John Locke

Patrick Guinan, M.D.

It is not widely known that the great English  philosopher John Locke was also a physician. He indeed spent much of his life in research and medicine, and according to Sir William Osler medicine was his “first love”.

John Locke (1632-1704) was born in the village of Wrington in Somersetshire. He  entered the humanities program at Oxford in 1652, obtaining a bachelor of arts degree in 1656 and master of arts degree in 1658; and he remained at Oxford as a tutor and lecturer in philosophy until 1664. Undecided at first whether to pursue a career in theology or in medicine, his interest in the natural sciences led him to choose the latter.

From 1666 until 1675, when he received his bachelor of medicine degree, he studied and practiced medicine, working at first with Robert Hooke, Richard Lower and Robert Boyle, all of whom were corpuscular physiologists.  Boyle especially had modified the classic Greek atomic theory into his own corpuscular philosophy, considering the whole fabric of the universe to consist of particles of corpuscles which joined together to form more complex groups, the only difference being the size, shape, configuration and motion.  During this time Locke also practiced medicine. He became personal physician of Lord Ashley Cooper, First Earl of  Shaftesbury and later Lord High Chancellor of England.  Among his closest associates he numbered John Mapletoft and Thomas Syndenham, both eminent English physicians, the latter acknowledged to be the father of English Medicine and sometimes called the English Hippocrates.

Locke spent the years 1675 to 1679 in France, primarily for health reasons. There he devoted most of his time to medicine and science, visiting the medical school at Montpellier, and making rounds at Charité Hospital in Paris. Returning to England in 1679, he became more and more occupied with political matters and was closely associated the Earl of Shaftsbury, his patron.  After Shaftsbury’s political downfall in 1683 he went into exile in Holland and  did not return until 1690 after the powers of parliament, for which Locke was an apologist, were restored.

Title page for first edition

Locke considered himself first and foremost a physician. In his Latin notes he refered to himself as medicus and to his colleagues as “alii medici”.  Any depreciation of the influence of medicine in his life was dispelled in 1875 when Fox Bourne published his definitive biography acknowledging medicine as a prime influence on his life. He pursued his medical education with scientific experiments in physiology and pharmacology, but also studiously followed and observed Sydenham as he made bedside rounds.  While traveling in foreign lands it was his custom to carry notebooks filled with records of his continuous and almost compulsive observations of the ill.  As far as is known, he was as understanding and sympathetic as he was observant and deductive.  Although his practice was limited mostly to the well to do, particularly in his later years, all of his patients were treated with a sympathy and concern uncommon in physicians of his era. Locke was more the clinician than the innovator or discoverer of diseases. But his description of various illnesses, such as the treatment of advanced syphilis with mercury, are models of medical writing. One disease, onychogryphosis, was first described by him and still bears his epomyn.  Locke was probably the first to describe the lateral lithotomy position for stone removal to English physicians, and he also wrote a classic description of tuberculous nephritis with peritoneal involvement.

His clinicopathologic observations show insights unusual for the seventeenth century and emphasize the importance of controlled observation.  This Locke learned during the period when Sydenham was his mentor.  Sydenham was not so much a scientist as a clinician and observer.  He disparaged physicians who relied on experiments to determine the etiology and treatment of disease rather than on beside observations.  Sydenham’s profound influence on Locke can be noted in the subtle change that took place in his treatment of patients as recorded in his notes.  Before his association with Sydenham, Locke practiced medicine as it was practiced by most other physicians, i.e. with recourse to medieval purges, herbs and nostrums that had little to do with the clinical condition of the patients.  After his association with Sydenham, Locke put more stock in his clinical acumen and developed a method of observation that he would also adopt in his philosophical studies.

Locke, the father of empiricism and associationism, wrote his major philosophic work, An Essay Concerning Human Understanding, in 1690.  He also wrote Two Treatises on Government and other important works which dealt with politics, education, and toleration which were not purely philosophical. The Essay is famous for two major reasons: its empiricism and its associationism.  The empiricism arose from Locke’s desire to account for the origin of ideas which he did not feel had been adequately accounted for by Descartes.  His “plan historical” method was principally introspective and led with Berkeley and Hume to skepticism.  His associationism has profoundly influenced modern psychology and has had great effect on Germanic psychology, systematic British psychology, and is the philosophical parent of experimental psychology. The Essay can be summarized into three main points,  all reflecting the influence of Locke’s medicine and science on his philosophy.  The first point is a cogent refutation of Descartes's theory of innate ideas.  Indeed, this is the reason for the entire Essay.  Quite simply, Locke wanted to account for the origin of our ideas.  This refutation would seem to be at odds with his original apparently favorable opinion of Descartes's work. This refutation of Descartes's theory is based on Locke’s second premise in the Essay, his method of observation of his “empiric method”.  He examines he own thoughts and ideas and finds that they all invariably arrive from sense experiences.  Thus, Locke’s contribution of method of epistemology is an outgrowth, in great part, of his association with Sydenham and the latter’s great emphasis on careful observation and thoughtful analysis of observed facts.

The third point Locke makes in the Essay is his theory of perception of ideas.  He postulates a passive observer and an object which gives off primary and secondary qualities which strike the senses of the observer and result in an idea.  This is similar to Boyle’s theory and is based in large part on the corpuscular theory which Locke acquired when he was a scientist and experimenter.  The inference that Locke’s thoughts and actions during his thirty productive adult years in medicine and science had a determining influence on his philosophy as expounded in the Essay is difficult to dispute.


PATRICK D. GUINAN, MD, MPH is a 1962 graduate of Marquette University Medical School. The author went on to obtain a graduate degree in Public Health from Columbia University in 1965. He is presently a Clinical Associate Professor in the Department of Urology in the College of Medicine at the University of Illinois at Chicago and serves as Chairman of the Board of the Hektoen Institute of Medicine.