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German Idealism · Treatise
Critique of Pure Reason
by Kant · The Judge of Reason · Enlightenment, 1724-1804
Kant's complete critique asks how experience, science, metaphysics, and reason's illusions are possible.
- Brutal
- ~15 hr 45 min read
- 8 chapter guides
- Public domain
Start reading · Read the SECTION II. Of Time. guide free
Before the text
Editor's Prelude
Reason Before Its Own Tribunal
A falling stone has a cause. A triangle has properties that no new observation can overturn. Yet the same mind that confidently judges these things asks questions it cannot settle: whether the world had a beginning, whether we are free, whether there is a God. Kant asks what gives reason its authority—and why its demand for answers can lead it into conflict with itself.
The Critique first appeared in 1781 and was substantially revised in 1787. Kant describes the work as a tribunal before which reason must examine its own claims. Mathematics and natural science make knowledge possible without settling every question that matters to a human being. He wants to understand their certainty while testing the attempts to turn the soul, the whole universe or God into objects of speculative knowledge.
The argument moves through definitions, examples, tables and opposing proofs. Sensibility gives us objects in intuition; understanding thinks them through concepts; reason seeks the completeness that individual experiences cannot supply. Familiar words such as experience, idea and freedom acquire exact jobs in this architecture. The distinction between things as they appear and things as they may be in themselves matters at every turn: a limit on what we can know also changes what we can responsibly affirm or deny.
The opening pages
PART FIRST. TRANSCENDENTAL ÆSTHETIC.
TRANSCENDENTAL DOCTRINE OF ELEMENTS.
§ 1. Introductory.
In whatsoever mode, or by whatsoever means, our knowledge may relate to objects, it is at least quite clear, that the only manner in which it immediately relates to them, is by means of an intuition. To this as the indispensable groundwork, all thought points. But an intuition can take place only in so far as the object is given to us. This, again, is only possible, to man at least, on condition that the object affect the mind in a certain manner. The capacity for receiving representations (receptivity) through the mode in which we are affected by objects, is called sensibility. By means of sensibility, therefore, objects are given to us, and it alone furnishes us with intuitions; by the understanding they are thought, and from it arise conceptions. But all thought must directly, or indirectly, by means of certain signs, relate ultimately to intuitions; consequently, with us, to sensibility, because in no other way can an object be given to us.
The effect of an object upon the faculty of representation, so far as we are affected by the said object, is sensation. That sort of intuition which relates to an object by means of sensation, is called an empirical intuition. The undetermined object of an empirical intuition, is called phænomenon. That which in the phænomenon corresponds to the sensation, I term its matter; but that which effects that the content of the phænomenon can be arranged under certain relations, I call its form. But that in which our sensations are merely arranged, and by which they are susceptible of assuming a certain form, cannot be itself sensation. It is then, the matter of all phænomena that is given to us à posteriori; the form must lie ready à priori for them in the mind and consequently can be regarded separately from all sensation.
I call all representations pure, in the transcendental meaning of the word, wherein nothing is met with that belongs to sensation. And accordingly we find existing in the mind à priori, the pure form of sensuous intuitions in general, in which all the manifold content of the phænomenal world is arranged and viewed under certain relations. This pure form of sensibility I shall call pure intuition. Thus, if I take away from our representation of a body, all that the understanding thinks as belonging to it, as substance, force, divisibility, &c., and also whatever belongs to sensation, as impenetrability, hardness, colour, &c.; yet there is still something left us from this empirical intuition, namely, extension and shape. These belong to pure intuition, which exists à priori in the mind, as a mere form of sensibility, and without any real object of the senses or any sensation.
Chapter guides · 8
SECTION II. Of Time.
The Form of Change
Kant argues that time is a condition of how things appear, then confines that claim to the objects of possible experience.
Time before particular events
We recognize events as simultaneous or successive only by already representing time. Kant therefore treats time as a necessary form of intuition, rather than a concept assembled from observations. Different times are parts of one time; limits mark portions within it. Change becomes intelligible through this form, since incompatible states can belong to the same thing at different times.
Real for experience
Time belongs immediately to our inner sense and, through our representations, conditions appearances generally. Kant calls it empirically real: every object of experience is subject to it. Its transcendental ideality means that we cannot transfer this condition of our sensibility to things as they are in themselves. The distinction leaves temporal experience valid while withholding a claim about an independently existing time.
Appearance and knowledge
The general remarks extend this distinction to sensibility as a whole. Even a perfectly clear perception would give us an appearance under our forms of intuition, rather than knowledge of the thing in itself. Kant closes by identifying the requirement for synthetic judgments a priori: a concept must be joined to an intuition. For human cognition, that intuition is sensuous, so such judgments reach objects through the conditions of possible experience.
Section III. Of the Pure Conceptions of the Understanding, or Categories § 6
An Inventory of Understanding
The logical forms of judgment supply Kant’s categories, while older appeals to unity, truth and perfection receive a different explanation.
From judgment to categories
Kant uses the functions of judgment to identify the pure concepts through which understanding unites a manifold of intuition. The twelve categories fall under quantity, quality, relation and modality. His objection to Aristotle is that a collection assembled without a common principle mixes unlike kinds of concepts and cannot establish its own completeness. Further concepts can be derived from the categories, but Kant postpones their full enumeration.
Relations within the table
The first two classes concern objects of intuition; the latter two concern their existence and relations. Each class has three members. Its third category arises through a connection of the first two that requires an act of understanding: totality, for example, is plurality considered as unity. Community also receives a particular explanation through the way the members of a disjunctive judgment jointly constitute a whole.
Unity, truth and perfection
The scholastic claim that every being is one, true and good might seem to demand additional categories. Kant instead treats these terms as logical requirements for cognition. Qualitative unity concerns the coherence of a concept; truth concerns the consequences that can be drawn from it; perfection concerns their completeness. The section ends by concluding that the table is complete without them: unity, truth and perfection are just the three categories of quantity, used as logical rules for knowledge agreeing with itself.
Section II. Of the Supreme Principle of all Synthetical Judgments
How a Judgment Reaches an Object
A synthetic judgment needs more than consistency: Kant grounds its objective validity in the conditions that make experience possible.
Section II. Of Transcendental Ideas
Reason’s Demand for Completeness
Reason seeks the whole series of conditions, producing necessary ideas for which experience cannot furnish an adequate object.
Section III. Of the Interest of Reason in these Self-contradictions
The Attractions of Opposing Answers
Practical hopes and the wish for a complete explanation make metaphysical convictions compelling, without settling the dispute between them.
Section IX. Of the Empirical Use of the Regulative Principle of Reason with regard to the Cosmological Ideas
How Inquiry Can Continue
Kant answers the antinomies: the world is never given to us as a finished whole, and natural causes and free action can both hold, because the same act can be viewed as an event in nature and as the work of reason.
Section VI. Of the Impossibility of a Physico-Theological Proof
What Design Cannot Establish
The world’s order encourages the search for a wise author, but Kant denies that it proves an absolutely necessary creator.
Section IV. The Discipline of Pure Reason in Relation to Proofs
The Discipline of Proof
Kant requires a justified ground for transcendental proofs and rejects victories gained through unexamined alternatives.
Questions readers ask
- How long does it take to read Critique of Pure Reason?
- About 15 hr 45 min in total.
- How difficult is Critique of Pure Reason?
- Brutal. A long treatise; about 16 hours of reading.
- Which translation is this?
- The J. M. D. Meiklejohn translation from the German, first published in 1781. The text follows Critique of Pure Reason, translated by J. M. D. Meiklejohn (London: George Bell and Sons, 1890; Bohn's Philosophical Library).
- Can I read Critique of Pure Reason for free?
- Critique of Pure Reason is part of Nexus Premium, so reading it needs an account and a Premium subscription. The opening above and two chapter guides on this page are free to read.
- How many chapter guides are there?
- 8 chapter guides, written by the Nexus editors. Two open in full here; the rest show their opening line.
About Kant
Immanuel Kant spent nearly his entire life in Königsberg, teaching and writing with remarkable regularity. His mature work attempted to explain the powers and limits of reason, while grounding morality in freedom, duty, and human autonomy.
“What must the mind contribute for experience to be possible?”
Kant changes the center of philosophy by asking not just what we know, but how knowing is possible.
Source text: public domain. Chapter guides: original Nexus writing. Critique of Pure Reason is part of The Nexus Archive, guided Quests through the great works.