The rationalists of Module 5 had built their systems out of ideas the mind was supposed to possess from birth — innate axioms from which, by pure reason, a whole universe could be deduced. In 1690 an English physician published a long, patient book that asked a deflating question: where is the evidence? Look into a newborn, John Locke argued, and you find no innate ideas at all — no stamped-in axioms, no built-in God, nothing. The mind begins as "white paper," and everything written on it is written by experience. With that, the second great river of modern philosophy starts to flow. The empiricists hold that all our knowledge comes from the senses, and they will follow that single principle wherever it leads — even when, in Hume's hands, it leads somewhere genuinely frightening.
The three of them form an escalating argument. Locke is the moderate: he empties the mind of innate ideas but keeps almost everything else — the external world, real knowledge, God, an enduring self. Berkeley, taking Locke's "way of ideas" more seriously than Locke did, notices that if we only ever perceive our own ideas, we have no business believing in matter at all — and cheerfully abolishes it. And David Hume rides the premise to the end of the line, where it dissolves the very things the new science depended on: he shows that we cannot rationally justify cause and effect, the uniformity of nature, or even the existence of a continuing self. Empiricism, pushed to its limit, turns out to be a kind of skepticism — and it is this conclusion that will jolt Kant awake in the next module.
But this is also the century that turned philosophy outward, from the structure of the mind to the structure of society — the age that named itself the Enlightenment. The same Locke who emptied the mind also wrote the charter of modern liberalism: government rests on the consent of the governed, exists to protect natural rights, and may rightfully be overthrown when it betrays them. Across the Channel, Voltaire, Diderot, and Montesquieu turned reason into a weapon against superstition, censorship, and tyranny; Émilie du Châtelet carried Newton into French; Rousseau, the great dissenter, charged that civilization itself had corrupted a naturally good humanity, and dreamed of a republic governed by the general will. Then, in 1789, the ideas left the page. The French Revolution made philosophy a matter of life and death — and the furious argument over it, between Burke, Paine, Wollstonecraft, and Gouges, drew the map of left and right we still live on.
Mini-timeline
- 1688–89 — the Glorious Revolution; Locke returns from exile
- 1689 — Locke's Letter Concerning Toleration and Two Treatises of Government
- 1690 — Locke's Essay Concerning Human Understanding: the mind as white paper
- 1710 — Berkeley's Principles of Human Knowledge: esse est percipi
- 1734 — Voltaire's Letters on the English import Locke and Newton to France
- 1739–40 — Hume's Treatise of Human Nature
- 1748 — Montesquieu's Spirit of the Laws; Hume's first Enquiry ("Of Miracles")
- 1751 — the first volume of Diderot and d'Alembert's Encyclopédie
- 1755 — Rousseau's Discourse on Inequality; the Lisbon earthquake
- 1762 — Rousseau's Social Contract and Emile
- 1776 — the American Declaration of Independence; Hume dies
- 1779 — Hume's Dialogues Concerning Natural Religion (posthumous)
- 1789 — the French Revolution; the Declaration of the Rights of Man
- 1790–92 — Burke's Reflections; Paine's Rights of Man; Wollstonecraft's and Gouges's vindications of the rights of woman
Threads to watch
What science can know is the module's hinge: the empiricist principle that all ideas come from experience looks modest, until Hume turns it on causation and induction and shows that the foundations of natural science cannot themselves be rationally proved — the deepest crisis the thread has yet faced. Appearance and reality runs through the "way of ideas": we perceive our own perceptions, not things, and the question of what (if anything) lies behind the veil drives Locke's primary and secondary qualities, Berkeley's denial of matter, and Hume's bundle. What the self is gets two rival empiricist answers — Locke's self as continuity of memory, Hume's self as a bundle of fleeting perceptions with no owner. The just society acquires its modern foundation and its first great stress test: Locke's natural rights and government by consent, Rousseau's general will, and then the Revolution, where Burke, Paine, and Wollstonecraft fight over whether reason may remake a society from scratch. And who counts morally widens dramatically — toleration for dissenters and Jews, and the explosive demand, pressed by Wollstonecraft and Gouges, that the "rights of man" include women — while the same thinkers' complicity in slavery and racism (Locke's investments, Hume's notorious footnote) exposes how narrowly the Enlightenment first drew its circle.
Where this leads
Hume's skepticism is a loaded gun left on the table, and in Königsberg a punctual professor will pick it up. Immanuel Kant said Hume "interrupted my dogmatic slumber" — woke him from confidence in pure reason — and Module 7 is Kant's attempt to answer him: to show how the mind can have genuine knowledge of the world after all, not by reading reality passively but by actively shaping it. The two rivers, reason and experience, are about to be joined. And the Revolution's unfinished business — its glory, its Terror, and its broken promises to women and the enslaved — will haunt every political philosophy that follows.
State of the conversation
Returning after a break, or just starting here? Here is where things stand. The rationalist confidence of Module 5 has met its empiricist answer: knowledge comes from experience, not from innate ideas — and that answer, pursued honestly by Hume, has cornered itself in skepticism about cause, self, and the uniformity of nature, leaving "what science can know" in genuine crisis. Appearance and reality is now a problem about perception itself: we are each shut up with our own ideas, and Berkeley has shown how hard it is to prove there is a material world on the other side of them. The self has split into rival theories — a thread of memory, or a bundle of perceptions. Faith and reason has gone on the offensive, with toleration, deism, and Hume's quiet demolition of miracles and design. And the just society has been refounded on rights and consent — then thrown into the furnace of the French Revolution, from which the modern argument between conservative and radical emerges. Reason has conquered the public square and lost its grip on the foundations of knowledge at the same moment. Kant is waiting.