What’s the plural of “thesis”?
Thesis, (and its plural theses) is an example of one of the many common English words that has roots elsewhere. In this case, thesis is a word that has roots all the way back to Ancient Greek. Like other similarly structured words: diagnosis, synthesis, analysis, oasis, crisis, nemesis and the like, thesis is by no means the only frequently used Greek word that’s made it to Modern English.
My thesis is due next week.
The library archives contain many valuable theses on the subject.
The committee reviewed all the thesises before the defense.
The students submitted their thesis yesterday.
What’s the singular of thesis?
Thesis is a singular noun and refers to one thing (or one thesis).
What’s a thesis?
Merriam-Webster defines the noun thesis (plural theses) as follows, “a dissertation embodying results of original research and especially substantiating a specific view especially : one written by a candidate for an academic degree.”
Nouns that end in -sis/ses
Thesis is an irregular plural noun that does not end in the typical -s/-es that regular plural noun forms take. This is so despite that theses plural does in fact end in the conventional -s/-es suffix. Why is it still considered irregular; then, given that it follows the regular plural form? Notice the following regular plural noun forms:
Thesis/theses operates differently. With these Greek words, the -ses does not simply add onto the end of the singular form of the noun; instead, -ses replaces the singular noun’s suffixes, and effectively changes the entire spelling of the word (and arguably the word itself.)
| singular | plural |
| crisis | crises |
| diagnosis | diagnoses |
| oasis | oases |
| synopsis | synopses |
| thesis | theses |
Associate “thesis” with words like “analysis”; they follow the Greek pattern of changing “-sis” to “-ses” for the plural (“theses”, “analyses”).
Examples of “thesis” (singular) in sentences
His master thesis was on modal neural networks.
She wrote her thesis on Renaissance Nativity scenes.
We disagreed with the basic thesis of the report.
I’ve made a first draft of my thesis.
The student’s experiments helped her formulate a thesis to share with her professor and classmates.
Examples of “theses” (plural) in sentences
It must not be assumed that Luther’s ninety-five theses produced any considerable direct results.
The collection of theses are ready for publication.
Twenty years after Savonarola’s death Martin Luther made public his theses against indulgences.
Theses are generally examined by two or more specialists.
Theses is the plural form of the singular noun thesis.
Origin of the word “thesis”
Thesis/theses are of Greek origin.
Read about other irregular nouns
- What’s the plural of bison?
- What’s the plural of moose?
- What’s the plural of sheep?
- What’s the plural of ox?
- What’s the plural of cactus?
- What’s the plural of crisis?
- What’s the plural of hypothesis?
Read about other topics in grammar
Work Sheet
What is the correct plural form of the word “thesis”?
According to the blog post, which of the following words forms its plural in a similar way to “thesis”?
Is the plural form “theses” considered a regular or irregular plural noun according to the blog post?
Which of the following is the correct singular form of “theses”?
Which of these example sentences from the post uses the correct plural form?
The university library holds thousands of academic from past students.
My master’s is due next week.
The lab performs detailed of the chemical compounds.
The company faced several financial during the recession.
The book included brief of each chapter.
Frequently Asked Questions
What’s the correct plural of “thesis”?
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Is “thesises” a correct plural form?
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Why is “theses” an irregular plural noun?
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How do you use “thesis” and “theses”?
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Are other words pluralized like “thesis”?
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Yash, D. "What’s the Plural of Thesis? (Thesises? Theses?)." Grammarflex, Jun 20, 2025, https://www.grammarflex.com/whats-the-plural-of-thesis/.
Sources
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Merriam-Webster, thesis/theses.
