How to judge soldiers whose cause is unjust

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?”[1] 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.”[2] 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.”.