'Diagnosis' vs. 'Prognosis'

They occur alphabetically, literally and figuratively.
What to Know

A diagnosis is an identification of a disease via examination. What follows is a prognosis, which is a prediction of the course of the disease as well as the treatment and results. A helpful trick is that a diagnosis comes before a prognosis, and diagnosis is before prognosis alphabetically. Additionally, diagnosis and detection both start with "d" whereas prognosis and prediction both start with "p."


As both are medical terms with similar roots, they are often easy to confuse.

"I'd rather live my life, when I can still walk around and do the things I want to do, than sit in a doctor's office," she said. "If they could give me a more hopeful diagnosis, then I may consider it harder." Her doctors now estimate that she may have a year to live without treatment.
— Mary Hynes, The Las Vegas Review-Journal, 21 Oct. 2019

An international team of pathologists has identified a new protein often found on pleural mesothelioma tumor cells. The discovery could lead to a more accurate prognosis for patients and future treatment advances.
Asbestos.com, 19 Dec. 2019

MEDCOM is a 5G-enabled telemedicine device that enables doctors to offer consultation to patients remotely. The portable device provides real-time, high-quality, and ultra-reliable clinical, physiological, and diagnostic information to doctors to make an accurate prognosis from a distance.
Vernonchan.com, 23 Jan. 2020

Janet's initial prognosis, after returning to L.A., was a viral syndrome. She was later admitted to an ICU, where she tested positive for the Coronavirus. She is now stable, but being treated for severe pneumonia.
Extratv.com, 13 Mar. 2020

We're going to diagnose—that is, identify for you—the issue with the above sentences and prescribe how to alleviate it. Our diagnosis is a confusion with the words diagnosis and prognosis. Our prognosis is not very hopeful, mainly because diagnosis and prognosis are both medical terms and they derive from similar roots, which means, in the minds of quite a few people, they are likely compartmentalized together. As a last resort, however, we prescribe reading this article to learn, or relearn, the key Latin and Greek roots of the terms in the hope that it will help differentiate them. In prep, the main difference is temporal: a diagnosis involves on-site examination and a prognosis is a prediction of what's to come.

The Origins of 'Diagnosis' and 'Prognosis'

Gno and gni are Latin and Greek roots found in words with the basal meaning of "to know." In Latin, for example, the word for "to get/come to know" is gnōscere; in Greek, it is gignōskein. The roots run to English's verb know. Other rooted words you may recognize (which itself is a word meaning "to know again") and some you may be ignorant of (meaning "to not know"). In addition to the two just mentioned, there is agnostic, cognitive, incognito, and—yes—diagnosis and prognosis, among others.

'Diagnosis' vs. 'Prognosis'

As you are aware, people sometimes confuse diagnosis and prognosis. Since time is of the essence: diagnosis is used to identify a present disease, illness, problem, etc., by examination and observation (of signs and symptoms); prognosis refers to predicting the course of the diagnosed disease, illness, problem, etc., and determining treatment and outcome. To be clear, the prognosis comes after the diagnosis; a diagnosis precedes a prognosis.

After the session, the psychiatrist gave a diagnosis of ADHD.

The doctor's prognosis was promising. She mentioned complete recovery in a couple of months, but she also informed us that much depends on the test results.

Knowing the meaning of the ancient roots is certainly beneficial in this case as well as for overall vocabulary building. The prefix dia- can mean "through," "during," or "across," so diagnosis can be thought of as a recognition of a disease during examination or observation. Having the prefix pro-, meaning "before," prognosis essentially means "knowledge beforehand" and, by extension, it is used to indicate how a situation is likely to turn out.

Prognosis was originally a medical term for the doctor's prognostication, but the word soon broadened in meaning to include predictions made by experts of all kinds. Thus, for example, economists offer prognoses (notice the irregular plural form—the plural of diagnosis is diagnoses) about where the economy is going, and climate scientists prognosticate about the effects of global warming. Similarly, diagnosis is applied outside of medicine—for example, you might run a computer diagnosis.

Tricks for Remembering 'Diagnosis' and 'Prognosis'

Our Rx: mnemonics. The letter d comes before p in the alphabet so a diagnosis comes before a prognosis. Diagnosis occurs on the day of the doctor's visit and is a determination/detection/discovery of a disease. Prognosis is a prediciton/prophecy of what's to come, concerning progression of the disease and its outcome, post-visit.

Drop Image by Venngage Infographic Maker.