We cannot even define them, let alone name them...

...so how can we make war on those we call terrorists? asks David Whittaker

The rhetoric from Washington about "taking out" terrorism is a predictable response provoked by the anger and grief that followed the horrendous, nihilistic attacks of September 11. Amid such emotion, dispassionate scrutiny of events can be difficult. But someone needs to ask the difficult questions. Perhaps the trickiest one is what we mean by the term "terrorism".

A compound definition runs thus: the premeditated threat or use of violence by sub-national groups or clandestine individuals intended to intimidate and coerce governments, to promote political, religious or ideological outcomes, and to inculcate fear among the public at large. The tendency is for the term to be seen as pejorative.

In studying terrorism, it is helpful to consider the historical, social, economic and ethnic contexts that influence thought, behaviour and action in the areas where it occurs, remembering that only ten countries bear the brunt of three out of four incidents.

The descriptions of such acts and their perpetrators have changed frequently. After 1945, there was the anti-colonial "freedom fighter" in Asia, Africa and the Middle East. Then there were nationalistic separatists in Quebec, Palestine and Spain. State-sponsored terrorism became a rising threat in the 1980s. Social and economic disadvantage have fuelled violent protest in Arab countries, Latin America and Sri Lanka.

We have to consider "terrorism" in terms of its constituent elements - terrorists. They may be heroes and admired trailblazers. Some - in Cuba, Kenya, Cyprus and Israel - have made the transition from hunted insurgent to state president. Today, there are at least 50 or so terrorist groups, ranging from those with a simple structure and platform to groups with a complex network and deep-rooted history.

What is it that leads people to resort to terror? Research shows that social and economic grievances and ethnic and religious discrimination are motivators. These can affect even the highly educated, who may become disaffected - as happened in Germany and Italy in the 1970s. Government reaction to protest that is seen as repressive and unjust can precipitate terrorism, making violence possible and sometimes morally acceptable.

A US Army Terrorism Research Center study lists three principal types of motivation for terrorists - rational, psychological and cultural. Terrorists acting rationally make a cost-benefit analysis that assesses a target's defensive capability against their own capabilities to attack. Outrages in New York, Kenya, Beirut, Oklahoma and Omagh are instances of this. However random an attack, maximum publicity in the media is a calculated benefit. Psychologically, the terrorist is dedicated, intolerant of dissent among collaborators, and resistant to any compromise. Cultural motivation projects message and myth often not readily intelligible to those from other traditions.

Although more than two decades of struggle between violators of the peace in Sri Lanka, Argentina, Peru, Colombia and Northern Ireland may be understood as a popular warlike conflict in the Clausewitzian sense, war, in a generalised sense, does not seem a realistic way of preventing, locating and containing terrorist flashpoints. War is an armed conflict between states. Terrorism is regarded more usefully as a breach of the peace in which non-state entities participate. The breach is localised and specific in intention and may take the form of a protracted series of unpredictable attacks or the odd cataclysmic operation.

Internationally, there has long been concern to fight terrorism as a social malaise. In November 1937, the League of Nations drew up a Convention for the Suppression of International Terrorism. Other international instruments have followed, but the International Law Commission, a United Nations subsidiary, is still wrestling to provide a workable definition of terrorism, with lawyers tending to fall back on ethical considerations - "terrorism" indicating community condemnation of an act - rather than rigorous legal terms.

So we are back where we started, peering out at a multiplicity of hostile intent, threat and action, without an umbrella label and lacking an "open sesame" to reduce the global incidence of terrorism. But the countering methods of shared intelligence, the meticulous police investigations of Interpol, the control of borders and personal travel, the scrutiny of associated money laundering and drug dealing are growing in effectiveness. States have also been seeking to pool warnings about hijacking and threats of nuclear and biological weapons. It is along these lines that we must continue to find a solution to the lawlessness of terrorism, rather than through a blanket declaration of "war".

David Whittaker is a former lecturer in international relations at the University of Teesside and editor of The Terrorism Reader , published by Routledge, price £16.99.