Having learned my just war theory at Michael Walzer’s figurative knee, for many years I accepted the independence of jus in bello from jus ad bellum unthinkingly. Just war theory consists of two separate parts, one concerning the legitimate grounds for going to war and the other the rules of engagement once war had begun. This two-part view, the “independence thesis,” went hand in hand with the “symmetry thesis,” or “the moral equality of soldiers”: soldiers whose cause is unjust have the same rights to fight and to kill as those whose cause is just. But troubling questions sometimes crowded in. Doesn’t the justice of a country’s cause affect what actions it can legitimately take? Can’t victims of aggression legitimately do things aggressors cannot? Most fundamentally, “how can there be permissibly violent means of pursuing impermissible ends?” Walzer casts glances at these problems when he proposes the idea of a “sliding scale,” in which the rules of war yield “slowly to the moral urgency of the cause: the rights of the righteous are enhanced, and those of their enemies devalued.” He rejects the sliding scale in favor of the weaker qualification, “supreme emergency,” in which the rules of war are overridden “only in the face of an imminent catastrophe.”
Yet Walzer does not discuss the threat the ideas of the sliding scale and even supreme emergency pose for the foundational distinction between jus ad bellum and jus in bello. It’s not hard to see why. To have probed further would have transformed Walzer’s book from a thought-provoking yet highly accessible introduction to the main moral problems of war, as seen through the lens of traditional just war theory and international law, into a dense and difficult philosophical tract. For it’s clear that once we challenge the distinction we find ourselves in murky waters from which there’s no easy escape. The wonder is only that most of those in the just war tradition have for so long taken the independence of jus in bello from jus ad bellum and the symmetry thesis for granted.
These views have now been challenged by Jeff McMahan and David Rodin, and their compelling arguments force us to take the plunge. Rodin poses the problem succinctly:
If an aggressive war is fought within the bounds of jus in bello, then the Just War Theory is committed to the seemingly paradoxical position that the war taken as a whole is a crime, yet that each of the individual acts which together constitute the aggressive war are entirely lawful. Such a war, the Just War Theory seems to be saying, is both just and unjust at the same time.
McMahan offers a detailed argument to show that “unjust combatants”—those who fight for an unjust cause—will inevitably violate one of the fundamental rules of jus in bello, the requirement of proportionality.
At the outset I would like to thank the Professor Judith Lichtenberg for sharing this article. Please accept heartfelt thanks for that.