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What if doing right begins where getting what you want ends?
In The Critique of Practical Reason, Immanuel Kant asks whether reason can tell us what we ought to do, without appealing to wishes or rewards. His answer places moral law at the center of human freedom. A personal rule must face a demanding test: could it hold as a law for every rational being?
Kant then confronts a harder question. Duty asks us to deserve happiness, but it does not promise that happiness will follow. His argument leads from the categorical imperative to the highest good, and to the place of hope, immortality, and belief in God within his moral philosophy. The challenge is to understand what can guide us when desire cannot.
What you’ll discover
- A test for action Explore the categorical imperative, which asks whether your personal rules could become universal laws.
- Freedom through moral law Follow Kant's argument that freedom means giving yourself the law, not simply following desire.
- Duty without a reward Consider why Kant grounds morality in reason rather than pleasure, happiness, or natural feeling.
- The motive of respect Examine what moves a person to act from duty when inclination pulls another way.
- Happiness and the highest good Trace Kant's effort to bring virtue and happiness together without making happiness morality's foundation.
Who will love it
This book suits readers who like to ask what duty is, where freedom comes from and why honesty matters even when it costs everything. It rewards anyone who enjoys clear moral arguments and vivid examples.
What’s inside
The key ideas, in the 15-minute summary
- Reason asks what we must do
- Moral commands have no if
- Your rule must hold for everyone
- Duty reveals that we are free
- Respect gives an act moral worth
- Natural causes do not erase responsibility
- The highest good joins virtue and happiness
- Moral education trains judgment through examples
- Test your rules and your motives
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The Critique of Practical Reason
by Immanuel Kant · 1788
A boy hears of an honest man pressed to slander Anne Boleyn, and Kant asks what duty really is.
Challenging2–5 hours to read2 languages
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In short
What makes an act good? Is it the result, the feeling behind it, or something else entirely?
The Critique of Practical Reason at a glance
- Reading time
- About 4 h3 h 10 min fast, 4 h 45 min slow
- Length
- 56,800 words
- Library level
- Challenging long sentences, a rich vocabulary
- First published
- 1788by Immanuel Kant
Reading time at 238 words a minute (fast 300, slow 200). How long the classics take to read · Updated
From the 15-minute summary · Key idea 1
Reason can guide the will by itself
Kant calls the book a critique of practical reason, not of pure practical reason. His aim is to show that pure reason really can be practical, meaning it can decide what we will without help from outside.
In his first critique, reason was warned against claiming too much. Here the worry is reversed. Reason tied to experience and desire is the one that overreaches, because it tries to rule the will on its own terms.
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- 15-minute summary
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Details
- First published
- 1788
- Language
- English
- Level
- Challenging
Cite this edition
Kant, Immanuel. The Critique of Practical Reason. Library of Alexandria, 2026, libraryofalexandria.com/products/the-critique-of-practical-reason.
Kant, I. (2026). The critique of practical reason. Library of Alexandria. https://libraryofalexandria.com/products/the-critique-of-practical-reason (Original work published 1788)
Kant, Immanuel. The Critique of Practical Reason. Library of Alexandria, 2026. https://libraryofalexandria.com/products/the-critique-of-practical-reason.
@book{kant2026critique,
author = {Kant, Immanuel},
title = {The Critique of Practical Reason},
publisher = {Library of Alexandria},
year = {2026},
url = {https://libraryofalexandria.com/products/the-critique-of-practical-reason},
note = {First published 1788}
}
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What is The Critique of Practical Reason about?
It asks how reason can guide the will without help from desire or reward. Kant argues that the moral law is a fact of reason, that it reveals human freedom, and that it leads to hope for the highest good.
What is the categorical imperative in this book?
It is a command that binds without any if. Kant states it as acting so that your maxim could serve as a principle of universal legislation, meaning a rule that everyone could follow.
What is the difference between a maxim and a law?
A maxim is a personal rule of one person's will. A law is valid for the will of every rational being. Kant tests a maxim by asking whether it could hold universally without defeating itself.
The author
Immanuel Kant
1724–1804 · German philosopher
Immanuel Kant was a German philosopher born in Königsberg, Prussia, in 1724. He lived there until his death in 1804 and taught at its university. He wrote Critique of Pure Reason in 1781, Critique of Practical Reason in 1788, Critique of Judgement in 1790, and Perpetual Peace in 1795.
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