Over the past 20 years, Steven Nadler, professor of philosophy at the University of Wisconsin at Madison, has established himself as this country’s leading authority on the philosophical thought of 17th-century Europe. He has written a major biography of Spinoza, edited scholarly works about Malebranche, been a Pulitzer finalist for “Rembrandt’s Jews,” and taken up, in “The Best of all Possible Worlds,” the arguments of Leibniz and his contemporaries about that most troubling of all theological questions: the problem of evil. Why does God allow the innocent to suffer?

Much of Nadler’s work exemplifies what the French call “haute vulgarisation,” high-level popularization. You don’t need to have aced Epistemology 101 to understand his books; you just need to pay close attention to his clear, patient exposition. In “The Philosopher, the Priest, and the Painter,” Nadler has, moreover, written his most inviting book yet.

Given its subtitle, “A Portrait of Descartes,” one would naturally expect an account of the life and thought of this key modern philosopher. But that subtitle is actually a sly pun. The great Dutch artist Frans Hals — famous for such portraits as “The Laughing Cavalier” and the bibulous old woman known as Malle Babbe — actually painted Descartes. There’s a well-known canvas in the Louvre, now generally thought to be a copy of a lost original, and a somewhat rougher, but very similar portrait in Copenhagen. This book examines the intersection of Hals, Descartes and the priest Augustijn Alsten Bloemaert, who might have brought the philosopher and painter together.

His goal, Nadler tells us, “is to restore to Hals’s portrait of Descartes some of its originality and luster by reconstructing the biographical and historical contexts of its production.” He also emphasizes that “the Haarlem artist has given us a small, intimate portrait of a great thinker. I want to do the same: a presentation of Descartes and his ideas in the form of a small, intimate portrait, a rendering of those years that culminated in some groundbreaking, philosophical doctrines and a modest but intriguing work of art.”

While Rene Descartes (1596-1650) was French by birth, he spent most of his adult life in the Netherlands. There he enjoyed the quiet and solitude he craved, but also a society relatively tolerant during a century of frequent religious and political intolerance. Nadler duly touches on many aspects of contemporary Dutch culture, including the publishing house of Elzevier, which brought out some of Descartes’s writings.

”The Philosopher, the Priest, and the Painter” by Steven Nadler. (Princeton Univ.)

Hals — obstreperous and stubborn, and a spendthrift to boot — worked mainly in Haarlem and was little known outside his country. Legend has it that he painted tipplers so often because he was one. Nadler speculates that when Descartes agreed to visit the court of Queen Christina of Sweden, his clerical friend Bloemaert commissioned Hals to create a keepsake portrait. The last chapter of “The Philosopher, the Priest, and the Painter” lays out the evidence for this, while considering other images of Descartes and the mysteries surrounding both the highly finished Louvre painting (now thought to be “after Hals”) and the rougher Copenhagen panel, generally viewed as a genuine work of the master.

Nadler’s detective work makes for fascinating reading, but where he really catches fire is in his exposition of Cartesian philosophy, especially the “Discourse on Method” and the “Meditations on First Philosophy.” These works undermined medieval scholasticism and established Descartes as the looming, Miltonic shadow of modern philosophy, a figure to learn from, argue with and rebut.

In the “Discourse of Method,” Descartes argues, in Nadler’s words, that knowledge about the world can “come only by moving beyond the confused testimony of the senses, by ignoring what is obscure and confused in the raw visual, tactile, auditory, and olfactory evidence with which we are presented to get to a scientific core that is conceptually pure and composed only of ‘clear and distinct’ elements. This is achieved through the intellect and the proper critical use of our reasoning faculties.”

In the “Meditations” — one of the most thrilling works in the history of human thought — Descartes consequently seeks to establish which, if any, of our beliefs are unassailably true. “I realized,” he wrote, “that it was necessary, once in a lifetime . . . to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last.” To this end, Descartes dares to suggest that everything people believe to be true could actually be a delusion or dream. He even imagines an all-powerful “malicious demon” whose sole purpose is to deceive us in every way. Is there, nonetheless, something that we can be sure of?

He decides that there is one fact alone we can know with certainty: “I am, I exist.” (The more celebrated formulation of this axiom appears in the “Discourse on Method”: “Cogito ergo sum” — “I think, therefore I am.”) From this epistemological starting point, Descartes gradually rebuilds the universe, beginning with a logical proof for the existence of God and of a radical distinction between mind and body. The first edition of the “Meditations” carries the tendentious subtitle “in which the existence of God and the immortality of the soul is demonstrated.”

But Descartes is as much a speculative scientist as a philosopher. In later writings, he concludes that motion is the force that creates everything in the universe. “All the variety in matter, all the diversity of its forms, depends on motion.” What’s more, he argues that “all motion is in itself rectilinear,” that bodies in motion naturally tend to move in a straight line. He even speculates about the physics of colliding entities and the conservation of energy throughout the universe. As Nadler says, Descartes insists that inquiries into the nature of the physical world or of any of its creatures “should be framed solely in terms of the way in which material particles, moving according to the laws of nature, have been ordered by impact and adhesion to produce an organism of a certain complex structure and function.” One can glimpse in these Cartesian “laws” the prefigurings of Newton’s thinking about matter, motion and inertia.

Despite the rigor of Descartes’s philosophizing, his insistence on mind-body dualism has proved especially vexatious and problematic. How are the spiritual and the corporeal connected? If, as Nadler says, you anchor the soul too intimately in the body, you risk undermining its independence and immortality. “At the other extreme, overstress its distinction from the body” and you diminish “what theologians considered the unity of human nature.” In what seems to us a surreal proposition, Descartes pointed to the pineal gland as the likely “seat of the soul.”

In the end, I don’t think “The Philosopher, the Priest, and the Painter” is entirely successful in connecting its three titular elements into an artistic unity. Nonetheless, the resulting survey of Golden Age Dutch culture, Cartesian philosophy and art connoisseurship still makes for heady and very welcome intellectual entertainment.

Dirda reviews books every Thursday for The Washington Post.

The Philosopher, the priest, and the painter

A Portrait of Descartes

By Steven Nadler.

Princeton Univ. 230 pp. $27.95