Medical Maxims: Two Views of Science


Both authors are Research Fellows in the Division of Primary Care and Family Medicine, Harvard Medical School, Boston. MA.

[a] Division of Primary Care and Family Medicine, Harvard Medical School, Boston, Massachusetts; [b] Department of Psychology and Social Relations, Harvard University, Cambridge, Massachusetts

Received March 5. 1979

Address reprint requests to: Dr. Harold Bursztajn. Division of Primary Care and Family Medicine. Harvard Medical School. Boston. MA 02115

Clinicians are beings with finite minds and thus need to use simplified models of the world in making decisions [1]. However, these models need not be oversimplified. as are the models encouraged by the prevalent view of science, the Mechanistic Paradigm, which are articulated as rigid maxims. A more current view of science, the Probabilistic Paradigm, encourages more complex models, which can be articulated as the more flexible maxims used with insight by the wise clinician.

Some maxims help in clinical practice, and others too often become rigid rules. No doubt much depends on skill, which the practitioner gains only with experience. But the view of science that the medical student learns plays no small role in making the acquisition of sufficient experience take longer and be perhaps more painful than is needed.

The medical student learns that science is concerned with causal laws that determine events with certainty, laws which themselves are established with certainty by this or that crucial laboratory experiment. In this view the intuitions of the investigator are the sort of subjectivity that had best be separated from the "objective" data that experiments can provide. This view or paradigm [2] takes its inspiration from Newton's view [3] of what physics, the "queen" of sciences, ought to be. It became so successful in the nineteenth century, when Newtonian mechanics and the industrial age marched forward hand in hand, that it might well be called the "Mechanistic Paradigm."

Emphasis upon this Mechanistic Paradigm does not stop in the preclinical years. The founders of modern medicine took the elimination of uncertainty, "mere probability," as an ideal to be practiced everywhere from the laboratory bench to the patient's bedside. Medical practice was to aspire to what Isaac Newton would have the physicist do in the laboratory. Thus Claude Bernard wrote:

I acknowledge my inability to understand why results taken from statistics are called laws; for in my opinion scientific law can only be based on certainty, on absolute determination, not on probability. What a physician needs to know is whether his patient will recover and only the search for scientific determinism can lead to his knowledge [4].

The rules of thumb that the clinician first learns in his pursuit of medical wisdom appear to give the straightforward and certain guidance that Newton would have required of his physicist and Bernard of his physician. Thus, there are maxims such as "Unexplained amenorrhea calls for X-ray study of the skull for pituitary tumor" [5]. Desiring to do the right thing, and anxious not to do the wrong thing, the intern or resident all too naturally takes this sort of maxim as a rigid rule whose use discharges his responsibility for decision making under these uncertain conditions.

When the maxim has the tone of scientific authority, it is easy enough to use it to justify one's decisions, and to consider one's practice to be on a par with the use of the deterministic causal laws that scientists discover. By following this maxim, one can be sure to put one's finger on the cause of amenorrhea, through performing the crucial experiment—the X-ray. Nowhere is there room for one's intuitions regarding this patient. These are considered "subjective," and thus not worthy of the sort of attention one would pay to the "objective" data, the X-ray. No doubt maxims in this Mechanistic Paradigm style help the busy house officer to be decisive and give him the feeling that he has gotten to the bottom of things. But relying strictly on such maxims produces problems.

Since the above maxim was written, it has been dated by developments in technology, such as computerized tomography. However, the uncertainty surrounding the use of such maxims is not solely due to the pace at which better diagnostic and therapeutic techniques are developed. The wise clinician knows well that not only technology but patients, diseases, and their causes change in the course of time. He keeps an eye out for causes which come and go as the disease progresses, causes that can only be expressed in probabilistic terms. Thus, he avoids favoring one or even several causes that are constantly before him because the diagnosis has been made. In so doing, his treatment of the patient and the patient's disease is not guided solely by the causes that were well articulated and influential when the original decision was taken. Stated this way, it is easier to understand how the wise clinician avoids an error that the house officer is prone to make.

For example, it was the experience of one of the authors that a child subjected to an extensive series of diagnostic procedures for failure to thrive at home failed to thrive in the hospital. The fact that he deteriorated in the hospital spurred ever more forceful pursuit of a policy of invasive diagnostic testing. Faced with a downhill clinical course, the house officers only redoubled their efforts to get to the bottom of things and find a certain cause for the illness.

In this case, it is not enough to say that the house officers should have tried harder. Nor is it enough to suggest that a rule of thumb such as, "In a child under the age of two presenting as a failure to thrive, in your investigations try to avoid increasing the disease." be added to the set of maxims. Such a maxim has already been taught to the beginning clinician: "Primum non nocere." One cannot learn a maxim for every situation; even had a maxim been learned for this situation, there is no guarantee that it would have been used wisely.

The road open to the wise clinician, yet closed to the house officers because of their adherence to the Mechanistic Paradigm of science, was to consider the possibility that the set of causes of the child's failure to thrive at the outset had changed in the course of hospitalization to include the stress of repeated invasive diagnostic procedures. But the maxims which guided the house officers in their search for the crucial piece of data, which the next diagnostic procedure (the "crucial experiment") always seemed to promise, had no provision for reconsideration. The house officers' discomfort with the road they had chosen, and their intuitions that perhaps it was time to stop testing for the cause of the failure to thrive, and to concentrate on nutrition and other supportive care, were considered "subjective feelings" and accordingly dismissed.

The wise clinician decides, but is aware that the causes he has acted on may change in the course of time. He is mindful of how time, the twisting course of the patient's disease, and changes in the patient's evaluation of his situation (as, for example, the feelings of the terminal cancer patient about being alive change as pain increases) affect what is being treated and what it is important to treat. Therefore, for the wise clinician neither data nor maxims are a substitute for judgment. Neither can be treated as if it were obtained from some crucial experiment which allows one to close one's mind to alternative courses of action. Not only do data (such as X-rays) and maxims (such as that cited above) require interpretation, but also their relevance to the alternative paths being considered may be uncertain. In fact, choice of the path to pursue initially in a case begins with the clinician's intuition as to what is probable and what is valuable in this case.

The clinician is not only an observer but a participant [6] and just as what he says may affect the patient's values over time, so diagnostic procedures may affect what is being treated. The very act of putting one's finger on "the cause" may contribute to the coming and going of other causes.

The wise clinician learns all this in the course of his experience, and there exist maxims which reflect this learning better than those stated earlier. For example, "When symptoms of viral hepatitis with jaundice recur after a year, additional causes should be suspected" [7]. This maxim recognizes that diseases can change, and, whether or not one had one's finger on the cause to begin with, causes may come and go in a manner that cannot be predicted with certainty at the outset. Maxims that begin with probability, rather than with certainty, are more faithful to the wisdom of the experienced clinician.

Where do such insights, when embodied in the skillful use of a set of flexible maxims, fit in the world of medical practice? Traditionally, they have been relegated to the art of medicine, for the Mechanistic Paradigm, with its notions of laws with certain causes, crucial experiments, and objectivity, encourages neither flexible maxims nor their insightful use. However, there is another view of science that is compatible with such insights. Although this view is influential in such diverse areas as ecology, evolution, and economics [8], it finds its clearest statement in the physics of the twentieth century. The general view of science held by such quantum physicists as Heisenberg [9] stands in stark contrast to the Mechanistic Paradigm of Newton.

This other view of science, the Probabilistic Paradigm, recognizes that it is in the nature of things that causal laws speak in terms of the probabilities rather than the necessities of events. In the realm of events that are of concern to medicine, such as diseases, there is thus an element of irreducible statistical variability in the connections from causes to diseases. The result is that the course of the disease cannot be predicted with complete confidence.

The Probabilistic Paradigm provides caveats not only about the limited extent to which the course of a disease is predictable, but also about the limited reliability of diagnostic tests. Making a diagnosis depends on some causal relation between the cause of the disease and the sign that the doctor recognizes, whether it be a symptom or a test result. When we understand causal relations to be probabilistic, then there is scientific justification for the intuition that diagnostic evidence is fallible. There is thus not only room but also need for human judgment in deciding whether to accept the standard implication of even the best of tests.

There is yet a further principle that the Probabilistic Paradigm of science encourages us to be aware of. Where the Mechanistic Paradigm's Newtonian view of science encourages us to take, as the norm, eradication of the influence of the experimenter on the outcome of the experiment, the Uncertainty Principle of Heisenberg encourages us to recognize that such influences are inevitable, and to be attentive to their effects. In medical practice this principle means keeping in mind the role of the observer, the experimenter, or the diagnostic test, as a cause in the disease process. The way we use our maxims, and the maxims themselves, must reflect our knowledge that diagnostic procedures can have effects on the causes of the diseases, or on the patient's experience of the disease.

The wise clinician's practice is consistent with the scientific principles of the Probabilistic Paradigm. Specifically, his or her practice exemplifies an awareness of the following principles: that a probabilistic reality contains within it a necessary kernel of uncertainty as to the causes of events; that given this uncertainty, even the best of tests can only point to causes as likely, rather than necessary; moreover, that the very act of diagnosing a disease may alter the disease itself, for the scientist with his instruments is not only an observer but also a participant, and how he participates cannot be predicted with certainty.

There is no absolute substitute for the experience which guides the wise clinician in skillfully using flexible maxims. However, the Probabilistic Paradigm provides some guideposts which, if followed, can shorten the road to clinical wisdom. The learning clinician can be best guided by the experienced clinician if the latter can articulate his insights in maxims which are flexible in form so that they can remind the user of the principles of the Probabilistic Paradigm. A clinician who keeps such principles in mind is more likely to use the maxims skillfully.


Thanks are due to Maya Bar Hillel, A. Stone Freedberg, Leston Havens, R. Duncan Luce, Robert S. Lawrence, and John Stoeckle for valuable comments on previous drafts.


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