---
title: Deontological Ethics
sort: 120
section-id: ethics
description: Kant's categorical imperative, the formulas of universal law and humanity, perfect and imperfect duties, and neo-Kantian developments.
language: en
---

# Deontological Ethics

Deontological ethics holds that certain actions are intrinsically right or wrong regardless of their consequences. The term derives from the Greek *deon* (duty). Immanuel Kant (1724–1804) constructed the most influential deontological system in the history of ethics, grounding morality entirely in reason rather than sentiment or consequences.

## Kant's Moral Philosophy: Starting Points

Kant begins the *Groundwork of the Metaphysics of Morals* (1785) by identifying the only thing that is good without qualification: a **good will**.^[Kant, I. (1785). *Groundwork of the Metaphysics of Morals*. Trans. Korsgaard, Cambridge UP, 1998.] Intelligence, courage, and even happiness can be used for evil purposes. But a will that acts from duty — that acts because doing so is right, regardless of inclination or consequence — is good unconditionally.

This distinguishes acting *in accordance with* duty (which a prudent merchant might do for self-interested reasons) from acting *from* duty (the only source of genuine moral worth).

## The Categorical Imperative

Kant argues that all genuine moral requirements are *categorical* imperatives — commands that apply unconditionally, regardless of one's desires. "Pay your debts" is categorical: it applies whether or not you want to, whether or not it benefits you. By contrast, "If you want to be trusted, pay your debts" is a *hypothetical* imperative, binding only if you have the relevant desire.

Kant offers three principal formulations of the categorical imperative, claiming they are equivalent:

### Formula of Universal Law (FUL)
> "Act only according to that maxim whereby you can at the same time will that it should become a universal law."

To test whether an action is permissible, extract the maxim (underlying principle) of the action and ask: could I consistently will that everyone act on this maxim? The classic example is lying promises. My maxim: "When in financial difficulty, I will make a false promise to repay a loan." If universalised, the institution of promising collapses — no one would believe promises. The maxim is self-defeating when universalised.

### Formula of Humanity (FH)
> "Act so that you treat humanity, whether in your own person or in that of another, always as an end and never as a means only."

Persons have *dignity* — a value beyond all price. Using someone merely as an instrument for your purposes violates their status as a rational, self-legislating agent. This formula generates more intuitive verdicts than FUL in many cases and grounds a robust conception of human rights.

### Formula of the Kingdom of Ends (FKE)
> "Act according to maxims of a universally legislating member of a merely possible kingdom of ends."

The moral community is a hypothetical kingdom of rational agents who legislate universal laws for themselves and for all. Each person is both subject to and author of the moral law.

## Perfect and Imperfect Duties

Kant distinguishes **perfect duties** (negative, admitting no exceptions) from **imperfect duties** (positive, allowing latitude in how they are fulfilled).

- *Perfect duties*: Do not murder. Do not lie. Do not make false promises. These admit no exceptions.
- *Imperfect duties*: Develop your talents. Help others in need. We must pursue these ends, but have discretion in how.

## The Formula of Universal Law: Applications

Kant tests four cases:

1. **Suicide to escape suffering** — The maxim of self-destruction from self-love contradicts itself when universalised (life-preserving instinct cannot simultaneously mandate destroying life).
2. **False promises** — Universalised, this destroys the institution of promising.
3. **Neglecting one's talents** — Although we can consistently will a world where all neglect their talents, we cannot *rationally* will such a world as members who might need others' developed capacities.
4. **Refusing to aid others** — We cannot rationally will a world with no mutual aid, since we might need it ourselves.

## Objections to Kantian Ethics

### The Problem of Conflicting Duties
What if telling the truth would lead to murder? The notorious example: a murderer asks you where your friend is hiding. Kant's strict application of FUL seems to require telling the truth.^[Kant, I. (1797). "On a Supposed Right to Lie from Philanthropy."] Most critics find this conclusion intolerable. Defenders argue Kant was wrong to apply his own theory in this case.

### The Formalism Objection (Hegel)
Hegel objected that the categorical imperative is empty — too formal to generate determinate moral content. Almost any maxim can be made consistent with FUL through reformulation.^[Hegel, G.W.F. (1821). *Philosophy of Right*, §135.]

### The Rigorism Objection
The absolute prohibition on lying, even to prevent serious harm, seems morally obtuse. A moral theory that ignores consequences entirely cannot be adequate.

### The Humanity Formula and Its Scope
Does FH extend to animals? Kant seems to deny that animals have dignity (since they lack rationality), but this generates counterintuitive implications about the permissibility of animal cruelty.

## Neo-Kantian Developments

**Christine Korsgaard** grounds Kantian ethics in the structure of reflective self-consciousness. When we act, we implicitly endorse a principle. Practical identity — the source of all our obligations — commits us to valuing humanity as an end.^[Korsgaard, C. (1996). *Sources of Normativity*. Cambridge University Press.]

**Thomas Scanlon's contractualism**: An act is wrong if its performance under the circumstances would be disallowed by any set of principles that no one could reasonably reject.^[Scanlon, T.M. (1998). *What We Owe to Each Other*. Harvard University Press.] This grounds moral requirements in what we owe to each other as persons — a broadly Kantian spirit without the metaphysical apparatus.

**W.D. Ross** introduced the concept of *prima facie* duties — duties that are binding unless overridden by stronger competing duties in a given situation. Fidelity, gratitude, non-maleficence, beneficence, and justice are among them. This pluralist deontology avoids the single-minded rigour of Kant while preserving the idea that some actions have moral weight independent of consequences.^[Ross, W.D. (1930). *The Right and the Good*. Oxford University Press.]

## Further Reading

- Korsgaard, C. (1996). *Creating the Kingdom of Ends*. Cambridge University Press.
- O'Neill, O. (1989). *Constructions of Reason*. Cambridge University Press.
- Herman, B. (1993). *The Practice of Moral Judgment*. Harvard University Press.
