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What’s the Plural of Thesis? (Thesises? Theses?)

Thesis, which means "proposition", and derives from Greek, is a singular noun. The plural of thesis is theses.

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.

What’s the singular of thesis?

"Thesis" singular in sentences.

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:

Regular nouns (end in –s/-es). By Gflex on Canva.

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.)

Greek nouns in English. Chart made by Gflex.

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

Read about other topics in grammar


  1. Merriam-Webster, thesis/theses.

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