---
title: Deontological Ethics
section-id: ethics
sort: 120
author: Prof. James Okafor
created: 2026-02-21 09:00
modified: 2026-03-29 11:00
language: en
description: Kantian ethics, the categorical imperative, and duty-based approaches to morality.
---

# Deontological Ethics

Deontological theories hold that certain actions are intrinsically right or wrong, regardless of their consequences. The rightness of an action is determined by its conformity to a rule or duty, not by the outcomes it produces. The most developed and influential deontological theory is Kant’s.

## Kant’s Ethics

Immanuel Kant held that the moral worth of an action lies not in its consequences but in the **will** that performs it. An action has moral worth only if it is done from a sense of duty (*Pflicht*).

Kant identified a single supreme principle of morality—the **categorical imperative**—which he stated in several formulations.

### The Universal Law Formulation
‘Act only according to that maxim whereby you can at the same time will that it should become a universal law.’

When contemplating an action, identify the maxim (principle) on which you are acting. Ask: could this maxim be universalised without contradiction? Lying to get out of a difficulty fails this test: if everyone lied whenever convenient, the practice of truth-telling would collapse, and lying would be pointless—we cannot coherently universalise it.

### The Humanity Formulation
‘Act in such a way that you treat humanity, whether in your own person or in the person of any other, never merely as a means to an end, but always at the same time as an end.’

Persons have a dignity that precludes their being treated merely as instruments for others’ purposes. This formulation captures the intuition behind the transplant objection to consequentialism: killing one person to benefit five treats the victim merely as a means.

### The Kingdom of Ends
Kant’s third formulation asks us to act as if we were legislators in a kingdom of ends: a community of rational agents who treat each other as ends in themselves. We should act only on principles that could be endorsed by all rational agents as members of such a community.

## Kant’s Deontological Commitments

For Kant, the moral law applies absolutely. Lying is wrong even if lying would save an innocent person’s life. Kant’s rigidity here has troubled many readers. If a murderer asks where your friend is hiding, must you tell the truth?

Kant maintained that you must not lie, though you need not volunteer information. Critics find this result unacceptable—a theory that prohibits lying to murderers cannot be correct. Defenders argue that the correct formulation of the duty is more nuanced or that context allows for responses that are not strictly lies.

## Rights and Constraints

Deontological theories are naturally suited to grounding **rights**: claims individuals have that constrain how they may be treated, regardless of aggregate welfare. Robert Nozick argued that individuals have rights—to life, liberty, and property—that function as ‘side constraints’ on the pursuit of good outcomes. Rights cannot be violated even to produce a better distribution of rights overall.

Nozick’s position generates a **historical theory of justice**: distributions are just if they arise from just initial holdings by just transfers, regardless of their pattern. This leads to strong conclusions against redistributive taxation, which Nozick likens to forced labour.

## The Problem of Moral Conflicts

Deontological theories face the problem of moral conflicts: what happens when two duties conflict? W.D. Ross proposed the notion of **prima facie duties**: duties that hold ‘other things being equal’ but may be overridden by weightier duties in particular cases. We have prima facie duties of beneficence, non-maleficence, fidelity, gratitude, justice, and self-improvement. Determining which duty takes precedence in a conflict requires judgement, not a mechanical rule.

Ross’s approach is more flexible than Kant’s but gives up the idea of a single supreme principle from which all duties can be derived.

## Contemporary Deontology

Contemporary deontologists have developed more sophisticated accounts of rights, constraints, and duties. Frances Kamm and Judith Jarvis Thomson have explored the moral significance of the distinction between doing harm and allowing harm, and of the direction of harm (harming as a side effect vs as a means). This work illuminates why the trolley problem—diverting a trolley to kill one and save five—seems morally different from pushing someone off a bridge to achieve the same outcome.

## Summary

- Deontological theories ground rightness in conformity to duties or rules, not consequences
- Kant’s categorical imperative has three main formulations: universal law, humanity, and kingdom of ends
- Rights function as constraints that cannot be overridden for aggregate benefit
- Prima facie duties (Ross) allow for moral conflicts to be resolved by judgment
- Contemporary deontologists explore the doing/allowing distinction and the structure of constraints
