Scientists were once happy to be known as natural philosophers. The title implied not merely that they studied nature but that they thought about it in such a way as to discern its hidden laws. They weren’t concerned only with the how of things but with the why. The beautiful line of Virgil, “Happy is he who can recognize the causes of things,” epitomized the endeavor. Causation in all its forms, from the collisions of solid bodies on earth to the remote arrangements of the First Cause beyond the empyrean, underlay natural laws. Goethe’s Faust, the mythic prototype of the philosopher-scientist, was driven to despair, as well as near-damnation, by his passion to know “what holds the world together in its deepest core.” But Faust represents the end of an ancient tradition; for all his knowledge, he’s tormented by the world’s ultimate unknowability. And that bafflement “scorches his heart.”

Is nature finally unintelligible? Even more disturbing, is nature intelligible in itself but beyond the power of humans to comprehend? These and other questions form the theme of Peter Dear’s excellent new book, “The Intelligibility of Nature: How Science Makes Sense of the World” (University of Chicago Press, 233 pages, $27.50). Mr. Dear, a historian of science at Cornell, provides a succinct history of modern science from the 17th century to the present by drawing on two complementary but conflicting aspects of the scientific method. The first involves the search for “intelligibility,” or the truth about nature; the second concerns “instrumentality,” or the practical uses scientists make of their discoveries. As he demonstrates, in lucid prose and wellchosen illustrations, these two aspects aren’t quite compatible, and yet, both have proved essential to the advancement of science.

The criterion of intelligibility sounds obvious but isn’t. As Mr. Dear shows, even Newton was harshly criticized, by the Dutch mathematician Christiaan Huyghens, among others, for his inability to explain the phenomenon of gravitation. He could describe the force and derive laws and inferences from it but he couldn’t account for it in a satisfactorily philosophical manner. The criticism stung Newton because he agreed with Huyghens.The seemingly insuperable problem was “action at a distance.” How could one object — whether a heavenly body or the earth beneath an apple tree — influence another without some sustaining medium through which gravity could act? Mr. Dear cites a letter in which Newton protests, “Pray do not ascribe that notion to me, for the cause of gravity is what I do not pretend to know and therefore would take more time to consider of it.”

In an introduction, six detailed chapters, and a final summation, Mr. Dear examines the tension between theory and practice in such sciences as celestial mechanics, taxonomy, chemistry, biology, physics, and quantum theory.The portraits of individual scientists, from Newton, Boyle, and Faraday to Einstein and Bohr, are vivid and pithy; he has a good ear for the apt quote that lets us hear their voices. His chapter on taxonomy, which frankly I was dreading, proves unexpectedly fascinating. How we classify the world, and the things it contains, betrays our deepest presuppositions. Do we order the overwhelming profusion of plants and animals by their similarities or by their differences? Or do we attempt, like some earlier taxonomists, to arrange them as they might appear in the mind of God? This is a seemingly dry but fundamental subject made lively in the telling. And it too is philosophical in essence, as Mr. Dear neatly points out:

Classification was not just cataloguing, the imposition of arbitrarily selected ordering principles; it was not mere ‘natural history’ in the usual sense of the straightforward description of nature’s contents. Eighteenthcentury taxonomists generally aimed at being natural philosophers who could provide the conceptual understanding that would raise the status of their work and establish it as philosophically meaningful, not simply as useful.

He is especially good on the work of Linnaeus, as well as on such lesser-known figures as Antoine Laurent de Jussieu, the late-18th-century French botanist whose revolutionary work, appropriately published in 1789, attempted to classify plants according to observed natural order yet based on the assumption that “the universe, God’s creation, is a panoply of realized possibilities, and the possibilities represented by terrestrial vegetable creation could therefore be expected to find actualization in real plants found somewhere on the earth.” For Jussieu, unlike Linnaeus, creation was not static but a “continuum” in which undiscovered forms could be predicted. And in his superb later chapter on Darwin, Mr. Dear astutely notes the irony that Darwin’s success in formulating his theories owed something to the fact that he was quite a poor taxonomist; his incompetence freed him from rigid preconceptions.

In his final chapter, on quantum physics, Mr. Dear illumines the fundamental divergence between the demands of intelligibility and the lures of instrumentality in the dramatic figures of Einstein and Bohr. Einstein’s benign public persona couldn’t quite conceal his Faustian side; he was passionately stubborn in insisting that the world was, and must be, intelligible in the end. As he remarked, “the most incomprehensible thing about the world is that it is comprehensible.” Against this, Bohr, a kind of wellmeaning Mephistopheles, championed the probabilistic claims of quantum mechanics. Mr. Dear summarizes the contrast well: “Einstein wanted physics to speak about a world that existed independently of the human observer.” By contrast, Bohr “wanted quantum mechanics to be seen as a necessary implication of the way the world works. Rather than being a mere theory, then, quantum mechanics was to be seen as a discovery. And what quantum mechanics could not know, human beings could not know.” In other words, because quantum mechanics exhibited demonstrable effects — because it was highly instrumental — Bohr argued for its truth. But Einstein, who valued only “theories of principle” rather than working hypotheses, remained adamantly opposed. The universe could not, for him, be reduced to a “cloud of probabilities.” It had to be intelligible.

Not all of Mr. Dear’s summaries convince. His discussion of the Einstein-Podolsky-Rosen “thought-experiment,” known usually as EPR, omits any mention of quantum entanglement, the process — which Einstein called “spooky” — whereby two subatomic particles affect each other’s position or momentum, when measured, despite the distance that separates them. And in his conclusion he offers a gratuitous nod, completely out of the blue, to the specious trendiness that views Western science as merely one “ideology” among others. It’s hard to believe that Mr. Dear accepts such nonsense; indeed, the thrust of his book suggests quite the opposite. If science doesn’t entail the search for verifiable truth, however flawed, then we’re no better off than poor Faust, scorched by the unattainable.

eormsby@nysun.com