by The Science of Leonardo: Inside the Mind of the Great Genius of the Renaissance
At the core of Hippocratic medicine was the conviction that illnesses are not caused by supernatural forces, but are natural phenomena that can be studied scientifically and influenced by therapeutic procedures and wise management of one’s life.26 Thus medicine should be practiced as a scientific discipline and should include the prevention of illness, as well as its diagnosis and treatment. This attitude has formed the basis of scientific medicine to the present day.
Health, according to the Hippocratic writings, requires a state of balance among environmental influences, the way in which we live, and the various components of human nature. One of the most important volumes in the Hippocratic Corpus, the book on Airs, Waters and Places, represents what we might now call a treatise on human ecology. It shows in great detail how the well-being of individuals is influenced by environmental factors—the quality of air, water, and food, the topography of the land, and general living habits. During the last two decades of the fifteenth century, this and several other volumes from the Hippocratic Corpus were available to scholars in Latin, most of them derived from Arabic translations.27
The culmination of anatomical knowledge in antiquity was reached in the second century A.D. with Galen (Claudius Galenus), a Greek physician who resided chiefly in Rome, where he had a large practice. His work in anatomy and physiology, based partly on dissections of animals, greatly increased the ancient knowledge of the arteries, brain, nerves, and spinal cord. Galen wrote over one hundred treatises in which he summarized and systematized the medical knowledge of his time in accordance with his own theories. By the end of the ninth century, all his works had been translated into Arabic, and Latin translations followed in due course. The authority of the Galenic teachings was unchallenged until Leonardo’s time, although they were not founded on detailed knowledge of human organs. His dogmatic doctrines actually impeded medical progress. Nor was Galen successful in correlating his medical theories with corresponding therapies.
The medical bible throughout the Middle Ages and the Renaissance was the Canon of Medicine, written by the physician and philosopher Avicenna (Ibn Sina) in the eleventh century. A vast encyclopedia that codified the complete Greek and Arabic medical knowledge, Avicenna’s Canon was more elaborate than Galen’s works and had the advantage of being a single monumental opus rather than a collection dispersed in many separate treatises.
Medical teaching at the great universities was based on the classical texts of Hippocrates, Galen, and Avicenna, and concentrated on interpreting the classics, without questioning them or comparing them with clinical experience. Practicing physicians, on the other hand, many of them without medical degrees, used their own eclectic combinations of therapies.28 The best of them simply relied on the Hippocratic notions of clean living and the ability of the body to heal itself.
As medical theory and practice increasingly diverged, human anatomy gradually became an independent field of study. Leonardo da Vinci, who became the greatest Renaissance anatomist, never practiced medicine. In fact, Leonardo had a very low opinion of doctors. “Strive to preserve your health,” he wrote on a sheet of anatomical drawings, “in which you will be the more successful the more you are wary of physicians.”29
One of the earliest texts on anatomy was the Anatomia by Mondino de’ Luzzi, a professor at Bologna in the fourteenth century. He was one of the few medieval teachers who actually performed anatomical dissections himself.30 His text, much influenced by the Arab interpreters of Galen, gave rudimentary instructions for dissections without, however, specifying the exact position and nature of individual organs. Yet, because of its succinctness and utility, Mondino’s Anatomia was a standard textbook in medical schools in the fourteenth and fifteenth centuries.
LEONARDO AND THE CLASSICS
During the years of his extensive self-education in Milan,31 Leonardo familiarized himself with the principal classical texts. He not only accumulated a considerable personal library, but also consulted classical manuscripts in the private libraries of wealthy aristocrats and monasteries whenever he had an opportunity, or borrowed them from other scholars. His Notebooks are full of reminders to himself to borrow or consult certain books. Since he had only the most rudimentary knowledge of Latin, he studied Italian translations whenever he could obtain them, or sought out scholars who could help him with the Latin texts.
We know from Leonardo’s own accounts that he knew Plato’s Timaeus well. He also owned several of Aristotle’s works, in particular the Physics. His knowledge of the mathematical writings of Plato, Pythagoras, Archimedes, and Euclid was derived mostly from Luca Pacioli’s famous Renaissance textbook, which was written in Italian. When Leonardo and Pacioli became friends, Pacioli helped Leonardo deepen his understanding of mathematics, particularly geometry, by guiding him through the complete Latin edition of Euclid’s Elements.32
Leonardo’s interest in astronomy was largely confined to studying optical effects in the visual perception of the heavenly bodies. But he was well aware of the Ptolemaic model of planetary motions. He owned several books on astronomy and cartography, including Ptolemy’s celebrated Cosmography and a work by the Arabian astronomer Albumazar (Abu-Mashar).33 With regard to natural history, Leonardo, like most Renaissance humanists, was well acquainted with the works of Aristotle, Pliny the Elder, and Dioscorides. He studied an Italian edition of Pliny’s encyclopedic Natural History, printed in Venice in 1476, and read Dioscorides’ popular Materia Medica. His own work in botany, however, went far beyond those classical texts.34
Many of Leonardo’s greatest scientific achievements were in the field of anatomy, and it was this subject that he studied most carefully in the classical texts. He owned an Italian edition of Mondino’s Anatomy and used it as an initial guide for dissections of the nervous system and other parts of the body. Through Mondino, he became acquainted with the theories of Galen and Avicenna, and subsequently studied an Italian edition of Avicenna’s classic Canon of Medicine. Eventually Leonardo probably read some of Galen’s work in Latin, with the help of the young anatomist Marcantonio della Torre, whom he met during his second period in Milan.35 Having thoroughly studied the three principal medical authorities of his time—Galen, Avicenna, and Mondino—Leonardo had a solid foundation in classical and medieval anatomy, on which he built his own extraordinary accomplishments.
Leonardo da Vinci shared with his fellow humanists their great confidence in the capabilities of the human individual, their passion for voyages of exploration, and their excitement about the rediscovery of the classical texts of antiquity. But he differed dramatically from most of them by refusing to blindly accept the teachings of the classical authorities. He studied them carefully, but then he tested them by subjecting them to rigorous comparisons with his own experiments and his direct observations of nature. In doing so, I would argue, Leonardo single-handedly developed a new approach to knowledge, known today as the scientific method.
SIX
Science Born of Experience
Today’s modern word “science” is derived from the Latin scientia, which means “knowledge,” a meaning that was retained throughout the Middle Ages and the Renaissance. The modern understanding of science as an organized body of knowledge, acquired through a particular method, evolved gradually during the eighteenth and nineteenth centuries. The characteristics of the scientific method were fully recognized only during the twentieth century and are still frequently misunderstood, especially by the general public.
THE SCIENTIFIC METHOD
The scientific method represents a particular way of gaining knowledge about natural phenomena. First, it involves the systematic observation of the phenomena being studied and the recording of these observations as evidence, or scientific data. In some sciences, such as physics, chemistry, and biology, systematic observation includes conducting controlled experiments; in others, such as astronomy or paleontology, this is not possible.
Next, scientists attempt to interconnect the data in a coherent way, free of
internal contradictions. The resulting representation is known as a scientific model. Whenever possible, we try to formulate our models in mathematical language, because of the precision and internal consistency inherent in mathematics. However, in many cases, especially in the social sciences, such attempts have been problematic, as they tend to confine the scientific models to such a narrow range that they lose much of their usefulness. Thus we have come to realize over the last few decades that neither mathematical formulations nor quantitative results are essential components of the scientific method.
Last, the theoretical model is tested by further observations and, if possible, additional experiments. If the model is found to be consistent with all the results of these tests, and especially if it is capable of predicting the results of new experiments, it eventually becomes accepted as a scientific theory. The process of subjecting scientific ideas and models to repeated tests is a collective enterprise of the community of scientists, and the acceptance of the model as a theory is done by tacit or explicit consensus in that community.
In practice, these steps, or stages, are not neatly separated and do not always occur in the same order. For example, a scientist may formulate a preliminary generalization, or hypothesis, based on intuition or initial empirical data. When subsequent observations contradict the hypothesis, the researcher may try to modify the hypothesis without giving it up completely. But if the empirical evidence continues to contradict the hypothesis or the scientific model, the scientist is forced to discard it in favor of a new hypothesis or model, which is then subjected to further tests. Even an accepted theory may eventually be overthrown when contradictory evidence comes to light. This method of basing all models and theories firmly on empirical evidence is the very essence of the scientific approach.
All scientific models and theories are limited and approximate. This realization has become crucial to the contemporary understanding of science.1 Twentieth-century science has shown repeatedly that all natural phenomena are ultimately interconnected, and that their essential properties, in fact, derive from their relationships to other things. Hence, in order to explain any one of them completely, we would have to understand all the others, which is obviously impossible. This insight has forced us to abandon the Cartesian belief in the certainty of scientific knowledge and to realize that science can never provide complete and definitive explanations. In science, to put it bluntly, we never deal with truth, in the sense of a precise correspondence between our descriptions and the described phenomena. We always deal with limited and approximate knowledge.
This may sound frustrating, but for many scientists the fact that we can formulate approximate models and theories to describe an endless web of interconnected phenomena, and that we are able to systematically improve our models or approximations over time, is a source of confidence and strength. As the great biochemist Louis Pasteur put it, “Science advances through tentative answers to a series of more and more subtle questions which reach deeper and deeper into the essence of natural phenomena.”2
LEONARDO’S EMPIRICAL APPROACH
Five hundred years before the scientific method was recognized and formally described by philosophers and scientists, Leonardo da Vinci single-handedly developed and practiced its essential characteristics—study of the available literature, systematic observations, experimentation, careful and repeated measurements, the formulation of theoretical models, and frequent attempts at mathematical generalizations.
The full extent of Leonardo’s method has come to light only recently with the accurate dating of his notes, which now makes it possible to follow the evolution of his ideas and techniques. For centuries, published selections from his Notebooks were arranged according to subject matter and often presented contradictory statements from different periods of Leonardo’s life. But during the last three decades the Notebooks have finally been dated properly.
The critical examination and dating of old manuscripts, known as paleography, has grown into a sophisticated science.3 In the case of the Notebooks, the dating involves not only evaluating actual dates, references to external events, and various cross-references in the text, but also a meticulous analysis of the evolution of Leonardo’s style of writing and drawing over his lifetime; his use of different types of paper (often with distinctive watermarks) and of different kinds of pens, ink, and other writing materials at different times; as well as comparing and piecing together a host of stains, tears, special folds, and all kinds of marks added by various collectors over the centuries.
As a result of this painstaking work, performed for several decades under the leadership of Carlo Pedretti, all of Leonardo’s manuscripts are now published in facsimile editions together with carefully transcribed and annotated versions of the original texts. Passages from different periods of Leonardo’s life—sometimes even on the same folio of a manuscript—have been dated accurately. These scholarly publications have made it possible to recognize the developments of Leonardo’s theoretical models, and the gradual perfection of his methods of observation and representation on the page, and thus to appreciate aspects of his scientific approach that could not be recognized before.4
One revolutionary change Leonardo brought to natural philosophy in the fifteenth century was his relentless reliance on direct observation of nature. While the Greek philosophers and scientists had shunned experimentation, and most of the Renaissance humanists uncritically repeated the pronouncements of the classical texts, Leonardo never tired of emphasizing the importance of sperienza, the direct experience of natural phenomena. From his earliest entries, when he began his scientific investigations, to his final days, he sprinkled his Notebooks with declarations about the critical importance of methodical observation and experimentation.
“All our knowledge has its origin in the senses,” he noted in his first Notebook, the Codex Trivulzianus.5 “Wisdom is the daughter of experience,” we read in the Codex Forster,6 and in his Treatise on Painting, Leonardo asserted: “To me it seems that those sciences are vain and full of errors that are not born of experience, mother of all certainty…. that is to say, which do not at their beginning, middle, or end pass through any of the five senses.”7 Such an approach to the study of nature was unheard-of in Leonardo’s day, and would fully emerge again only in the seventeenth century, the era of the Scientific Revolution.
Leonardo despised the established philosophers who merely quoted the classical texts in Latin and Greek. “They strut about puffed up and pompous,” he wrote scornfully, “decked out and adorned not with their own labors but with those of others.”8 He recognized that learning from skilled masters was important in the arts, but he also observed that such masters were rare. “The surer way,” he suggested, “is to go to the objects of nature, rather than those that are imitated with great deterioration, and so acquire sad habits; for he who can go to the well does not go to the water jar.”9
When he was over sixty and living in Rome, Leonardo, one day, was working on problems of mechanics, filling the pages of a small notebook with a series of elaborate diagrams of scales and pulleys. “I shall now define the nature of composite scales…,” he wrote at one point. And then—as if suddenly mindful of future readers who needed to be taught about science—he interrupted himself to add his now famous manifesto on his scientific method:
But first I shall do some experiments before I proceed farther, because my intention is to cite experience first and then with reasoning show why such experience is bound to operate in such a way. And this is the true rule by which those who speculate about the effects of nature must proceed.10
In the intellectual history of Europe, Galileo Galilei, who was born 112 years after Leonardo, is usually credited with being the first to develop this kind of rigorous empirical approach and is often hailed as the “father of modern science.” There can be no doubt that this honor would have been bestowed on Leonardo da Vinci had he published his scientific writings during his lifetime, or had his Notebooks been wide
ly studied soon after his death.
The empirical approach came naturally to Leonardo. He was gifted with exceptional powers of observation and a keen visual memory, complemented by his great drawing skills.11 Art historian Kenneth Clark suggests that Leonardo had an “inhumanly sharp eye with which…he followed the movements of birds or of a wave, understood the structure of a seed-pod or skull, noted down the most trivial gesture or most evasive glance.”12
What turned Leonardo from a painter with exceptional gifts of observation into a scientist was his recognition that his observations, in order to be scientific, needed to be carried out in an organized, methodical fashion. Scientific experiments are performed repeatedly and in varying circumstances so as to eliminate accidental factors and technical flaws as much as possible. The parameters of the experimental setting are varied in order to bring to light the essential unchanging features of the phenomena being investigated. This is exactly what Leonardo did. He never tired of carrying out his experiments and observations again and again, with fierce attention to the minutest details, and he would often vary his parameters systematically to test the consistency of his results. “We can only marvel at the master’s voracious appetite for details,” wrote art historian Erich Gombrich. “His range of activities and his insatiable thirst for knowledge seem never to have come in conflict with that awe-inspiring power of concentration that made him study one plant, one muscle, one sleeve or indeed one geometrical problem as if nothing else would ever concern him.”13
