The Probability of Escalation Principle
Understanding the risk of escalation is key to discerning the just and unjust uses of limited force. Insofar as limited force is categorically different from war because it avoids the latter’s large-scale destruction and unpredictability, then holding onto a presumption against escalation from limited force to war is essential to keeping them distinct. The probability of escalation principle, introduced as part of the set of jus ad vim principles, helps to gauge the likelihood of this happening. The chapter begins by explaining what escalation is and why thinking about escalation matters for determining whether the use of limited force is just or unjust. This reveals the core of jus ad vim—the presumption against escalation maxim—which relates the strong moral penchant against making the shift from the narrow destruction of vim to the wide and unpredictable destruction of bellum. The chapter continues by exploring five archetypes of escalation—initiator, regional, on the ground, prospective, and retaliatory—along with the ethical concerns they engender to help tease out the telltale signs of when using limited force is likely to lead to escalation, as well as ways states can signal to others that escalation to war is not the intention. The chapter concludes by examining an important caveat—the conditions under which this principle might be overridden, thus making escalation to war permissible. This could be the case only in the context of humanitarian intervention to protect innocents from on-the ground escalation, and only if shaped by the principles of jus post vim.