There is a funny passage in a Michael Dorris novel when a Catholic priest comes to a reservation to evangelise a tribe of North American Indians. He asks an Indian how to say Hello in their language and is given the phrase. Every time he uses it the Indians burst out laughing because what he is actually saying is, "I smell like dogshit."

James Bowyer Bell has devoted his entire adult life to the study of conflict, specifically those organisations engaged in guerrilla warfare out of genuine grievance, but also including those he describes as Euroterrorists - Germany's disbanded Red Army Faction and Italy's Brigate Rosse. There is no doubt that over a long period of time he got close to many insurgents and veterans, Ireland and the IRA in particular being his specialist subject. Indeed, what journalist or student of politics or history did not reach for Bowyer Bell's The Secret Army or Tim Pat Coogan's The IRA in the early 1970s in order to understand the background to, and re-emergence of, physical-force republicanism?

Yet now, with this book, Bowyer Bell's swansong on the subject, I wonder exactly who on the reservation he was talking to for all those years. It is not that the mind of the rebel he depicts is completely unfamiliar, but his resort to metaphysics and his use of transcendent language, in the style of those spiritual first-aid books that proliferate in the USA, are completely incongruous with the subject.

Membership of "the underground", he asserts, is based on "faith" in "the absolute truth"; and, above ground, there is the ecosystem, "the community of the faithful", which he compares to "a galaxy, a great whirling light source that pulses with energy". Unfortunately, his sustained metaphors, rather than illuminating, tend toward unintelligibility: "Within the galaxy the major factor is the movement that gives shape and purpose through the organisations of the faith."

While there are many valid comparisons to be made between the various guerrilla groups around the world, he tries too hard to write a unified theory of insurgency ("All are different and yet all are the same"; "the faithful act everywhere alike"). To do so he has to engage in a little bit of physical force himself, a bit of Procrustean sawing and stretching. Apart from the fact that, just like governments, they use violence for political ends, I would draw a major distinction between the psyche and zeal of the Hizbullah suicide bomber and that of an IRA volunteer operating in a completely different political and cultural context and whose political options are greater.

Having said that, there is a lot of provocative reading in this book, about the nature of organisation, control, targeting, communication, counter-insurgency, which will probably appeal more to the specialist than the lay person. Bowyer Bell opposes the orthodox view of the "terrorist stereotype" and argues that they have to be understood on their terms, their determination to seek justice, though some movements with unfathomable demands are beyond co-option or compromise. Reassuringly for governments, he says that "Most revolts, including classical armed struggles, fail; some are co-opted, a few triumph, and others simply persist".

The most traumatic time for any revolutionary organisation, he says, is the ceasefire, the truce, which brings it to breaking point over the articles of faith. In El Salvador the FMLN abandoned certain aspirations and assumptions in order to share some power. "The negotiated accommodation was made practical because the dream had shifted over time."

In the North the armed struggle was fairly unique in that it didn't fall into any classical category. The liberated territory was - and is - in the minds of a section of the nationalist people. The landscape of the struggle was a West European consumer society, with sectarian divisions, with vestiges of social democracy, tied through the union to the historic enemy.

The one constant in a rebel career, says Bowyer Bell, is the prospect of a broken heart: obsolescence in defeat, or obsolescence in victory when the underground surfaces to claim not the dream, but to serve a conventional purpose. I think not. The rebel is of the people. And people, their lives and their livelihoods, are ultimately the things that really matter.

Danny Morrison is a writer and the former national director of publicity for Sinn Fein