The Accountability Threshold: Thomas Aquinas’ Doctrine of Double Effect

Thomas Aquinas formulated the doctrine of double effect to address a perennial moral problem: what happens when a well-intentioned action produces harmful side effects? Under certain conditions, Aquinas argued, the harm can be permissible — provided it is foreseen but not intended.

AI systems produce unintended consequences constantly. A hiring algorithm optimised for productivity may systematically disadvantage certain groups. A content recommendation engine designed for engagement may amplify misinformation. The harm is foreseeable, yet no one “intends” it.

This episode asks where the accountability threshold lies — and whether Aquinas’ medieval framework can help us navigate the moral complexity of systems whose consequences outrun their designers’ intentions.