first heard about Galileo’s discovery of four moons orbiting Jupiter in 1610, as a student at the Jesuit college at La Flèche. Although Descartes was only thirteen or fourteen when this astonishing news reached his outpost in the French countryside, he understood at once the profound effects such a discovery could have on philosophy and physics. The very scope of those effects, however, also reinforced for him two growing suspicions: that although philosophy “has been cultivated for many centuries by the most excellent minds,” as he later wrote, “there is still no point in it which is not disputed and hence doubtful”; and that as “for the other sciences, in so far as they borrow their principles from philosophy I decided that nothing solid could have been built upon such shaky foundations.” The only rational approach to this appalling and ongoing state of ignorance, he concluded, was to begin again, from the beginning—“to demolish everything completely and start right again from the foundations,” and to do so by seeking “no knowledge other than that which could be found in myself or else in the great book of the world.”
The World, in fact, was what he called his first attempt to explain all of physics. As was often the case with Descartes when he produced a work of physics, he simultaneously produced a companion work on how a reconception of physics would necessitate a new interpretation of man’s role in it—a new physiology. This work he called Treatise on Man. He completed both in 1633, a year after Galileo released his own attempt at a new physics, Dialogue Concerning the Two Chief World Systems. But before his two volumes could reach publication, Descartes heard that the Roman Catholic Church had condemned Galileo because the Dialogue posited a sun-centered universe. Since his own two essays did the same and since he feared that if he altered them in any way they would be “mangled,” Descartes suppressed both.
But he never stopped working on physics and physiology. In particular, over the next few years, he wondered if the newfound conceptual unity between the heavens and the Earth would allow him to achieve a parallel mathematical unity. In other words, could he do to the terrestrial realm what astronomers had long done to the celestial realm: geometricize it? Geometry, after all, had originally been an attempt to render the terrestrial world in mathematical terms. Now, after a lapse of a couple of millennia, it was again, and in his 1637 Geometry, Descartes demonstrated how all matter, not only in heaven but on Earth, could be located according to three coordinates in space. In which case, as Descartes himself recognized and as succeeding generations came to appreciate, a crucial question presented itself: Could we approach the secrets of man’s inner universe with the same heretofore unthinkable curiosity that Galileo and his successors had regarded the outer? Could we render the motions of matter within the brain as predictable as any planet’s through the heavens? In short, could there be a Newton of neurology?
Even while Newton was alive and evidence had begun to accumulate that his laws extend to the outermost reaches of the universe, the question inevitably had arisen whether those same laws might extend to the innermost reaches as well. In 1725, Richard Mead, an English physician, had produced mathematical formulations of the effects of planetary gravity on the human body. Expanding on that idea later in the eighteenth century, the German physician Franz Anton Mesmer proposed a gravitational attraction between animals, or what he called animal magnetism, whose existence he then claimed to demonstrate through public displays of hypnotism. In the early nineteenth century, efforts at quantifying psychic phenomena found a champion in the German philosopher Johann Friedrich Herbart, who conceived of the workings of the mind as “forces” rather than ideas, who explicitly invoked Newton in advocating the use of mathematical formulas to describe the motions of these forces, and who once declared, “Regular order in the human mind is wholly similar to that in the starry sky.”
In retrospect, though, any such earlier efforts to reduce the workings of the inner universe to a series of cause-and-effect laws were doomed. These would-be Newtons couldn’t have known it at the time, but they didn’t yet have access to a Galilean equivalent of neuroanatomical data—the moons, planets, and stars of the inner universe—to provide their speculations with a solid empirical foundation.
Did Freud? It was tempting for him to think so. It would have been tempting for anyone in his position to think so—not only because it’s always tempting for an ambitious intellect to think that the generation into which it’s fortunate enough to be born is the one in possession of just enough information to settle a question that has thwarted the great thinkers since antiquity but because the state of neuroanatomical knowledge at the close of the nineteenth century was different from any other period in the history of science. In fact, in 1894—only five years after Ramón y Cajal’s discovery that fibers from central nerve cells contact, not connect, and only three years after Waldeyer developed the neuron theory—one of Freud’s former instructors and colleagues from his laboratory days, Sigmund Exner, published his own attempt at a comprehensive neuroanatomy, Entwurf zu einer physiologischen Erklärung der psychischen Erscheinungen (Draft Toward a Physiological Explanation of the Psychological Features).
Like most physiologists of his era, Freud knew firsthand what the achromatic microscope could accomplish. He’d used the still-new instrument extensively as a student in the 1870s, then proved his mastery of it the following decade as a reliable, respected diagnostician at the General Hospital of Vienna, where one of his examinations drew praise in a contemporary medical journal for its “very valuable contribution” to a field “heretofore lacking in detailed microscopic examination.” And like many physiologists of his era, Freud knew firsthand what staining a microscopic sample could accomplish. He’d twice developed his own significant improvements on existing staining methods, first in 1877 “for the purpose of preparing in a guaranteed and easy way the central and peripheral nervous system of the higher vertebrate (mice, rabbits, cattle),” and again in 1883 “for the study of nerve tracts in the brain and spinal cord.” And like a few physiologists of his era, Freud had even anticipated the neuron theory itself, during his lecture before the Vienna Psychiatric Society in the early 1880s, several years before Ramón y Cajal proved it. Unable to locate a fiber that he could trace from one central nerve cell to another, he’d wondered if cells might therefore not ultimately connect.
In the wake of his failure with the “Psychology for Neurologists,” however, Freud began to consider another way to frame the problem: not as mind in opposition to brain—or at least not only mind in opposition to brain. Instead he began to think in terms of mind in opposition to itself.
“The starting-point for this investigation,” Freud later wrote, outlining his reasoning at this juncture, “is provided by a fact without parallel, which defies all explanation or description—the fact of consciousness.” On the most basic level, the workings of the mind remained a mystery. Even a thought, the fundamental unit of mind, doesn’t remain in consciousness for any length of time. “A conception—or any other psychical element—which is now present to my consciousness may become absent the next moment, and may become present again, after an interval, unchanged.” Forget for the moment the gap within the brain—between one neuron and the next, that space across which some “quantity” of “energy” must pass, as he’d tried to express the transaction in his “Psychology.” And forget, too, the gap between brain and mind—between the physical communication among neurons and the resulting psychical impressions. With this description of one of the most mundane of human occurrences—something out of “our most daily personal experience”—Freud had identified a gap within the mind itself: “In the interval the idea was—we do not know what.”
“Unconscious,” he called it, adopting the common adjective of the time. In a sense, all he’d done was work his way back to the assumptions that he and his contemporaries had inherited. Mind was mind, brain was brain, and one day, maybe, the two would meet. Brain anyone with the proper training and equipment could tease the secrets out of, slicing tissue, staining samples, subjecting fibrils to microscopic scrutiny at recently unthinkable powers of magnification and degrees of resolution. Mind, however, nobody could fully capture using a mechanical model of the brain—not yet, anyway. Mind, as Freud could observe for himself
