In his Tractatus Theologico-Politicus, a work of politics and religion that is too often overlooked nowadays, Baruch Spinoza offered one of the earliest and most powerful arguments for a separation of church and state. Upon its release in 1670, the book was denounced as “godless” and “full of abominations.” It was promptly banned.

Philosophy professor Stephen Nadler tells the story of the book that scandalized early modern Europe—and laid the groundwork for modern republican, anticlerical, and anti-sectarian movements—in his readable A Book Forged in Hell (Princeton). “To the extent that we are committed to the ideal of a secular society free of ecclesiastic influence and governed by toleration, liberty, and a conception of civic virtue,” writes Nadler, “we are the heirs of Spinoza’s scandalous treatise.” —Katherine Mangu-Ward