Universalizability
Ask whether the maxim of your action could become a universal law without contradiction.
How it helps
It turns a private intention into a public test of moral permissibility.
Understand in about 5 minutes
Fundamental Principles of the Metaphysic of Morals
Kant seeks the supreme principle of morality and locates it in a will that acts from duty under a law it could will for everyone.
Idea map
The book in 4 ideas
Principle of Morality Kant seeks the supreme principle that makes moral obligation unconditional.
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Good Will
The only thing conceivable as good without qualification.- Unconditional Good Other goods need it to stay good.
- Worth in Volition The willing carries the value.
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Duty
Moral worth lies in acting from duty, not from inclination.- From Duty Worth is in the motive.
- Not Inclination Pleasant motives are not moral ones.
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Categorical Imperative
The single unconditional command derived as the supreme moral principle.- Universal Law Could everyone act on this?
- End in Itself Never use people merely as tools.
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Autonomy
The will gives the moral law to itself.- Self-Legislation Bound by self-given law.
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Mental models
3 ways of thinking you can use
Humanity as an End
Treat rational beings always as ends in themselves, never merely as means.
How it helps
It guards against using people as instruments for one's own purposes.
Autonomy of the Will
A rational will is bound only by laws it could give to itself.
How it helps
It grounds moral obligation in reason rather than in external authority or reward.
Summary
The essence in plain English
The work sets out to find and establish the supreme principle of morality. Kant begins not from experience but from the ordinary moral idea that the only thing conceivable as good without qualification is a good will. Intelligence, courage, and fortune are good only when a good will directs them.
A good will is good in itself, by virtue of its volition, not by what it accomplishes. Even if it should achieve nothing, Kant says it would still shine by its own light. From this he draws his account of duty: an action's moral worth lies not in its effect or purpose but in the principle of volition from which it is done.
Kant distinguishes acting from duty from merely acting in conformity with duty. An action prompted by inclination, however agreeable, has no moral worth in his sense; worth appears when the action is done from duty alone, out of respect for the law itself rather than for any object the law might secure.
From this Kant develops the categorical imperative, the one unconditional command of practical reason. It directs the will to act only on maxims that could hold as universal laws, and equivalently to treat rational nature, in oneself and in everyone, always as an end and never merely as a means.
These formulas converge on autonomy: a rational will giving the moral law to itself. The work is an analysis rather than a chapter-by-chapter narrative, moving from common moral knowledge toward the metaphysical principle that, for Kant, makes morality binding and unconditional.
Key concepts
Terms to know
- The Good Will
- The will that is good in itself, not because of what it brings about.
- Why it matters: It is the starting point and the only thing Kant calls good without qualification.
- Duty
- Acting from respect for the moral law rather than from inclination or expected result.
- Why it matters: Kant locates an action's moral worth in its being done from duty.
- The Categorical Imperative
- The one unconditional command of reason that binds the will absolutely.
- Why it matters: It is the supreme principle Kant sets out to establish.
Selected Quotes
Short passages from the source
Nothing can possibly be conceived in the world, or even out of it, which can be called good, without qualification, except a good will.
Act only on that maxim whereby thou canst at the same time will that it should become a universal law.
So act as to treat humanity, whether in thine own person or in that of any other, in every case as an end withal, never as means only.
Source
Text used for this page
Source text: Project Gutenberg edition of Fundamental Principles of the Metaphysic of Morals by Immanuel Kant.
HTML text: https://www.gutenberg.org/cache/epub/5682/pg5682-images.html
Project Gutenberg states that this ebook is for use at no cost with almost no restrictions in the United States and most other parts of the world, subject to local law.
First published 1785; the Project Gutenberg edition uses Thomas Kingsmill Abbott's translation.