Hektoen International

A Journal of Medical Humanities

Head and hand: Claude Bernard’s experimental medicine

James A. Marcum
Waco, Texas, United States


Photo of Claude Bernard
Claude Bernard. Source: National Library of Medicine, the hisotry of medicine public domain image files.

Claude Bernard’s Introduction à l’étude de la médecine expérimentale, originally published in 1865, occupies a critical position in the development of experimental medicine and science.1 In the introduction to the book, Bernard claims that “each kind of science presents different phenomena and complexities and difficulties of investigations peculiarly its own.”2 Although the various natural sciences investigate different phenomena using experimental methods unique to that science, according to Bernard, they do share a “common” or general experimental method.

“To be worthy of the name, an experimenter must be at once theorist and practitioner. While he must completely master the art of establishing experimental facts . . . he must also clearly understand the scientific principles which guide his reasoning through the varied experimental study of natural phenomena. We cannot separate these two things: head and hand. An able hand, without a head to direct it, is a blind tool; the head is powerless without its executive hand.”3

Bernard combines both rationalism and empiricism—with the metaphor of head and hand—into a common or general experimental method. His articulation of experimental method in terms of the head and hand metaphor is relevant for addressing the traditional debate between rationalists and empiricists.

The debate between rationalists and empiricists is centuries if not millennia old, especially within medicine.4 During the nineteenth century, the debate crystallized into the “standard narrative” of “the rationalism of Descartes, Spinoza, and Leibniz” vs. “the empiricism of Locke, Berkeley, and Hume.”5 As for rationalism, it was a popular topic within the medical literature of the nineteenth century, with various physicians providing definitions of it.6 For example, Alexander Henry, in a paper read before the Medical Society of London on March 25, 1854, defines rationalism as a “mode of inquiry in which observations are made for the purpose of being reasoned on, and where experiments are performed as the means to an end, and as a test of the truth of what has been conceived beforehand.”7 But the various definitions did share a common theme: rationalism is the belief that reason—in contrast to the senses or experience—is the source of knowledge and the senses or experience simply play an ancillary role at best in knowing. Moreover, rationalists insist that innate knowledge and categories like space, time, and causation, which are prior to experience, are responsible for knowing. They emphasize reason and rational faculties as the source of knowing and understanding, for reason provides the cognitive and epistemic resources and framework not simply for understanding sensory observations but also for identifying which sensory observations are important to understand in the first place.

On the other hand, empiricism is the belief that the source of knowledge—in contrast to reason—is experience, especially through the senses. Just as rationalism was a popular topic within the medical literature of the nineteenth century, so was empiricism, if not more so. Again, to quote Henry, empiricism is “a system based on the mere observation of facts without deductions, and on experiments made at hazard, without any precise or preconceived object.”8 A good example of empiricism within the French medical community was François Magendie, who employed Bernard as an assistant. According to José Recio,

“Magendie’s empiricism, an enemy of hypotheses and theories, opposed to reasoning becoming a part of observation, could be defined by a sentence which Magendie often repeated: ‘When I experiment, I have only my eyes and my ears, I have absolutely no brain.’”9

Empiricism, especially within medicine, involves remedies based on experience without recourse to understanding the cause of the illness. Empiricists, particularly in contrast to rationalists, emphasize sensory observation and experience as the source of factual knowledge, and they have little, if any, use for reason or the rational faculties in terms of the source for knowledge since knowledge is not possible unless first in the senses.

Bernard’s notion of experimental method as articulated with the metaphor of head and hand has important implications for addressing the debate between rationalists and empiricists. Rationalism for Bernard is closely tethered to “philosophic systems,” which he cautions experimenters from embracing. “When a man of science takes a philosophic system as his base in pursuing a scientific investigation,” warns Bernard, “he goes astray in regions that are too far from reality, or else the system gives his mind a sort of false confidence and an inflexibility out of harmony with the freedom and suppleness that experimenters should always maintain in their researches.”10 Bernard then proceeds to inform the reader that “philosophy, lacking the support or the counterpoise of science would rise out of sight and be lost in the clouds.”11 In other words, philosophy qua rationalism would posit conjectural or hypothetical entities unless yoked to science qua empiricism. The epistemic fear for Bernard is that left to itself rationalism might conceive or postulate anything. Observation or experience, then, should provide an empirical framework to constrain or prevent reason from positing artefact from speculative or unrestrained cognitive activity. Reason needs to point to observations such that the latter directs the former. Or, to quote Bernard, “if we made an hypothesis which experiment could not verify, in that very act we should leave the experimental method to fall into the errors of the scholastics and makers of systems.”12

Besides empiricism directing rationalism, rationalism can guide empiricism. According to Bernard,

“Empiricism, which means experience at bottom (ἐμπειρία, experience), is only unconscious or non-rational experience, acquired by ever-day observations of facts, in which the experimental method itself originates . . . empiricism in its true sense is merely the first step in experimental medicine.”13

For Bernard, although science is not simply equivalent to empiricism—“Empiricism may serve to accumulate facts, but it will never build science.”14 Still science, especially experimental science or medicine, is at its roots empirical or experiential in nature. With this in mind, Bernard then claims that “science without guidance and high aspiration [from philosophy], would sail at random.”15 In other words, science qua empiricism would flounder in designing and conducting experiments and interpreting experimental results unless guided by philosophy qua rationalism. The epistemic fear for Bernard is that empiricists might not know what observations are important or even how to interpret them meaningfully. Observations must be potentially reasonable or intelligible, otherwise they run the risk of being meaningless. To make observations with no reasonable means for interpreting them is futile, simply because observations are not facts. A fact is the cognitive product of intelligibility when interpreting observations. If reasonable insights or inferences cannot be expected from analyzing the patterns found in observations, then what is the point of collecting them? “Men who gather observations,” according to Bernard, “are useful only because their observations are afterward introduced into experimental reasoning; in other words, endless accumulation of observations leads nowhere.”16

In conclusion, for Bernard, both rationalism and empiricism are required for the successful practice of experimental science and medicine; and to a large extent they complement or supplement one another in that the rational head and the empirical hand must cooperate with one another. They cannot function independently but rather must work together in a harmonizing fashion. Otherwise, as Bernard warned early in his book, without the head the hand is “a blind tool” while the head without a hand is “powerless.”17 For Bernard, an experimenter regardless of the natural science is embodied, i.e., with the head of rationalism and the hand of empiricism.


End Notes

  1. John E. Lesch, Science and Medicine in France: The Emergence of Experimental Physiology, 1790-1855 (Cambridge, MA: Harvard University Press, 1984). J.M.D. Olmsted and E. Harris Olmsted, Claude Bernard and the Experimental Method in Medicine (New York: Schuman, 1952).
  2. Claude Bernard, An Introduction to the Study of Experimental Medicine, trans. Henry Copley Greene, (New York: Schuman, 1949).
  3. Ibid. 3.
  4. Harris L. Coulter, “Empiricism vs. Rationalism in Medicine,” Journal of Orthomolecular Medicine vol. 9 (1994): 159-159. Benjamin Murphy, “Rationalism and Empiricism: Will the Debate Ever End?” Think vol. 9 (2010): 35-46. Warren Newton, “Rationalism and Empiricism in Modern Medicine,” Law and Contemporary Problems vol. 64 (2001): 299-316.
  5. Alberto Vanzo, “Empiricism and Rationalism in Nineteenth-Century Histories of Philosophy,” Journal of the History of Ideas vol. 77 (2006): 253.
  6. William Odling, “Introductory Address Delivered at St. Bartholomew’s Hospital Medical School. Session 1867-68,” Lancet vol. 90 (1867): 415-421. W. H. Walshe, “Lectures on Clinical Medicine, Lecture I,” Lancet vol. 53 (1849): 1-5.
  7. Alexander Henry, “The Relative Merits of Empiricism and Rationalism in the Present State of Medical Science,” Association Medical Journal vol. 2 (1854): 327.
  8. Ibid. 327.
  9. José Luis González Recio, “Who Killed Histological Positivism? An Approach to Claude Bernard’s Epistemology,” Ludus Vitalis vol. 12 (2017): 68.
  10. Bernard, Introduction, 221.
  11. Ibid. 224.
  12. Ibid. 33.
  13. Ibid. 204.
  14. Francisco Grande, “Introduction to the Symposium,” in Claude Bernard and Experimental Medicine, eds. Francisco Grande and Maurice B. Visscher, (Cambridge, MA: Schenkman, 1967), 8.
  15. Bernard, Introduction, 224.
  16. Ibid. 25.
  17. Ibid. 3.



JAMES A. MARCUM, PhD, is professor of philosophy at Baylor University. He earned doctorates in physiology from the University of Cincinnati Medical College and in philosophy from Boston College. He was a faculty member at Harvard Medical School as a molecular biologist for over a decade before joining Baylor’s philosophy department. His research interests include the philosophy and history of medicine and science. He has published eight books and examples of his articles appear in American Journal of Physiology, Journal of Biological Chemistry, Journal of Clinical Investigations, Journal of the History of Medicine, Synthese, and Theoretical Medicine and Bioethics.


Summer 2021  |  Sections  |  Science

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