To Reductionism and Beyond

My patient has a cough, fever and crackles at the left lung base.  The chest radiograph shows an infiltrate.  “You have pneumonia,” I tell him.  “The Thoracic Society guidelines recommend a macrolide antibiotic to cover for Streptococcus pneumoniae and atypicals. Here is your prescription…”

“But doc, how do you know I will get better?  I don’t feel well.  My grandmother died of pneumonia and she was given the exact same prescription.”

Such questions often draw empathetic platitudes, or perhaps a discussion of clinical trials if time allows.  But the real answers strike at the core of what we do as physicians, and reflect on the troubled relationship of medicine to society.  We are not taught to provide comprehensive answers to questions of why we do what we do. Yet this ignorance undermines the trust that “is essential to patients in their willingness to submit to treatment.  They must be willing for us to be able.” (Jacobs 2005)

We practice medicine in certain ways because we have seen them work, and because we have read about them working — in “the literature” — but do we know why we trust our experience and our studies?  The instinctive reaction to cite studies does not really explain why your patient should trust his or her life to those studies.  Studies simply aggregate many cases of a similar disease in sophisticated “evidence-based” ways.  “What does that study have to do with me?” asks the astute patient.  The question is as old as civilization itself, and one that Aristotle (384–322 BCE) pondered in his discussions of “primitives”, or individual cases, in the context of making a general conclusion.

Now some think that because one must understand the primitives there is no understanding at all… for it is impossible to go through infinitely many things.

–Aristotle, Posterior Analytics

Trying to review “infinitely many things” raises the fundamental philosophical question of induction, or drawing conclusions about the general case from examining numerous particular instances.  We make a leap, from the individual to the general.  In Aristotle’s model, without a conception of scientific investigation, this leap was derived from tradition, and required the use of “phronesis” or practical wisdom.  Much of current medical practice continues to rely on practical wisdom in a way that Aristotle would recognize.  After all, most of medical practice is still not “evidence-based.”

However, we also believe that pneumonia will improve with azithromycin because we believe that induction works.  After studying many cases of pneumonia, we can make a prediction about a future case of pneumonia.  The statement sounds fairly bland when put this simply, but actually reflects a fundamental leap in philosophical reasoning that we often take for granted as medical providers, and that our patients may not deeply understand.

David Hume (1711-1776) reacted to the entire tenuous edifice of pre-scientific thought by introducing a deep skepticism towards causation and inductive knowledge.  He realized that the attempts to explain scientific facts by appeals to phenomena such as “the humors” — Hippocrates–, or by observing that the stars turn and thereby “…establish that the earth occupies the middle place in the universe” — Ptolemy — were fruitless and prone to error.  There was no logical connection between the conclusions and the supposed facts given to reach those conclusions.  For Hume, humans are left only with our experience of an event that we use as a “reason” to justify a conclusion about what caused it.

“Causes and effects are discoverable, not by reason but by experience…” Hume realized.   And based on our experience, we expect the “future to be conformable to the past.” (McGrew 2009)  However, without some theory, or rational explanation, behind our investigations, we have no basis beyond experience to predict the future.  And experience can be a fickle master as he demonstrates in his famous quote about fresh eggs:

Nothing so alike as eggs; yet no one, on account of this appearing similarity expects the same taste and relish in all of them.

Patients frequently commit the error of equating their experience with causation.  With a little reflection, we see that we all do so.  The philosophical school of logical positivism developed to show how observational evidence could provide genuine support for a scientific theory.  Hans Reichenbach (1891-1953) introduced the idea of the wager, or the odds of an induction being true.  We justify our use of induction by arguing that if there is any reliable method of predicting the future on the basis of the past, induction is it.

Hume demanded too much when he wanted for a justification of the inductive inference a proof that his conclusion is true.  What his objections demonstrate is only that such a proof cannot be given.  We do not perform, however, an inductive inference with the pretension of obtaining a true statement.  What we obtain is a wager; and it is the best wager we can lay because it corresponds to a procedure.

The positivists abandoned the idea of objective truth behind scientific knowledge in favor of simply reproducible explanation.  And certainly much of my day to day medical advice and treatment reflects this loss: “I don’t know why this works, or what is going on in the body, but studies show that it does.”  The logical positivists represent a form of empirical thought that posits that the only source of knowledge is experience.  Empiricist explanations are often not very satisfying, especially for patients and their families, but they do get the job done in the form of Evidence Based Medicine.

Modern medicine has made its most spectacular advances applying empirical observation to ever smaller biological processes by isolating single variables and testing them, a process known as Reductionism.  But biomolecules are not humans, and complex questions of how attitude or prayer might affect cancer outcomes is left to the “art of medicine.”  Contemporary philosophers such as Thomas Nagel in Mind and Cosmos question whether further scientific advances will require studying whole systems rather than just parts.  Nagel does not see reductionism as satisfactory for explaining the operation of the mind; neuroscience can tell us how molecules cause nerves to fire, but not how consciousness is created.  

The existence of consciousness seems to imply that the physical description of the universe, in spite of its richness and explanatory power, is only part of the truth…

For modern scientific medicine, the physical description of the body is what we rely on implicitly, and everything else is compartmentalized as “bedside manner.”  Nagel’s critique goes on to show that the existence of mind challenges Darwinian “blind” evolution.  Only if there exists some teleology, or intrinsic destination, for evolution can one explain the emergence of consciousness.

To explain consciousness, a physical evolutionary history would have to show why it was likely that organisms of the kind that have consciousness would arise… There [might be] natural teleological laws governing the development of organization over time, in addition to laws of the familiar kind governing the behavior of the elements.

Patients facing serious illness or death often find comfort in the idea that their lives have meaning — even if it is not always religious meaning.  The holistic consciousness that Nagel describes is currently scientifically inaccessible to us.  Will humanity’s yearning to be seen as more than a collection of parts always remain at the level of clinical art, or could it emerge in a scientific manner and become amenable to reproducible study?  Will the line between the “art” of medicine and the “science” always remain drawn where it is now?

As our culture becomes increasingly diverse and skeptical of claims about “truth”, a working familiarity with the philosophy of science becomes helpful to medical providers.  Scientific medicine is more openly debated in the marketplace of ideas now than ever.  Every one of my patients wonders whether he or she should be seeing me rather than the curandera, the naturopath, or Google.  And if they do see me, they wonder if I know what I am doing, and why they should trust me with their lives.  And these are good questions, ones that we should embrace because they deserve answers rather than trite statements like, “Because this is how I was trained.”



Jacobs, A. K.. “Rebuilding an Enduring Trust in Medicine: A Global Mandate: Presidential Address American Heart Association Scientific Sessions 2004.” Circulation 111.25 (2005): 3494-3498. Print.

Aristotle. Posterior Analytics.  In McGrew, Timothy J. ed. Philosophy of science: an historical anthology. Chichester: Wiley-Blackwell, 2009. Print. Page 46.

McGrew, Timothy J. ed. Philosophy of science: an historical anthology. Chichester: Wiley-Blackwell, 2009. Print. Page 220-224.

Godfrey-Smith, Peter. Theory and reality: an introduction to the philosophy of science. Chicago: University of Chicago Press, 2003. Print. Page 173.

Nagel, Thomas. Mind and cosmos: why the materialist neo-Darwinian conception of nature is almost certainly false. New York: Oxford University Press, 2012. Print.

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