Terrorism has been described as 'any method of war which consists of intentionally attacking those who ought not to be attacked'.
Such a definition implies that terrorism is a means of warfare and as such can be adjudged in accordance with the rules of war. Under the rules of war, a principal distinction is drawn between combatants and non-combatants. As in the case of guerrilla warfare, attacks upon the armed forces of the state, state installations et al can be seen as legitimate. Also tactics such as the assassination of political figures, which are essentially terroristic in nature, can be seen as attacks upon the organisers and planners of an occupation or oppression.
However, terrorism goes beyond this through its apparently inherent use of attacks upon non-combatants. Under the principles of 'just war' theory, an attack upon the innocent is unacceptable in any war or armed conflict.
This idea of the unacceptability of attacks upon the innocent (or non-combatants) is underlined by A P Schmid in Western Responses To Terrorism. Schmid claims that 'terrorists have elevated practices which are excesses of war to the level of routine tactics'.
As such he states that terrorist tactics can be classified as the peacetime equivalent of war crimes. By claiming to be fighting a war but not adhering to its rules, it can be argued that terrorists make themselves into war criminals. In other words 'terrorism distinguishes itself from conventional and to some extent also from guerrilla warfare through the disregard for principles of chivalry and humanity contained in the Hague Regulations and Geneva Conventions'.