Radical and moderate Enlightenment

The last lesson’s caution now pays off: the Enlightenment was internally divided. The historian Jonathan Israel has made influential a distinction that captures the split — between a moderate mainstream and a radical wing. They shared the appeal to reason but disagreed, fundamentally, about how far reason was allowed to go.

The moderate Enlightenment — the mainstream — sought to reconcile reason with religious faith, with tradition, and with existing authority. Its aim was reform, not demolition: purify religion of superstition, temper monarchy with law and rights, let reason and revelation coexist. Its representatives are the ones we have met — Locke, Voltaire’s deism, Montesquieu’s constitutionalism, and, in his own careful way, Kant.

The radical Enlightenment pushed reason to conclusions the moderates would not accept: to naturalistic, egalitarian, and secular ends. One nature with no supernatural remainder — no miracles, no immaterial soul standing outside the causal order. Materialism about mind and world. Democracy rather than reformed monarchy. And full freedom of thought, unbounded by the compromises that let religion keep its authority. Where the moderate renovates, the radical rebuilds from the ground.

The radicals’ subterranean source was Baruch Spinoza (1632–1677). His formula Deus sive Natura — “God, or Nature,” the two words naming one and the same thing — collapses the Creator into the single, self-sufficient natural order. There is exactly one substance; everything is a mode of it; nothing stands outside or above nature. See Ethics I, Prop. 15, where all things are in God, and Spinoza’s Ethics I, Prop. 29 on a nature governed throughout by necessity.

Two radical figures carried this forward in France. The later Diderot — the same editor of the Encyclopédie — moved in his mature works toward outright materialism, imagining a self-organizing nature with no need of God. And Baron d’Holbach went furthest: his System of Nature (1770) was a frank profession of atheism and materialism, arguing that everything, mind included, is matter in motion, and that religion is a human invention born of fear and ignorance.

Now a voice that fits neither wing cleanly — the great dissenter from within, Jean-Jacques Rousseau (1712–1778). Half inside the Enlightenment (a contributor to the Encyclopédie, a friend then enemy of the philosophes), half against it, Rousseau turned the movement’s central faith — in progress — into a question.

In his Discourse on the Sciences and Arts (1750), Rousseau argued the scandalous thesis that the progress of the arts and sciences had corrupted, not improved, us — refining our manners while rotting our morals, breeding vanity, luxury, and dependence. In the Discourse on Inequality (1755) he added that civilization itself breeds inequality: private property and society drag humanity out of a free natural condition into chains. The Enlightenment’s proudest achievement, culture, is arraigned as the source of our misery.

Yet Rousseau was no mere pessimist; in The Social Contract (1762) he offered a cure. Genuine freedom is not doing as you please but obedience to the general will (volonté générale) — the shared will of a people aimed at the common good, which each citizen, as a member of the sovereign body, gives to himself. Under the general will one obeys only laws one has, in this sense, authored — so one remains free while obeying. Rousseau’s paradox: true liberty is self-given law.

Step back and see the shape of the whole unit. The Enlightenment contains a live tension: reason as reform (moderate) versus reason as subversion (radical), and progress celebrated versus progress questioned from within (Rousseau). This is not a flaw to tidy away — it is the movement’s inner life. And it sets up what comes next: Kant’s balancing act (Unit 3), which tries to hold reform, freedom, and order together; and the later critics of Enlightenment reason (Unit 6), who ask whether reason itself can go wrong.