Is Thesis Singular or Plural?
The word thesis is singular. Its plural form is theses. This is a common point of confusion because the word does not follow the standard English rule of adding an “-s” or “-es” to make a noun plural. Instead, it changes its ending from “-is” to “-es.” If you are writing about one argument or research paper, use thesis. If you are writing about two or more, use theses.
Quick Answer: Thesis vs. Theses
| Form | Number | Example |
|---|---|---|
| Thesis | Singular | Her thesis on climate change was well received. |
| Theses | Plural | The library holds over fifty doctoral theses. |
Why Is the Plural of Thesis Not “Thesises”?
The word thesis comes from Greek. In English, many words borrowed from Greek or Latin keep their original plural patterns. For nouns ending in “-is,” the plural is formed by changing the “-is” to “-es.” Other examples include crisis (crises), analysis (analyses), and hypothesis (hypotheses). This rule is consistent, so once you learn it, you can apply it to similar words.
When to Use “Thesis” (Singular)
Use thesis when you are referring to one main idea, argument, or a long piece of academic writing. It works in both formal and informal contexts, though it is most common in academic, professional, or serious discussion settings.
Formal and Informal Contexts
- Formal (academic writing, email to a professor): “My thesis examines the economic effects of remote work.”
- Informal (conversation with a classmate): “I still haven’t picked a thesis for my history paper.”
Natural Examples (Singular)
- Each student must submit a thesis by the end of the semester.
- The central thesis of the article is that education reform is urgent.
- She defended her thesis in front of three professors.
- His thesis was too broad, so he narrowed it down.
When to Use “Theses” (Plural)
Use theses when you are talking about more than one thesis. This could mean multiple research papers, multiple main arguments, or multiple ideas from different sources.
Formal and Informal Contexts
- Formal (email to a department head): “The theses submitted this year cover a wide range of topics.”
- Informal (conversation with a friend): “I read two theses last night, and both were interesting.”
Natural Examples (Plural)
- The university publishes the best theses online every year.
- Several theses from the 1990s are still cited today.
- We compared the main theses of three different philosophers.
- Graduate students often spend months revising their theses.
Common Mistakes with Thesis and Theses
Even advanced English learners sometimes make errors with these words. Here are the most frequent mistakes and how to avoid them.
Mistake 1: Using “Thesises” as the Plural
This is the most common error. Because most English nouns add “-s” or “-es,” learners often write thesises. This is incorrect. Always use theses for the plural.
Incorrect: He wrote three thesises during his PhD.
Correct: He wrote three theses during his PhD.
Mistake 2: Using “Thesis” for Multiple Items
Some writers forget to change the form at all and use thesis for both singular and plural. This can confuse readers.
Incorrect: The professors reviewed every thesis from last year.
Correct: The professors reviewed every thesis from last year. (If one at a time)
Correct: The professors reviewed all the theses from last year. (If multiple)
Mistake 3: Confusing “Thesis” with “Hypothesis”
These words are related but not interchangeable. A thesis is a statement or argument that you defend. A hypothesis is a testable prediction. Both follow the same plural rule (hypotheses), but their meanings differ.
Incorrect: My thesis is that the drug will reduce symptoms. (Use hypothesis for a testable prediction.)
Correct: My hypothesis is that the drug will reduce symptoms.
Better Alternatives and When to Use Them
Depending on the context, you might choose a different word instead of thesis or theses. Here are some alternatives and when they fit better.
| Word | When to Use | Example |
|---|---|---|
| Argument | In casual conversation or writing about a main point | Her main argument was that taxes should be lower. |
| Claim | When stating something that needs evidence | The author’s claim is not supported by data. |
| Dissertation | Specifically for a long doctoral research paper | He finished his dissertation in three years. |
| Paper | General term for a written academic work | I have to submit a paper by Friday. |
| Essay | For shorter, less formal academic writing | She wrote a short essay on pollution. |
Use thesis when you want to sound precise and academic. Use argument or claim in everyday conversation or informal writing. Use dissertation only for doctoral-level work.
Comparison Table: Thesis vs. Theses
| Feature | Thesis (Singular) | Theses (Plural) |
|---|---|---|
| Number | One | Two or more |
| Pronunciation | /ˈθiː.sɪs/ | /ˈθiː.siːz/ |
| Common context | Academic paper, main argument | Multiple papers, multiple arguments |
| Example sentence | This thesis is well organized. | These theses are well organized. |
| Verb agreement | Singular verb (is, was, has) | Plural verb (are, were, have) |
Mini Practice: Thesis or Theses?
Choose the correct form for each sentence. Answers are below.
- She is working on her ________ about renewable energy.
- The library has a collection of old ________ from the 1800s.
- Both ________ present strong evidence for their claims.
- His ________ was rejected because it lacked original research.
Answers
- thesis (singular, one paper)
- theses (plural, multiple papers)
- theses (plural, two or more)
- thesis (singular, one paper)
Frequently Asked Questions (FAQ)
1. Is “thesis” ever used as a plural?
No. In standard English, thesis is always singular. Using it as a plural is a grammatical error. Always use theses for more than one.
2. How do you pronounce “theses”?
The plural theses is pronounced with a long “e” sound at the end: /ˈθiː.siːz/. It rhymes with “seas” or “freeze.” The singular thesis ends with a short “i” sound: /ˈθiː.sɪs/.
3. Can I use “thesis” in an email to my boss?
Yes, if you are referring to a main argument or a formal document. For example: “The thesis of my report is that we need better training.” It is appropriate in professional emails.
4. What is the difference between “thesis” and “dissertation”?
In many countries, a thesis is written for a master’s degree, while a dissertation is written for a doctorate. However, usage varies by region. In the United States, a dissertation is usually for a PhD, and a thesis is for a master’s. In the UK, it is often the opposite. Check your institution’s guidelines.
Final Tip for Learners
To remember the plural of thesis, think of other words that end in “-is” and change to “-es.” Practice with crisis (crises), analysis (analyses), and hypothesis (hypotheses). Once you see the pattern, it becomes natural. Use thesis for one and theses for more than one, and you will always be correct.
For more help with similar questions, visit our Singular or Plural Checks section. You can also explore Common Plural Forms or Plural Spelling Rules for additional guidance. If you have further questions, check our FAQ page or contact us directly.
