Diagnosis and Prognosis

Commonly Confused Words

diagnosis and prognosis
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The words diagnosis and prognosis are commonly (though not exclusively) used in the medical field. Both terms contain the root word gnosis, which means "knowledge." But diagnosis and prognosis refer to different kinds of knowledge or information.


The noun diagnosis refers to the process of analyzing information to understand or explain something. The plural of diagnosis is diagnoses. The adjective form is diagnostic.

The noun prognosis means a forecast or prediction--a judgment about what is likely to occur in the future. The plural of prognosis is prognoses.

In the medical field, diagnosis relates to identifying and understanding the nature of a disease or disorder, while a prognosis is a prediction of the probable outcome of a disease or disorder.


  • Medical researchers are examining strategies for the early diagnosis of Alzheimer's disease.
  • "A simple 15-minute brain scan could help doctors diagnose people* with autism by identifying structural differences in their brains. Scientists say the scans would speed up what is currently a long and emotional diagnostic procedure and allow the identification of at-risk children more rapidly."
    (Alok Jha, "Autism Can Be Diagnosed With Brain Scan--Study." The Guardian [UK], August 10, 2010)
    * See usage notes below. 
  • "The prognosis for continued and sustainable improvements in human well-being on a transformed planet Earth is, at best, guarded."
    (W.C. Clark et al., "Science for Global Sustainability." Earth System Analysis for Sustainability, ed. by Hans-Joachim Schellnhuber et al. MIT Press, 2004)
  • "Our task was to learn all that was known about the natural history of disease so that we could make an accurate diagnosis ​and a reasonably probabilistic prognosis. That done, our function as doctors would be to enlist the best possible nursing care, explain matters to the patient and family, and stand by."
    (Lewis Thomas, The Fragile Species. Touchstone, 1996)

    Usage Notes

    • "The distinguishing difference between diagnosis and prognosis is that prognosis implies the prediction of a future state. Thus, to accomplish prognosis requires both diagnostic and predictive tools, the former to sense the current state of damage and the latter to predict the future state based on projected usage and applicable life-prediction routines."
      (Materials Damage Prognosis, ed. by James M. Larsen et al., 2005) 
    • "The disease, not the patient, is diagnosed. Do not write 'She was diagnosed with cancer.' But also avoid stilted constructions like this: 'She was given a diagnosis of cancer.' Consider simpler alternatives: 'She learned she had cancer.' 'Tests showed she had cancer.' 'Her doctor told her she had cancer.'"
      (Allan M. Siegal and William G. Connolly, The New York Times Manual of Style and Usage, 5th ed. Three Rivers Press, 2015)
    • "Lurie 1927 disapproves of using the verb diagnose with a person as its object, even though there is often no other way of avoiding a stilted sentence. . . . [W]e believe that it is more frequently found in speech than in writing. However, the usefulness of this sense of diagnose is manifest, and its use in writing may well increase."
      (Merriam-Webster's Dictionary of English Usage, 1994)


      (a) When the ship's engine wouldn't start, the chief engineer offered a _____ of the problem.

      (b) The gloomy _____ for jobs and incomes in the coming year sent stock prices falling.

      Scroll down for answers.








      Answers to Practice Exercises: 

      (a) When the ship's engine wouldn't start, the chief engineer offered a diagnosis of the problem.

      (b) The gloomy prognosis for jobs and incomes in the coming year sent stock prices falling.