Physic anno 1700

Speaking of the history of medicine and physicians, it is well-known that Gerard van Swieten was not only heavily influenced by the learnings of Hermann Boerhaave, but a champion of Boerhaave's work. In The Cambridge History of Science Volume 3: Early Modern Science (2006), Harold J. Cook uses Boerhaave as an example when summing up the state of physic at the beginning of the 18th century:

By the end of the seventeenth century, what had been for Avicenna a less than precise bodily "matter" expressing itself through flows of urine, feces, blood and phlegm had become materialized with precision. The fine structures of the body had been distinguished and their movements, growth, and changes were being charted. At the same time, the causal analyses that Avicenna had used had been fundamentally challenged. In the process, much had changed: Humors had disappeared, whereas bodily fluids, even lymph, had grabbed attention; it no longer mattered whether someone's temperament was sanguine or choleric, for her physiology was the same as her neighbor's. Not only had the basic principles of physic been undermined, opening new questions to study, but certainty had come to rest on knowledge of material detail. What might truly be called a research tradition had grown up in the medical ranks. Moreover, the hope that a new understanding of nature rooted in details might lead to the betterment of the human condition had clearly come to take pride of place in medicine.

The famous Institutiones Medicae (Medical Institutions, orig. ed. 1706) of Hermann Boerhaave (1668-1738) illustrates nicely how certainty now lay in material things rather than causal first principles. At Leiden, Boerhaave, taught a new generation of clinically and chemically oriented medical professors and physicians from all over Europe and Britain. He held that the truths of physic could be discovered only by observation supplemented with reason. This meant that all true physical knowledge was built on sense experience. Physic therefore could account only for those things "which are purely material in the human Body, with mechanical and physical Experiments." First causes "are neither possible, useful, or necessary to be investigated by a Physician." Looking back to his hero Hippocrates, Boerhaave explained that "the art of Physic was anciently established by a faithful Collection of Facts observed, whose Effects were afterwards explained, and their Causes assigned by the Assistance of Reason; the first carried Conviction along with it, and is indisputable; nothing being more certain than Demonstration from Experience, but the latter is more dubious and uncertain."

Boerhaave's contemporary, Baglivi, agreed entirely: Certainty in the knowledge of physic remained the end, "For the Art is made up of such things as are fully Survey'd, and plainly Understood, and of such perceptions as are not under the control of Opinion. It gives certain Reasons which are plac'd in due Order, and chalks out certain Paths, to keep its Sons from going astray. Now what is more uncertain than the Hypotheses?" As long as "Observation is the Thread to which Reason must point," all will be well. But "'tis manifest, that not only the Original of Medicine, but whatever solid Knowledge 'tis entituled to, is chiefly deriv'd from Experience." That certainty now resided in observation and experience of things was also clearly expresed by Boerhaave's and Baglivi's English contemporary Hans Sloane (1660-1753), who would later become President of both the Royal Society of London and the London College of Physicians. Sloane, too, wrote about how knowledge was no longer established on first principles but on physical observation:

"Knowledge based on Observations of Matters of Fact, is more certain than most Others, and in my slender Opinion, less subject to Mistakes than Reasonings, Hypotheses, and Deductions are ... These are things we are sure of, so far as our Senses are not fallible; and which, in probability, have been ever since the Creation, and will remain to the End of the World, in the same Condition we now find them." (p. 432-3)