Philosophy › Reason, experience & Enlightenment
Immanuel Kant
1724–1804· Philosopher· Reality, mind & God
Well documentedSolid records, texts or physical evidence.
Prussian philosopher who argued that the mind actively shapes experience and that morality rests on reason, not feelings or consequences.
See it on the Philosophy map →The idea
The idea: we never meet the world raw; the mind supplies space, time and cause and effect, so we know things as they appear, not as they are in themselves. Roused by Hume's doubts, he combined empiricism with rationalism and wrote three Critiques (1781, 1788, 1790), on knowledge, morality and beauty. He never traveled far from Königsberg, where neighbors supposedly set their clocks by his daily walk. Main objection: if things in themselves are unknowable, how can he say they exist?
Why it matters
Nearly all later Western philosophy starts from Kant, building on him or reacting against him; his idea of human dignity underlies modern human-rights thinking.
Legacy and sources
His works, letters, notes and students' lecture transcripts fill the Academy Edition, begun in 1900. Early biographers who knew him recorded his famously regular routine.
Still debated
How his racial hierarchies, taught in his geography and anthropology lectures, square with his universal ethics is now actively debated by scholars.
Inside this (3)
Connections (8)
▸Anselm's ontological argument was rejected by Immanuel KantWell documented
The connection
Anselm argued that God, 'that than which nothing greater can be conceived,' must exist, since existing is greater than not existing. Kant replied that 'being is obviously not a real predicate': existence adds nothing to a concept. A hundred real thalers (coins) contain no more than a hundred imagined ones, so no definition can prove existence.
When and how
Kant's Critique of Pure Reason (1781), in the Transcendental Dialectic, aimed mainly at Descartes's and Leibniz's versions; Kant also coined the name 'ontological proof.'
How we know
The Critique's section 'On the Impossibility of an Ontological Proof of God's Existence'; later logicians like Frege and Russell formalized his point.
Debates and open questions
Whether Kant refuted Anselm's own version, and whether modern modal versions, such as Alvin Plantinga's (1974) or Kurt Gödel's, escape his objection.
▸David Hume interrupted the "dogmatic slumber" of Immanuel KantWell documented
The connection
Hume argued we never see causes necessarily producing effects, only one event regularly following another; causation is a habit of mind. If so, science's laws rest on custom. Kant took the challenge seriously and answered that cause and effect is a category the mind brings to experience, so it holds necessarily for everything we can experience.
When and how
Königsberg, probably in the late 1760s or early 1770s; Kant read Hume in German translation and told the story in his Prolegomena (1783).
How we know
Kant wrote: 'the remembrance of David Hume was the very thing that many years ago first interrupted my dogmatic slumber.'
Debates and open questions
When the awakening happened, and which Hume texts Kant knew; he read little English, so he likely knew Hume's Treatise only through excerpts and summaries.
▸British empiricism was synthesized with rationalism by Immanuel KantWell documented
The connection
Empiricists (Locke, Berkeley, Hume) said all knowledge comes from experience; rationalists (Descartes, Leibniz) said reason alone can grasp reality. Kant took both halves: 'all our knowledge begins with experience,' but 'it does not follow that it all arises out of experience'; the mind supplies the forms that organize it.
When and how
Königsberg, in the Critique of Pure Reason (1781, revised 1787); Kant was trained in the Leibniz-Wolff rationalism then dominant in German universities.
How we know
The Critique says outright that Leibniz 'intellectualized' appearances while Locke 'sensualized' concepts, and positions itself between them.
Debates and open questions
Whether 'empiricists versus rationalists' is a tidy story that later historians, partly following Kant himself, imposed on more varied thinkers.
▸Jean-Jacques Rousseau influenced Immanuel KantWell documented
The connection
Rousseau taught Kant to honor ordinary people's moral worth, not just learning. His idea that freedom is obeying a law you give yourself became Kant's 'autonomy,' and the general will foreshadows Kant's test of universal law. Kant wrote, 'Rousseau has set me right... I learn to honor human beings.'
When and how
Königsberg, mid-1760s, after Kant read Émile and The Social Contract (both 1762); the remark is scribbled in his own copy of his 1764 Observations on the Beautiful and Sublime.
How we know
Kant's handwritten notes, published after his death; early biographers report that Rousseau's portrait was the only picture in his study.
Debates and open questions
The story that reading Émile made him skip his daily walk is probably embellished; how far autonomy derives from Rousseau is debated.
▸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.
▸Immanuel Kant formulated The categorical imperativeWell documented
The connection
Kant sought a moral law binding on any rational being, resting on neither desires nor outcomes. Only a good will, acting from duty, is good without qualification. He gave the principle several forms: universal law, treating humanity as an end, and a 'kingdom of ends,' a community where everyone is both lawmaker and subject.
When and how
Königsberg, in the Groundwork of the Metaphysics of Morals (Riga, 1785), developed in the Critique of Practical Reason (1788) and Metaphysics of Morals (1797).
How we know
The texts themselves; students' notes of his ethics lectures, from the 1760s to the 1790s, show the idea taking shape.
Debates and open questions
Whether the several formulations are really equivalent, as Kant claimed, or express different moral ideas that can conflict.
▸Immanuel Kant named "dare to know" the motto of The EnlightenmentWell documented
The connection
Kant defined enlightenment as humanity's 'emergence from its self-incurred immaturity,' the inability to use one's own understanding without another's guidance. Its motto, borrowed from the Roman poet Horace: 'Sapere aude! Dare to know!' He urged free public use of reason in print, while still obeying in one's official role.
When and how
Königsberg, December 1784, in the Berlinische Monatsschrift, answering a pastor's footnote question; Moses Mendelssohn published his own answer the same year.
How we know
The essay 'An Answer to the Question: What Is Enlightenment?' survives and is the most quoted definition of the movement.
Debates and open questions
How radical it was, since it praised Frederick the Great's 'argue, but obey'; historians also doubt the Enlightenment had one core idea at all.
▸Immanuel Kant answered "disinterested pleasure" to What is beauty? The question of aestheticsWell documented
The connection
Kant said a judgment of beauty rests on 'disinterested' pleasure: delight in an object's form without wanting to own, use or consume it, as when admiring a facade without thinking about its rents. Yet we speak as if everyone should agree. He distinguished the merely agreeable, the beautiful and the sublime, such as storms or mountains that overwhelm the senses.
When and how
Königsberg, in the Critique of the Power of Judgment (1790), Kant's third Critique, which bridges his theories of nature and freedom.
How we know
The text itself, and its direct influence on Schiller, the Romantics and 20th-century formalist critics such as Clement Greenberg.
Debates and open questions
Whether taste can be universal if it rests on feeling; sociologist Pierre Bourdieu (1979) argued that 'disinterested' taste is really a marker of social class.