mind & bodyanalysisWellcome Collection
Doctors reason like detectives by arguing backwards from clues to the most likely cause
Doctors and detectives both work by spotting clues, forming hypotheses and testing them. Much of their reasoning is abduction, which starts from observations and works backwards to the most probable explanation. A doctor who sees a stiff, stooped posture, a scuffed shoe and a black eye may recognise Parkinson's disease, since the symptoms fit the disease better than any other cause. Absences matter too: a normal leg makes a stroke unlikely. Good diagnosticians then list rival explanations before settling on one, a step called differential diagnosis. The model for Sherlock Holmes was Joseph Bell, a surgeon who taught Arthur Conan Doyle at Edinburgh.
Abduction runs from observed facts back to the explanation that best accounts for them, rather than forward from a rule to a certain result. Doctors list the possible causes, then test each by asking which would also explain the absence of other signs. Differential diagnosis formalises this by ruling out alternatives one at a time.
The comparison shows how medical diagnosis is a form of structured reasoning under uncertainty. Real patients are messier than fictional cases, so clinicians must avoid fitting the facts to their first idea.
Medical reasoning and detective fiction have long shared methods, and early forensic science drew on the same clinical observation. Modern diagnosticians still use checklists and tests to counter the bias of fitting facts to a favourite hypothesis.
Arthur Conan Doyle trained as a doctor before he wrote the Sherlock Holmes stories.
Wellcome Collection · CC BY 4.0
Illustrative photo · J.M.E. Saxby, Public domain, via Wikimedia Commons
