Hickam’s Dictum

Hickam’s Dictum counters the medical application of Occam’s Razor, reminding clinicians that patients can have multiple simultaneous conditions. Commonly phrased as “patients can have as many diseases as they damn well please”, the dictum advises caution against premature diagnostic closure based on parsimony alone.

While Occam’s Razor emphasises the simplicity of a single unifying diagnosis, Hickam’s Dictum reflects clinical reality, especially in older or comorbid patients, where overlapping or unrelated pathologies may coexist. Together, they form a complementary diagnostic heuristic: begin with simplicity, but remain open to complexity.

A man can have as many diseases as they damn well please

Attributed to Dr. John Hickam

Application: Hickam’s Dictum serves as a cognitive check against premature closure and diagnostic anchoring. It encourages clinicians to:

• Consider coexisting pathologies rather than forcing a unifying diagnosis.
• Remain open to diagnostic complexity, especially in patients with multiple comorbidities, atypical presentations, or unclear responses to treatment.
• Recognize that Occam’s Razor is a guide, not a rule—diagnostic elegance must yield to clinical reality.

Clinical Relevance: It is particularly applicable in:

• Elderly or polymorbid patients
• Complex or atypical clinical presentations
• Situations where a single diagnosis cannot explain all clinical findings

Examples:

• A patient with COPD exacerbation, pulmonary embolism, and pneumonia may present with dyspnea, each condition contributing in part.
• Coexistent lung cancer and asbestosis as independent causes of pulmonary symptoms.

Core Message: While Occam’s Razor seeks simplicity, Hickam’s Dictum embraces complexity. Both are tools, not dogmas, in clinical reasoning

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History of Hickam’s dictum

1998 – Wallace T. Miller published “Letter from the Editor” titled Occam versus Hickam in Seminars in Roentgenology, raising the contrast between diagnostic parsimony and multiple co‑morbidities. This appears to be the earliest documented English‑language publication explicitly naming “Hickam’s dictum.”

William of Occam stated…”Entia non sunt multiplicanda, praeter necissitatum.” In other words, things should not be multiplied unless necessary…Osler, took this principle, which he called Occam’s razor, and applied it to medicine. Osler stated that we should always try to fit all of a patient’s symptoms and clinical findings into one diagnosis…This helps us to make a unifying concept for a patient’s various problems.

On the other hand, not all findings can be neatly placed under the umbrella of a single diagnosis. This led to “Hickam’s dictum,” a concept elaborated by Hickam “A man can have as many diseases as he damn well pleases.” Daily, we are faced with the problem–should we place a particular finding under the aegis of Occam or Hickam. This is often a dilemma. In my experience, Hickam often triumphs.

 Miller 1998

2004 – The NEJM featured a clinical case discussion titled “Occam’s razor versus Saint’s Triad”. The case involved a 60-year-old immunosuppressed woman presenting with dyspnoea, ultimately diagnosed with both Pneumocystis jirovecii pneumonia and pulmonary embolism. The authors used this case to underscore the limitations of diagnostic parsimony and emphasized the clinical relevance of Hickam’s dictum, citing it as: “A patient can have as many diseases as he darn well pleases.”

This was one of the earliest mainstream medical publications to formally invoke Hickam’s dictum in contrast to Occam’s razor, cementing its place in the teaching of differential diagnosis.

2011 – Diagnostic Heuristics and Clinical Reasoning. Mani et al (2011) describe Hickam’s Dictum as a core balancing principle in differential diagnosis: “The dictum warns against over-reliance on Occam’s razor and is particularly useful in older patients and those with multiple comorbidities.”

Textbooks and reasoning frameworks emphasized its utility in avoiding diagnostic anchoring and premature closure, especially in emergency and internal medicine contexts .

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Associated Persons

• John Bamber Hickam (1914-1970)

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References

Historical references

• Miller WT. Occam versus Hickam. Seminars in Roentgenology 1998; 33(3): 213.
• Hilliard AA, Weinberger SE, Tierney LM Jr, Midthun DE, Saint S. Clinical problem-solving. Occam’s razor versus Saint’s Triad. N Engl J Med. 2004 Feb 5;350(6):599-603. 
• Mani N, Slevin N, Hudson A. What Three Wise Men have to say about diagnosis. BMJ. 2011 Dec 20;343:d7769

Eponymous term review

• Levine D, Bleakley A. Maximising medicine through aphorisms. Med Educ. 2012 Feb;46(2):153-62.
• Borden N, Linklater D. Hickam’s Dictum. West J Emerg Med. 2013 Mar;14(2):164.
• Freixa M, Simões AF, Rodrigues JB, Úria S, da Silva GN. Occam’s razor versus Hickam’s dictum: two very rare tumours in one single patient. Oxf Med Case Reports. 2019 May 31;2019(5):omz029.
• Stein H, Lowenstein EJ. Occam’s razor and Hickam’s dictum: a dermatologic perspective. Diagnosis (Berl). 2022 Nov 18;10(2):96-99.
• Blaser S, Schaye V, Hwang J, Cocks P, Kudlowitz D. Hickam’s dictum, Occam’s razor, and Crabtree’s bludgeon: a case of renal failure and a clavicular mass. Diagnosis (Berl). 2021 Aug 5;9(1):133-139.
• Aberegg SK, Poole BR, Locke BW. Hickam’s Dictum: An Analysis of Multiple Diagnoses. J Gen Intern Med. 2024 Oct 28