Plural of Diagnosis
“Diagnosis” forms the irregular plural “diagnoses.” The spelling change is easy to miss because “diagnoses” is also visually close to a verb form from “diagnose.” In noun use, context and agreement identify the plural: one diagnosis, several diagnoses.
The plural of “diagnosis” is “diagnoses.” The ending changes from -sis to -ses, and the final syllable is pronounced differently from the singular.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| one judgment/identification | diagnosis | Use the singular noun. |
| two or more | diagnoses | Use the irregular plural. |
| medical advice or evaluation | outside this grammar guide | The page addresses form, not diagnosis itself. |
Quick tests
Plural-choice test
Are you naming more than one diagnosis?
If yes: Use “diagnoses.”
If no: Use singular “diagnosis” for one; if the word is a verb, follow the verb “diagnose.”
Caveat: The page explains noun number and pronunciation only; it does not evaluate or interpret medical conditions.
Examples
The report lists three diagnoses.
“Diagnoses” is the plural noun.
Her diagnosis was revised after further testing.
One instance takes singular “diagnosis.”
The two diagnoses require separate documentation.
A plural quantity triggers the irregular plural form.
Further guidance
Core difference
Use “diagnosis” for one and “diagnoses” for more than one.
Fast Test
If a number or plural determiner precedes the noun, use “diagnoses.” If the word is acting as a verb, analyze it under “diagnose,” not this noun rule.
Usage Boundary
Do not confuse the plural noun “diagnoses” with a verb form purely from spelling, and do not expand the page into clinical guidance.
Sources and evidence
Sources are shown with the role they play in this guide. Historical or style-sensitive claims are kept within the evidence boundary described above.
- DIAGNOSIS | English meaning - Cambridge Dictionary (opens in a new tab)Cambridge University Press · Cambridge gives diagnoses as the plural of diagnosis, supporting the irregular -is to -es form and pronunciation change.