Get started

WorkImmanuel Kant

The Critique of Pure Reason

Eleven years in the writing and unreadable on arrival in 1781: the book that asked whether reason can know anything beyond experience, and reset European philosophy on the answer.

by Immanuel Kant2,529 passages held

  • German, the original language
  • English, a translation held here, and your language
Sign in or subscribe to discuss this work See it in context
Original title
Kritik der reinen Vernunft
First published
(aged 57)
Original language
German
Form
Treatise

Report a rights issue

Overview

For eleven years Kant published almost nothing. He had taken a chair at Königsberg in 1770 and then gone quiet, and colleagues wondered whether the promised book would ever come. It came in 1781, over eight hundred pages long, and its first readers could not follow it. The question it answers is whether metaphysics is possible at all — whether reason can know anything beyond experience, as it had always claimed to, about God, the soul, the beginning of the world. Kant's answer reverses the terms. Instead of asking how our knowledge conforms to objects, he asks what objects must be like to be knowable by minds structured as ours are: space and time are not things we find but the forms in which anything can be given to us, and the categories of the understanding are conditions we bring, not features we discover. He called it a revolution on the model of Copernicus. It follows that the old metaphysics had been reaching past the only world it could know, and that God, freedom and immortality can be neither proved nor disproved. The first notice, a Göttingen review that Garve wrote and Feder cut down, called the whole thing warmed-over Berkeley, an idealism that dissolved the real world. Kant was stung enough to write the Prolegomena in 1783 to be understood, and in 1787 to reissue the book with its central deduction rewritten and a refutation of idealism built in. Within a decade it had swallowed German philosophy whole.

Key concepts

What does Kant mean by 'synthetic a priori' knowledge?

It is knowledge that is necessary and universal (a priori), yet genuinely extends what we know rather than merely unpacking a definition (synthetic) — 'seven plus five equals twelve,' or 'every event has a cause.' That such knowledge exists is not in doubt; how it is possible is the single problem the whole Critique sets itself to solve.

What are the 'categories' of the understanding?

The categories are the pure concepts — cause and effect, substance, unity, necessity and the rest, twelve in all — that the mind brings to every experience rather than reads off the world. They are conditions that make objective experience possible. Distinct from space and time, which are the forms of intuition, the categories are the forms of thought.

What is the 'transcendental deduction'?

It is the book's hardest and most crucial argument: the proof that the categories must apply to every object we can experience, because without them no unified, ordered experience would be possible at all. Its difficulty and importance are why Kant tore it up and rewrote it for the 1787 second edition, along with a new refutation of idealism.

What is the thing-in-itself, and how do phenomena differ?

The thing-in-itself is the object as it is in its own right, apart from the forms of space, time and the categories our minds impose. Phenomena are objects as they appear under those forms — the only objects we can ever know. Kant keeps the thing-in-itself to mark that appearances are appearances of something, while insisting it stays unknowable.

What are the 'antinomies' of pure reason?

The antinomies are pairs of contradictory conclusions that reason can prove with equal force once it argues about the world as a whole — that it has a beginning in time and that it does not, that everything is determined and that there is freedom. They expose reason overreaching its limits, and Kant dissolves them by separating appearances from things-in-themselves.

What does 'transcendental idealism' mean?

It is the doctrine that space, time and the categories are contributed by the knowing subject, so we know objects only as appearances, never as things-in-themselves. It is idealism about the form of experience, not — as the hostile Göttingen review charged — a Berkeleyan denial that anything real exists outside us. Kant added a refutation of idealism to make the point.

Themes of the book

What this book returns to, gathered into themes and ordered by how much of the text each one occupies.

The Copernican Turn

Rather than ask how our knowledge conforms to objects, what if we ask what objects must be like to be known by minds built as ours are? The reversal Kant staked everything on.

Knowledge does not mould itself to things; things, to be known at all, must submit to the forms a mind brings to them. Kant called the inversion a revolution on Copernicus's model, and it decides the book's central question — whether metaphysics is possible — by relocating necessity and universality from the world into the knower. Synthetic a priori judgements, true and yet informative, become the thing to be explained, and the explanation is that we supply their form. Every later argument in the book is a consequence of this single move.

  • metaphysics
  • epistemology
  • cognition
  • subjectivity
  • reason
  • methodology
  • a priori
  • synthesis
  • knowledge

Enter a dialogue

Space, Time, and the Understanding

Are space and time features we discover in the world, or the very frame in which anything can be given to us at all? On the answer hangs what we may and may not know.

Space and time are not things we find but the forms of our sensibility — the conditions under which any object can appear — and the categories of the understanding are further conditions we bring, not properties we read off nature. Experience is the joint work of what the senses receive and what the mind imposes, so its necessary structure can be known in advance. The price is exact and Kant pays it without flinching: we know appearances, never things as they are in themselves.

  • space
  • time
  • intuition
  • perception
  • understanding
  • synthesis
  • experience

Enter a dialogue

What Reason May Not Know

If a mind can know only what experience gives it, what becomes of reason's oldest claims — God, the soul, the beginning of the world?

Reaching past all possible experience, the old metaphysics had argued for a first cause, an immortal soul, a bounded or boundless world — and Kant watches each proof collapse into contradiction the moment reason strays beyond where intuition can follow. God, freedom and immortality can therefore be neither proved nor disproved by theory; the questions are real but permanently undecidable for knowledge. Far from mere demolition, the result clears room the second Critique will fill on practical grounds, letting the moralist believe what the theorist may not claim to know.

  • limits of knowledge
  • theology
  • reality
  • existence
  • causality
  • reason
  • nature

Enter a dialogue

Within this work

passages held
2,529
distinct concepts
1,041
by passages held, corpus-wide
#7

What this book thinks together

Every arc around the wheel is one concept in this book. A ribbon joins two the text reaches for together, and its width is how many of its passages hold both. Strongest: metaphysics with reason.
Concept co-occurrence, strongest first 8 concepts, joined by 24 pairings. 1,691 shared passages in all. 76 weaker pairings reach beyond these concepts and are not drawn.
ConceptPaired conceptShared passages
metaphysicsreason171
logicmetaphysics146
causalitymetaphysics114
cognitionperception114
limits of knowledgemetaphysics113
logicreason102
limits of knowledgereason98
epistemologylogic92
cognitionlogic75
causalitylogic69
causalityreason69
metaphysicsperception58
epistemologymetaphysics53
cognitionepistemology50
epistemologyreason48
cognitionreason42
epistemologyperception41
logicperception39
causalityperception38
cognitionmetaphysics36
epistemologylimits of knowledge36
limits of knowledgelogic35
limits of knowledgeperception35
causalitycognition17

Works held

The author's work in order, this book marked in place. Your-language title first, the original beneath it where the two differ; side chips show which full texts are held.

  1. 1764 Inquiry Concerning the Distinctness of the Principles of Natural Theology and Morality (Untersuchung über die Deutlichkeit der Grundsätze der natürlichen Theologie und der Moral)

    Kant's runner-up entry in the Berlin Academy's prize contest, and the sharpest of the pre-critical essays: it already sets philosophy's method against mathematics', the problem the first Critique would finally resolve.

     DE
  2. 1764 Observations on the Feeling of the Beautiful and Sublime (Beobachtungen über das Gefühl des Schönen und Erhabenen)

    The popular essay of Kant's pre-critical years, twenty-six years before the Critique of Judgement gave taste a rigorous grounding; its remarks on race and sex now drive much of the scholarship on him.

     DE
  3. 1766 Dreams of a Spirit-Seer, Elucidated by Dreams of Metaphysics (Träume eines Geistersehers, erläutert durch Träume der Metaphysik)

    The anonymous, ironic book of 1766 in which Kant's faith in speculative metaphysics visibly collapses — the clearing of the ground that the first Critique, fifteen years later, would build on.

     DE
  4. 1781 The Critique of Pure Reason (Kritik der reinen Vernunft) you are here DEEN
  5. 1784 An Answer to the Question: What Is Enlightenment? (Beantwortung der Frage: Was ist Aufklärung?)

    The most quoted thing Kant wrote, and among the shortest: a 1784 magazine answer to a question a Berlin pastor had left hanging, and the defining slogan of the German Enlightenment.

     DE
  6. 1784 Idea for a Universal History with a Cosmopolitan Purpose (Idee zu einer allgemeinen Geschichte in weltbürgerlicher Absicht)

    The essay where Kant first treats history as more than chronicle — nine propositions arguing it has a hidden rational shape; the seed of Perpetual Peace, and a device Hegel later took over.

     DE
  7. 1785 Fundamental Principles of the Metaphysic of Morals (Grundlegung zur Metaphysik der Sitten)

    The short, deliberately preliminary book that isolates the categorical imperative before building anything on it; three years later the Critique of Practical Reason would give the same moral law its fuller grounding.

     DEEN
  8. 1786 What Does It Mean to Orient Oneself in Thinking? (Was heißt: sich im Denken orientieren?)

    An intervention in the pantheism controversy that split the German Enlightenment: written months after Mendelssohn's death, it stakes out a rational faith between dogmatic proof and Jacobi's leap.

     DE
  9. 1788 The Critique of Practical Reason (Kritik der praktischen Vernunft)

    The second of the three Critiques, and Kant's reply to those who doubted the Groundwork's freedom; it introduces the fact of reason and the postulates of God and immortality.

     DEEN
  10. 1793 Religion within the Boundaries of Mere Reason (Die Religion innerhalb der Grenzen der bloßen Vernunft)

    The book that got Kant ordered to stop writing on religion: four essays, from 1793, rebuilding Christian doctrine on reason and consigning revelation and clergy to what Kant called counterfeit service.

     DE
  11. 1795 Perpetual Peace: A Philosophical Sketch (Zum ewigen Frieden: Ein philosophischer Entwurf)

    The late essay whose plan for a league of free states reached the twentieth century intact; Kant, past seventy, wrote it as Prussia pulled out of the war against revolutionary France.

     DE
  12. 1797 Einleitung in die Rechtslehre

    The framing section of the Doctrine of Right, the legal half of Kant's 1797 Metaphysics of Morals; it defines a right through freedom alone and ties every right to a power to coerce.

     DE
  13. 1798 Von der Macht des Gemüts, durch den bloßen Vorsatz seiner krankhaften Gefühle Meister zu sein

    The third part of Kant's late Conflict of the Faculties (1798), written as a reply to the physician Hufeland — a philosopher's dietetics, and his most personal page on governing the body through the mind.

     DE
  14. 1803 Lectures on Pedagogy (Über Pädagogik)

    One of the last books to appear under Kant's name (1803), though his editor Rink built it from lecture notes; the fullest record of Kant on education, and of his debt to Rousseau.

     DE
  15. Critique of Judgement

    The book the Romantics and the German Idealists built on: Kant's 1790 account of beauty and of purpose in nature, written to bridge the gulf that had opened between his first two Critiques.

     DEEN
  16. Prolegomena to Any Future Metaphysics

    Written to salvage the Critique of Pure Reason after its baffled reception, this shorter 1783 restatement runs the same argument in reverse, and became most readers' first encounter with Kant.

     DEEN
  17. The Metaphysical Elements of Ethics (Die Metaphysik der Sitten)

    Long read as a mere appendix to the Groundwork, this ethical half of the 1797 Metaphysics of Morals is where Kant spells out the duties of virtue; later Kantians recovered it as his theory of character.

     DEEN
Sign in or subscribe to discuss this work

— or open another of their works