The two previous chapters described an increased subjection of US air warfare to IL and a rise in the relative importance of the logic of efficiency in target selection over the same time. Do these parallel developments suggest that IHL indeed makes a difference for behaviour in war? Based on the findings so far, can I claim that recourse to law has caused the observed change in what the US military considers a legitimate target and chooses to attack from the air? One could interpret such a claim to imply the assertion of a law-like relationship between IL and the logic that combat operations follow: if belligerents comply with IL, warfare accords with the logic of efficiency. Yet the study of only US air warfare is clearly too limited in scope to warrant such a sweeping conclusion. In addition, the finding of section 6.2 is not that warfare follows one logic at first, but abruptly switches to the other the moment IHL is allowed input into decision-making. The change in logics is gradual and in relative importance.

Of course, we can alternatively conceive of causality in probabilistic terms. But the previous chapters alone would not warrant the corresponding conclusion either – that recourse to law in warfare increases the likelihood that the definition of a legitimate target of attack by decision-makers accords with the logic of efficiency, whether that likelihood is small or large in absolute terms. All that the study of US air warfare has so far shown is that a change in the role of law in war, on the one hand, and a shift in the logic that combat operations follow, on the other hand, correlate in time. In order to move beyond a mere observation of parallel developments, I need to demonstrate that there is a plausible mechanism by which adherence to IL could have affected US military personnel’s definition of a legitimate target in the observed way.