Technologies of Decision Support and Proportionality in International Humanitarian Law

Abstract What does proportionality reasoning mean for decision support in international humanitarian law (ihl)? We first consider contemporary ihl commentaries on proportionality as an analogue form of decision support through a paradigmatic example. Over time, proportionality in ihl has changed from being a rule-specific space for discretionary decision making to a much broader compromise-seeking within boundaries marked by law. Today, proportionality is a master norm in ihl, remaking rules by stealth and enabling the accommodation of novel master technologies as lawful. Artificial Intelligence (ai) support for military decision making is one such master technology that resonates particularly well with the inner structure of proportionality thinking: both build on cost-benefit analysis and engender the quantification of the world through data collection. We analyse how cost-benefit analysis and digitalization and algorithmic processing intersect in the U.S. legal context, to then proliferate into U.S. warfare and decision support systems, and onwards into ihl.