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Critique of Pure Reason
1781· Book or text· Knowledge, logic & science
Well documentedSolid records, texts or physical evidence.
Kant's 1781 masterwork asking what reason can know without experience, and answering: only the structure of possible experience itself.
See it on the Philosophy map →The idea
The idea: some knowledge is both informative and certain, such as '7+5=12' or 'every event has a cause,' because the mind imposes it on all experience. Kant called this his Copernican revolution: objects conform to our minds, not the reverse. 'Thoughts without content are empty, intuitions without concepts are blind.' But reason overreaches when it tries to prove God, the soul or the world's beginning, landing in contradictions. Main objection: non-Euclidean geometry and relativity undercut his claim that space must be Euclidean.
Why it matters
It set modern philosophy's agenda: what are the limits of knowledge, and how much of the world we experience is built by our own minds?
Where it comes from
Published in Riga in May 1781 and heavily revised in 1787; scholars cite the editions as A and B. Kant's shorter Prolegomena (1783) restated it after confused reviews.
Still debated
What exactly changed between the 1781 and 1787 editions, especially in the key 'transcendental deduction,' and whether they present different views.
Connections (3)
▸Immanuel Kant wrote Critique of Pure ReasonWell documented
The connection
After his 1770 inaugural dissertation on the limits of sense and reason, Kant published almost nothing for eleven years, his 'silent decade,' wrestling with how concepts can apply to objects. He then wrote the Critique, he said, in four or five months, and revised it heavily in 1787 after reviewers misread it.
When and how
Königsberg, 1770–1781; published in Riga by Johann Friedrich Hartknoch in May 1781, when Kant was 57; second edition 1787.
How we know
His 1772 letter to Marcus Herz outlines the problem; a 1783 letter to Moses Mendelssohn describes the rushed writing; both editions survive.
Debates and open questions
Why he rewrote the core argument in 1787; Schopenhauer and Heidegger preferred the first edition, and scholars still compare the two versions.
▸Critique of Pure Reason redrew the limits of What can we know?Mostly agreed
The connection
Kant asked, in his own words, 'What can I know?' His answer split knowledge in two: we can know the structure of all possible experience with certainty, because the mind supplies it, but never things in themselves, nor God, the soul or freedom by pure reason. 'I had to deny knowledge to make room for faith.'
When and how
Critique of Pure Reason, 1781 and 1787; the three questions 'What can I know? What ought I to do? What may I hope?' appear near its end.
How sure are we?
The text states the questions and limits explicitly; later thinkers, from Hegel to the logical positivists, framed their views for or against those limits.
Debates and open questions
Whether things in themselves are separate objects or the same objects viewed another way, and whether modern physics undermines his account of space and time.
▸Critique of Pure Reason set off the German idealism of G. W. F. HegelWell documented
The connection
Kant left an unknowable 'thing in itself' beyond experience. Fichte dropped it, making the self the source of the world; Schelling and Hegel followed. Hegel argued that to draw a limit to knowledge you must already see past it, so reason can know reality as a whole, and he turned Kant's contradictions of reason into the engine of thought.
When and how
Jena, 1790s–1807, where Fichte, Schelling and Hegel all taught; Hegel's Faith and Knowledge (1802) attacked Kant directly.
How we know
Hegel's explicit criticisms of Kant in Faith and Knowledge, the Phenomenology and his lectures; he likened testing knowledge before knowing to refusing to enter water before learning to swim.
Debates and open questions
Whether German idealism completed Kant or misread him; Kant himself publicly disowned Fichte's version of his philosophy in 1799.