Yet more complexity, this time from Professor Malcolm Shaw, Sir Robert Jennings professor of international law at the University of Leicester:
The question of the legal justification for the use of force against Iraq in March 2003 has been long and ferociously debated. Most international lawyers regard the action as illegal, but not all.
One interesting question is whether the standard required to demonstrate a legal justification for force is that of "a reasonable case" or something higher. The use of force in Kosovo in 1999 demonstrates that while a vast majority of international lawyers regarded this at the time as unlawful (although some have since changed their minds), at no time could it really have been said that any standard higher than a reasonable or credible case was either accepted or posited.
In any event, once the question of legality is dealt with, the next, and perhaps equally critical issue is whether the proposed action is right.
What a predicament: most international lawyers, but not all; the use of force in Kosovo also problematic from a legal point of view; and the question of legality non-identical with the question of what is right. It's enough to give your average Guardian-reader a headache.