The patient the trial cannot see: Clinical reasoning and mechanism in the age of precision medicine

Clinical reasoning at the bedside has historically been grounded in pathophysiological mechanism characterized by the causal understanding of what is happening in this particular patient's body. Over the past three decades, two developments have displaced that tradition: the institutionalization of evidence-based medicine, which elevated population-level statistical evidence above individual clinical reasoning, and the rise of molecular biology, which relocated scientific prestige from organ-level integrative physiology to the receptor and the gene. Together, they have produced a clinical culture in which mechanistic reasoning at the level of the individual patient lacks both institutional support and epistemological standing. We argue that this displacement has been costly, that it was never adequately diagnosed, and that recovering mechanistic reasoning while preserving the genuine contributions of both evidence-based medicine and molecular biology is now an urgent task for clinical medicine and medical education alike. Individualized patient care, the explicit goal of contemporary medicine, cannot be achieved within a purely probabilistic framework. Our argument is not against evidence-based medicine; its contributions to clinical practice are genuine and irreversible. It is an argument for integration: population evidence and mechanistic reasoning working together, each supplying what the other cannot. Individualized care requires both.