Scott Russell Sanders is the author of “Earth Works: Selected Essays”, among other books.

Freedoms that Americans too easily take for granted — freedom of speech, press, assembly and religion — are the legacy of a relatively few daring thinkers in 18th-century Europe who risked their own freedom to voice forbidden ideas. None was more daring, none challenged a wider range of beliefs and institutions, than French philosopher Denis Diderot, the subject of this engrossing biography by Andrew S. Curran, professor of humanities at Wesleyan University.

During a life that spanned most of the century, 1713 to 1784, Diderot wrote or edited a prodigious amount of literature, much of it published posthumously. In “Diderot and the Art of Thinking Freely,” a narrative sustained with appealing clarity and energy, Curran reveals how this son of devoutly Catholic parents came to question the existence of God and how, from that radical premise, Diderot went on to question the legitimacy of the established church, the monarchy, sexual mores, aristocratic privileges, the slave trade and European colonization.

Not surprisingly, some of his writings were burned, and others were placed on the Catholic Index of Prohibited Books. Accused of heresy for his first major publication, “Pensées philosophiques” (“Philosophical Thoughts”), he spent a few months in prison. To protect himself and his manuscripts from the authorities, he often hid out in shadier sections of Paris. At times, he considered leaving France for a more tolerant haven elsewhere. The wonder is that he escaped execution and survived to die a natural death at the age of 70 while reaching across his dining table for another helping of stewed cherries.

Diderot managed to escape more severe penalties through the intervention of sympathizers in high places, including Madame de Pompadour, mistress to Louis XV, and through his own wiles, including a willingness to lie when asked by the police if he was the author of certain inflammatory books. While he valued honesty as highly as did any Enlightenment sage, he saw no point in giving truthful answers to the censors. Along with other dissidents, he could be denounced at any moment by guardians of the status quo — gendarmes, priests, Sorbonne theologians, rival intellectuals, the Paris Parliament, every “regulator of dangerous beliefs” up to and including the pope and king.

He dodged and battled the censors for a quarter-century as lead editor of the “Encyclopédie,” a massive project that eventually filled 17 volumes containing some 74,000 articles, several thousand of which Diderot wrote himself. The full title of this monumental work, in English, is “Encyclopedia or Reasoned Dictionary of Science, Arts and Crafts.” Curran calls it “The Enlightenment Bible,” an apt label for a work that champions observation and reason, rather than revelation and tradition, as the most reliable sources of knowledge. Behind it lay the influence of John Locke’s epistemology and Isaac Newton’s dazzling demonstration of the scientific method.

Of the 150 or so contributors to the “Encyclopedia,” none was more willing to question the scriptures or flout received opinion than Diderot. In one article, for example, he casts doubt on the existence of the soul, and in another, Curran observes, he “puts forward the perilous idea that the real origin of political authority stems from the people, and that this political body not only has the inalienable right to delegate this power, but to take it back as well.” This idea was indeed perilous, as Thomas Jefferson, John Adams and other delegates to the Continental Congress well knew when they defied the British crown and Parliament by adopting the Declaration of Independence on July 4, 1776, four years after publication of the final volume of the “Encyclopedia.”

The keepers of church and state were understandably dismayed by this challenge to their authority, none more so than Louis XV. He considered throwing Diderot and a co-editor into the Bastille but chose instead to order that all unpublished “Encyclopedia” articles be confiscated. By the time police showed up at the print shop, however, Diderot had managed to spirit away the manuscripts, and he eventually saw them all through to publication.

When he concluded his heroic, quarter-century effort on this revolutionary publication, Diderot regretted having sacrificed so much of his life to this enterprise and having been forced to make so many concessions to the censors. “What Diderot did not fully realize,” Curran writes, “was that he had carried the ideas of the Enlightenment forward in a way that no person, not Voltaire, and certainly not Rousseau, had done before.” Those ideas included freedom of thought and expression, in all domains, including religion; a vision of democracy based on popular sovereignty; and a vision of justice based on human equality.

While at work on the “Encyclopedia,” Diderot continued writing subversive plays, novels, satires and histories, many of which he chose not to publish. Instead, late in life, intending for these secret manuscripts to be published after his death, he arranged to have three copies made, one for his daughter, one for his literary executor and one for Catherine the Great of Russia, his longtime patron.

Curran examines several of these “improbably modern books and essays,” including “D’Alembert’s Dream,” a novel that offers an evolutionary view of human origins, foreshadowing Darwin, and two fictional dialogues, “Rameau’s Nephew” and “Jacques the Fatalist,” which debate the meaning of life and morality in the material universe revealed by science. In these and other writings, Diderot condemned economic inequality in ways that anticipate Marx, and he anticipated Freud by diagnosing sexual repression — a malady he avoided by indulging in a series of mistresses. His book on acting influenced Konstantin Stanislavsky, and his art criticism drew the attention of Catherine the Great, who commissioned him to acquire paintings and sculptures for her collection in the Hermitage.

“To become familiar with the range of Diderot’s work is to be stupefied,” Curran remarks. Indeed, readers of this biography are likely to be impressed by the scope of Diderot’s thought and by his courage, as he risked persecution to ask and answer taboo questions, thereby making it easier, and safer, for us to do the same.

Diderot and the Art of Thinking Freely

By Andrew S. Curran

Other. 520 pp. $28.95