Specifying the Proportionality Test and the Standard of Due Precaution: Problems of Prognostic Assessment in Determining the Meaning of “May Be Expected” and “Anticipated”

This chapter addresses the challenging legal and operational issues raised by the proportionality requirement to assess the legality of collateral damage. Specifically, the chapter engages closely with the relevant text of Articles 51(5)(b) and 57(2)(b) of the First Additional Protocol to the Geneva Conventions. The chapter first asks what makes an attack that unavoidably includes incidental loss of civilian lives or civilian property an “indiscriminate attack” under Article 51(5)(b). In more concrete terms, it asks how the formula for collateral damage—“excessive in relation to the concrete and direct military advantage anticipated”—may be operationalized. The chapter then moves to an analysis of the rule of precautions in Article 57(2)(b), with special emphasis on understanding how the military operator should navigate this rule in light of battlefield realities. The chapter then poses how these rules may be best understood under the regime of international criminal law.