Spinoza assembled his own tribe of like-minded individuals, most of them freethinking liberal Protestants. Israel and another eminent Spinoza biographer, Steven Nadler, have shed light on these key relationships. Franciscus van den Enden, Spinoza’s Latin teacher and sometime landlord, was a former Jesuit who drew up a plan for a utopian society in New Netherland, the Dutch colony that became New York; he ended up being hanged by the French for helping to hatch a plot against Louis XIV. Lodewijk Meyer, a leading figure in Dutch literary life, is believed to be the author of an anonymous book, published in 1666, that caused a huge scandal by arguing that the Bible should be analyzed critically and scientifically. Johannes Bouwmeester co-founded a club for freethinkers with the defiant name Nil Volentibus Arduum (“Nothing Is Difficult for the Willing”).

Such figures helped to create what Israel calls the Radical Enlightenment, a tradition of political and religious thought that would transform the modern world. Democratic ideas that were punishable by imprisonment in the sixteen-sixties became the watchwords of the American and French Revolutions a century later. Today, the propositions about God and the Bible that sent Adriaan Koerbagh to prison are taken for granted by secular people around the world, especially in the Netherlands, where fifty-seven per cent of those fifteen years and older say they have no religion.

Many thinkers shared the ideas of the Radical Enlightenment, but it was Spinoza who forced Europe to reckon with them, by rooting them in a new philosophical system of formidable scope and rigor. When Spinoza writes that democracy is “of all forms of government the most natural, and the most consonant with individual liberty,” and that the best antidote to superstition is the study of science, “since the less men know of nature the more easily can they coin fictitious ideas,” he isn’t simply stating opinions. The title page of his magnum opus, the “Ethics,” promises that his ideas will be “ordine geometrico demonstrata,” “demonstrated in the manner of geometry,” and, like Euclid, he presents his arguments in the form of numbered axioms and propositions. Once you accept Spinoza’s basic assumptions about God and the universe, his political and social ideas are supposed to be as self-evident as the Pythagorean theorem.

At the center of Spinoza’s thought is a new way of understanding God. Indeed, his God was so different from the one worshipped in churches and synagogues that almost everyone who read him believed he was an atheist. But Spinoza indignantly rejected the charge of atheism, and nowhere in the “Ethics” does he deny the existence of God. What he denies is that God exists as a being or intelligence separate from the rest of the universe, as he is conceived of in Judaism and Christianity. Spinoza’s argument is disconcertingly simple. God is “a being absolutely infinite,” and the idea of infinity “involves no negation”: it would be contradictory to say that there is some quality an infinite being does not possess or some space it does not occupy. It is therefore impossible for God to be somewhere—up in Heaven, perhaps—but not here, where we are. If God exists, then he must be absolutely everywhere; not even our own bodies and minds can be separate from him. As Proposition XV of the “Ethics” famously states, “Whatsoever is, is in God, and without God nothing can be, or be conceived.”

This idea is known as pantheism, from the Greek for “all” and “God.” One way of looking at pantheism is that it brings us closer to God than conventional religious belief ever could; in the nineteenth century, Romantic writers considered Spinoza a “God-intoxicated man.” But, if there is no difference or distance between God and the rest of the universe, then he cannot do any of the things that we ordinarily think of God as doing: hearing prayers, working miracles, creating the world with a “Let there be light.” Really, there is no compelling reason to call Spinoza’s infinite substance God in the first place. We might as well call it Being, or Everything, or Nature. In Part IV of the “Ethics,” Spinoza refers to “the eternal and infinite Being, which we call God or Nature”—in Latin, Deus sive natura.

In closing the gap between humanity, God, and nature, Spinoza also does away with any space for free will. The infinite substance that is God appears to be constantly changing, yet always in accordance with what Spinoza calls “the necessity of his nature,” or what a scientist would call natural laws. The ancient Greek engineer Archimedes said that with a lever and a place to stand he could move the Earth, but in Spinoza’s universe there is no place outside nature where we can stand in order to exert force on it, since we ourselves are part of nature.

This might sound like a fatalistic view of the world, and for later thinkers the idea that the universe is nothing but a mechanism in motion, constantly changing but never going anywhere, was a recipe for nihilism and despair. But one of the things that draws people to Spinoza, and makes him perhaps the most beloved philosopher since Socrates, is his confident equanimity. He argues that the highest happiness of which human beings are capable is seeing the universe “under the aspect of eternity,” which means understanding that everything is as it must be. When he writes that “blessedness is nothing else but the contentment of spirit, which arises from the intuitive knowledge of God,” he might sound like a mystic, but for him knowing God is not a supernatural experience but a rational one. It simply means knowing “the actions which follow from the necessity of his nature,” in the same way that knowing the law of gravity allows us to understand why an object thrown with a certain force will follow a certain trajectory.

It is because Spinoza sees true understanding as the key to happiness that he insists on freedom of thought. When religious authorities tell people what to believe, they make it harder to achieve a correct idea of God, and thus block the road to blessedness. Spinoza advocated for democratic government because he thought that it was more likely than monarchy or aristocracy to preserve libertas philosophandi, and thus to make it possible for human beings to become happy. As he writes in the “Tractatus,” “The basis and aim of a democracy is to avoid the desires as irrational, and to bring men as far as possible under the control of reason, so that they may live in peace and harmony.”

Clearly, this is not a description of the society we live in today. Liberal democracy as we know it rests on a certain intuition about equality: if all people are created equal, then no one has a monopoly on truth or wisdom, so no one has the right to dictate to others without their consent. This makes democracy a recipe for constant disagreement, as individuals and groups argue their way to some kind of acceptable consensus.

This was not the way Spinoza thought about freedom. He believed that there was one truth, which he understood and most people did not, and his experiences with religion and politics left him with no illusions about the wisdom of the crowd. Buruma, who excels at setting a rather unworldly man in the public life of his time, describes how, in 1672, a mob in The Hague lynched Johan and Cornelis de Witt, brothers who had led the Netherlands’ liberal regime during what is now remembered as the Dutch Golden Age. “One man tried to bite off Cornelis’s testicles,” Buruma writes. “Women danced in a frenzy after wrapping themselves in the slippery intestines.” Spinoza, who was living “only a short walk away,” wept at the news and had to be physically restrained from going to the site of the massacre to set up a placard reading “Ultimi barbarorum,” “the lowest of barbarians.”

As a freethinker who had run afoul of both Judaism and Christianity, Spinoza knew that bigotry and fanaticism weren’t just imposed on the people; they were also imposed by the people. Part of the reason he never met a fate like Koerbagh’s is that he took care not to provoke the crowd. Koerbagh wrote his books in Dutch so that anyone could read them, but Spinoza stuck to Latin, the language of the learned élite. In the preface to the “Tractatus,” he declares that he is writing only for philosophers and discourages “the multitude, and those of like passions with the multitude,” from reading the book: “I would rather that they should utterly neglect it, than that they should misinterpret it after their wont.”

When the “Tractatus” provoked a hostile reaction anyway, Spinoza decided not to publish anything else. He also turned down an offer to become a professor at the University of Heidelberg, on the ground that holding an official position would expose him to even more attacks. All of his work, including the “Ethics,” was left in manuscript form for his friends to print after his death. He died relatively young, in 1677, at the age of forty-four, of a lung condition that may have been linked to glass particles inhaled while grinding lenses.

To Leo Strauss, one of Spinoza’s most influential twentieth-century interpreters, this caution put him in a long philosophical tradition. In 1941, Strauss, who had fled Nazi Germany and was teaching with other Jewish refugees at the New School, in New York, published an essay titled “Persecution and the Art of Writing,” in which he argued that the repression and censorship then reigning in totalitarian Europe represented a return to the historical norm. Ever since Socrates was put to death by the Athenian assembly, philosophers had known that it was dangerous to speak the whole truth in public. When it comes to politics and religion, Strauss wrote, “a man of independent thought can utter his views in public and remain unharmed, provided he moves with circumspection. He can even utter them in print without incurring any danger, provided he is capable of writing between the lines.”

Strauss considered Spinoza a classic example of this “esoteric” style of writing, noting that the “Caute” on his ring referred to “the caution that the philosopher needs in his intercourse with non-philosophers.” If, as Buruma warns, we are entering an era in which “freedom of thought is under threat from secular theologies,” Spinoza may be the role model we need: a thinker who spoke the most outrageous truths he knew, and still managed to die in his bed. ♦