John Rawls argued that we should separate two questions: whether a practice (like punishment or promising) is justified, and whether a particular act fits the rules of that practice. This helped clarify how rule-based reasoning can matter even when single acts look outcome-improving. The act-versus-rule contrast became a key reference point for later debates about deontological rules and exceptions.
J. J. C. Smart defended “extreme” (act) utilitarianism and criticized “restricted” (rule) utilitarianism as unstable. He argued that either it collapses into act utilitarianism (if rules allow exceptions whenever outcomes are better) or it becomes “rule worship” (following rules even when clearly worse). These objections became a standard challenge for any theory that tries to be rule-guided but still sensitive to outcomes.
David Lyons developed a detailed critique of rule utilitarianism, arguing that if rules are specified finely enough to handle every exception, the view effectively turns into act utilitarianism. This “collapse” style argument influenced later thinking about whether rule-like moral constraints can be principled rather than ad hoc. It set a template for parallel worries about rule-like forms of deontology.
Philippa Foot used a runaway “tram” case while discussing abortion and the doctrine of double effect. The case highlighted tensions between outcome-driven reasoning and constraints that limit what may be done to people. It became a starting point for later analytic work that tested whether deontological constraints are best understood as firm rules or as more context-sensitive judgments about particular acts.
Robert Nozick argued that individual rights act as “side-constraints,” limiting what may be done to people even to achieve better overall outcomes. This way of framing deontological constraints supported a rule-like reading (constraints as general limits) while also raising questions about how to treat borderline cases and tradeoffs. It became influential across ethics and political philosophy as a clear statement of constraint-based morality.
Judith Jarvis Thomson’s paper compared cases like diverting a trolley with cases like killing one healthy person to save five. By holding outcomes constant while changing how harm is done, she pushed philosophers to ask whether deontological constraints are strict rules (no killing) or whether permissibility turns on finer features of particular acts (like intention or using a person as a means). Her work helped make act-focused vs rule-focused interpretations of deontology a live analytic debate.
Through the late 1970s, trolley cases and adjacent examples intensified discussion about whether doing harm is morally worse than allowing harm, even when outcomes are similar. This distinction mattered for act-focused deontology (which can treat the structure of a particular action as decisive) and for rule-focused deontology (which must decide whether to encode such distinctions into general rules). It helped shift the debate from slogans (“never kill”) toward more fine-grained analysis of action types.
Thomson’s later discussion helped popularize the label “the trolley problem” for a family of cases that test moral constraints. These cases became standard tools for probing whether deontological restrictions work as exceptionless rules or as judgments sensitive to features like intention, agency, and using a person as a means. The growing “trolley” literature provided common ground for analytic debates about act versus rule deontology.
In influential work on Kant’s Formula of Humanity, Christine Korsgaard argued that rational agency gives rise to obligations that apply to all agents. This line of thought helped revive interest in deontology grounded in general principles about persons, not just intuitive verdicts about cases. In the act-versus-rule debate, it bolstered approaches that aim to justify stable, shareable rules rather than relying mainly on case-by-case moral perception.
By the late 1980s, analytic ethics increasingly used explicit labels to distinguish act-focused and rule-focused forms of deontology. This helped separate debates about what makes actions right (features of particular acts versus conformity to rules) from debates about how we should deliberate (rules of thumb versus direct judgment). The clearer taxonomy made it easier to see recurring problems: exceptions, conflicts of duties, and how much outcomes may override constraints.
Warren Quinn analyzed the doctrine of double effect and argued that some morally important differences concern how victims are involved in an agent’s plan (often described as “direct” versus “indirect” agency). This supported an act-sensitive approach: two acts with similar consequences can differ morally because of their internal structure. At the same time, it created pressure on rule-like formulations to explain which features should be built into general constraints.
Across 1950–1990, the act-versus-rule deontology debate increasingly centered on a shared question: how can non-consequentialist constraints guide action without either becoming rigid “rule worship” or dissolving into outcome-maximization? Work on trolley cases, double effect, and side-constraints pushed deontologists to specify what kinds of exceptions (if any) are allowed and why. By around 1990, the field had a stable set of test cases and argumentative moves that shaped later discussions of threshold deontology, rights, and permissible harm.
Act versus rule deontology debate in analytic ethics (1950–1990)