Generating and Selecting Diagnostic Hypotheses
Donald E. Stanley, Maine Medical Center, Department of Pathology, Portland, Maine.
Rune Nyrup, Durham University, Department of Philosophy
Francis Bacon: ‘shake out the folds of nature’ ‘twist the lion’s tail’
Charles Darwin: “ I think that I have become a little more skillful in guessing right explanations and in devising experimental tests; but this may probably be the result of mere practice, and of a large store of knowledge.”
  1. Introduction:
Clinical diagnostic medicine is an experimental science based on observation, hypotheses, and testing. It is a dynamic process that involves skills in history taking, observation, diagnostic conjectures and testing, possibly leading to new or revised conjectures. For the clinician, it is always a reflexive process subject to revision. In this article, we want to provide experiential insight into the logic of this diagnostic process.
Our aim is to describe the logic of medical diagnosis as it is practiced in clinical medicine recognizing the pragmatics of diagnosis. We primarily aim to describe (rather than prescribe) the structures and patterns of reasoning used by experienced clinicians under different diagnostic circumstances and how these patterns of inquiry allow further insight into the evaluation and proposed treatment of patients. We however start by introducing a general account of the logic of medical diagnosis in order to focus our analysis of a detailed clinical case. So first things first . . .
  1. The Logic of Medical Diagnosis
The process of diagnosis consists of three types of reasoning: (1) generation of a plausible diagnostic hypotheses, or abduction; (2) selection and prioritization of hypotheses for further testing; (3) acceptance or rejection of diagnoses. Although these are in practice often overlapping or intertwining processes, they can be distinguished logically.
The first type refers to the process of eliminating implausible diagnoses and generating plausible diagnoses after observing and considering a patient’s previous history, presenting condition, signs, and symptoms. The diagnostic process begins with an abductive search for the differential diagnosis. Charles Peirce observed that this process has a logical form, namely:
The surprising fact, C, is observed.