Without doubt, terrorism is one of the most vehemently debated subjects in current political affairs as well as in academic discourse. Yet, although it constitutes an issue of general socio-political interest, neither in everyday language nor in professional (political, legal, or academic) contexts does there exist a generally accepted definition of terrorism. The question of how it should be defined has been answered countless times, with as much variety as quantity in the answers. In academic discourse, it is difficult to find two scholars who use the term ‘terrorism’ in the same way.
While it is impossible to formulate a definition which satisfies everyone, discussing the definition question is indispensable. The necessity to review existing definitions with a view to improving them is especially obvious in legal and political contexts. How terrorism is defined in these contexts has serious consequences, and if we lack clear definitions we run into problems. How can we have laws or take political measures against something we have not clearly defined? Without doubt, there exists a practical necessity for a definition in these fields. It is important to have clear standards for defining terrorism.
In my view, the definition should meet three basic criteria: first, it should cover those cases that we concurrently consider to be instances of terrorism (such as the attacks on the World Trade Center in New York and the Pentagon in September 2001 or those on commuting trains in Madrid Atocha in March 2004). That is, ideally, our definition of terrorism remains close to uncontroversial usages of the term. Second, the definition should abstain from morally judging the act in question. Later I will say more about so called “moral” definitions of terrorism. For now, it suffices to say that defining an action and evaluating it are distinct tasks and should remain so. Third, the definition must identify characteristics that are specific to terrorism alone, characteristics which clearly distinguish it from other phenomena.