace in Yemen, and so on. I do not for one minute underestimate the difficulty in such an undertaking, but I cannot accept that as being an insuperable obstacle.
3. The point that IS/AQ are engaged in an 'all or nothing' strategy, and that they entirely reject the values that the west holds as universal truths and inalienable rights seems to me to be another way of putting the first point namely that, as in Northern Ireland, the ultimate objectives of each side are mutually exclusive. To repeat the dogs with a bone analogy, if two dogs are fighting over one bone, there isn't much to negotiate about. Either one gets it or the other does. So the prospects of a negotiated compromise appear slim.
However that was just as true in Ireland, and the failure of talks in the early/mid 1970s seems to me to underline that point rather than undermine it. So again it seems to me that ultimately a negotiated solution, in the very long term, is the most likely outcome: granted, we have years of struggle ahead of us before we get to the point where the other side is even thinking about negotiations.
4. It might be enough to say 'you leave us alone and we will leave you alone'. It might be that a land-rich Islamic country might be willing to give up a certain amount of its territory in order to allow a caliphate to be established on a permanent and recognised basis. It might be that a number of Islamic countries make a smaller amount of territory available in which autonomous sub-caliphates can be established. It does not seem to me that it is beyond the wit of mankind to devise a solution that in time is acceptable to both sides. Nobody is ever happy after a compromise, but that is not to say that compromise is by definition wrong.
That said, there is undoubtedly a hard core school of thought within radical Islam that suggests that nothing short of the destruction of western society and the imposition of global sharia law is acceptable. Plainly there can be no peace, let alone negotiation, with such a mindset, and one of the preconditions for negotiations would have to be that there is enough of a groundswell for talks aimed at achieving a lasting peace to be meaningful. That will not happen any time soon, I grant you, but it is a big step to go from there, as many in this thread have done, to saying it will never happen at all.
5. It is true that whenever you impose a solution that 90% can live with, the other 10% is often inclined to go its own way. We have seen that too in Northern Ireland, with the 'real' IRA. This is probably a restatement of point 4 - that some will never accept a peace on any terms. Maybe not, but that doesn't mean that a peace with those who will isn't worth having, as in Ireland. Perhaps the ongoing existence of a certain amount of residual resistance is a price worth paying for a wider peace.
I have referenced Ireland a lot because to me it seems that there is a lot we can learn from that situation, if we understand how the lessons are properly to be applied. However it is not the only historical parallel: the Palestine/Israeli debate has been done to death in a million other threads, but for the purposes of this thread it is enough to note that the dispute rumbles on. Maybe as in Ireland, that dispute, and maybe like the war on terror, will take a good 70 or 80 years to resolve.
