Kant crossed two distinctions:
| A priori (independent of experience) | A posteriori (from experience) | |
|---|---|---|
| Analytic (predicate contained in subject) | “All bachelors are unmarried” | — (empty) |
| Synthetic (adds new information) | “7 + 5 = 12”, “every event has a cause” | “The cat is on the mat” |
Hume’s Fork allowed only the top-left and bottom-right boxes. Kant claimed the bottom-left box is full — and that mathematics, geometry, and the foundations of physics live there. Explaining how is the whole project of the Critique of Pure Reason: such judgments are possible because they express the conditions any experience must meet.
The critics
- Friedrich Nietzsche (Beyond Good and Evil §11): Kant’s answer — “by means of a faculty” — explains nothing, like Molière’s doctor attributing opium’s effect to its “dormitive virtue.” Better to ask why we need such judgments to be believed.
- Frege argued arithmetic is analytic (reducible to logic), shrinking Kant’s box.
- Non-Euclidean geometry and relativity showed physical space need not be Euclidean.
- W. V. O. Quine (“Two Dogmas of Empiricism”, 1951) attacked the analytic/synthetic distinction itself.
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related by shared connections
Critique of Pure Reason
Kant’s masterwork, asking what reason can know without experience — and answering that it can know the forms of all possible experience, but nothing beyond.
Prolegomena to Any Future Metaphysics
Kant’s short, clearer restatement of the first Critique, where he credits Hume with waking him from his dogmatic slumber.
David Hume
The great Scottish sceptic who showed that causation, the self, and induction cannot be justified by reason — and that reason is, and ought only to be, the slave of the passions.
Continental Rationalism
The seventeenth-century conviction that reason alone, unaided by the senses, can reach certain knowledge of the deepest truths.
Rationalism vs. Empiricism
The great quarrel of early modern philosophy — does knowledge come from reason or from experience? Kant tried to end it.
The Enlightenment
The eighteenth-century movement that put reason, science, tolerance and individual liberty at the centre of human affairs — “Sapere aude!”