Plural of Thesis
“Thesis” forms the irregular plural “theses.” The spelling and pronunciation both change, so the safest pattern is to learn the pair directly: one thesis, two theses.
The plural of “thesis” is “theses.” The ending changes from -is to -es, and the final syllable is pronounced differently.
Key details
Choose the right form
| Meaning / situation | Form / construction | Decision |
|---|---|---|
| one dissertation/proposition | thesis | Use the singular. |
| two or more | theses | Use the irregular plural. |
| attempted regular ending | thesises | Avoid it. |
Quick tests
Plural-choice test
Are you naming more than one thesis?
If yes: Use “theses.”
If no: Use singular “thesis.”
Caveat: The plural has a pronunciation change as well as a spelling change.
Examples
The library holds several doctoral theses.
“Theses” is the plural noun.
Her thesis examines urban migration.
One takes singular “thesis.”
The two theses reach different conclusions.
A plural quantity takes “theses.”
Further guidance
Core difference
Use “thesis” for one and “theses” for more than one.
Fast Test
If a number greater than one modifies the noun, choose “theses.”
Usage Boundary
Do not form the plural as “thesises.”
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.
- THESIS | English meaning - Cambridge Dictionary (opens in a new tab)Cambridge University Press · Cambridge gives theses as the plural of thesis and records the changed pronunciation.