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 form the plural. Instead, it follows a pattern borrowed from Greek, where the singular ending "-is" changes to "-es" in the plural. You would say "one thesis" but "two theses."
Quick Answer: Thesis vs. Theses
| Form | Word | Example |
|---|---|---|
| Singular | Thesis | My thesis is about climate change. |
| Plural | Theses | The students submitted their theses last week. |
If you are talking about one long research paper or argument, use thesis. If you are talking about more than one, use theses. This rule applies in both formal academic writing and everyday conversation.
Why Is the Plural "Theses" and Not "Thesises"?
The word thesis comes from Greek, and English has kept the original Greek plural pattern for many words ending in "-is." Other common examples include:
- Crisis becomes crises (not crisises).
- Hypothesis becomes hypotheses (not hypothesises).
- Analysis becomes analyses (not analysises).
- Parenthesis becomes parentheses (not parenthesises).
This pattern is consistent in academic and formal English. Using "thesises" is always incorrect, even in informal settings.
Formal vs. Informal Use
Formal Contexts (Academic Writing, Emails to Professors, Reports)
In formal writing, you must use the correct singular and plural forms. Mistakes here can make your work look careless.
- Correct (formal): "The committee will review each thesis individually."
- Correct (formal): "All theses must be submitted by Friday."
- Incorrect (formal): "The committee will review each theses individually." (Using the plural form for a singular subject.)
Informal Contexts (Conversation, Text Messages, Casual Emails)
Even in casual conversation, native speakers rarely make mistakes with this word. You will hear:
- "I'm still working on my thesis." (Singular)
- "How many theses did you have to write for your master's?" (Plural)
Using "thesises" in any context will sound unnatural and incorrect.
Comparison Table: Thesis vs. Theses
| Feature | Thesis (Singular) | Theses (Plural) |
|---|---|---|
| Number | One | More than one |
| Pronunciation | THEE-sis | THEE-seez |
| Common usage | Refers to a single research paper or central argument. | Refers to multiple research papers or arguments. |
| Grammar agreement | Use singular verbs: "The thesis is…" | Use plural verbs: "The theses are…" |
| Example | Her thesis explores renewable energy. | Their theses cover different topics. |
Natural Examples
Here are examples of how thesis and theses appear in real writing and conversation:
In Academic Writing
- "The central thesis of this book is that economic growth does not always lead to happiness."
- "Several doctoral theses have been written on this subject in the last decade."
- "My thesis advisor helped me refine my research question."
In Email Communication
- To a professor (formal): "Dear Dr. Lee, I am attaching my thesis for your review."
- To a colleague (informal): "Hey, can you send me the theses from last year's graduates? I want to see their methodology."
In Everyday Conversation
- "I'm so relieved my thesis is finally done."
- "How many theses did your department approve this semester?"
Common Mistakes
Even advanced English learners sometimes make these errors. Here are the most frequent ones:
Mistake 1: Using "Thesises"
Incorrect: "The students wrote three thesises."
Correct: "The students wrote three theses."
Why: "Thesises" is not a word in English. Always use "theses" for the plural.
Mistake 2: Using "Theses" as a Singular
Incorrect: "My theses is about ancient history."
Correct: "My thesis is about ancient history."
Why: "Theses" is plural, so it cannot be used with a singular verb or possessive pronoun like "my."
Mistake 3: Confusing "Thesis" with "Theses" in Subject-Verb Agreement
Incorrect: "The thesis are due next week."
Correct: "The thesis is due next week." or "The theses are due next week."
Why: The verb must match the number of the subject.
Mistake 4: Mispronouncing the Plural
Incorrect pronunciation: THEE-sis (for plural)
Correct pronunciation: THEE-seez (for plural)
Why: The vowel sound changes in the plural form. The "i" in "thesis" sounds like "ih," while the "e" in "theses" sounds like "ee."
Better Alternatives and When to Use Them
While thesis and theses are the correct terms, there are times when a different word might be more appropriate depending on the context.
| Word | When to use it | Example |
|---|---|---|
| Dissertation | Often used interchangeably with "thesis" in some countries, but in the US, a dissertation is usually for a doctorate, while a thesis is for a master's. | "She defended her dissertation last month." |
| Paper | A more general term for a shorter academic work or article. | "I'm writing a paper for my history class." |
| Essay | A shorter, often less formal piece of writing on a single topic. | "The essay argues for stricter environmental laws." |
| Argument | Refers to the central claim or idea, not the written document itself. | "The main argument of the book is compelling." |
| Proposition | A formal statement or idea put forward for consideration, often in logic or philosophy. | "His proposition challenges traditional views." |
When to use "thesis": Use it when you are specifically referring to a long, formal research paper submitted for a degree, or to the central argument of any written work. It is the most precise term in academic contexts.
Mini Practice: Thesis or Theses?
Choose the correct word (thesis or theses) for each sentence. Answers are below.
- She is working on her _____ about marine biology.
- The library has a collection of over 500 doctoral _____.
- Both of my _____ were well-received by the faculty.
- His _____ focuses on the effects of social media on teenagers.
Answers
- Thesis (singular, referring to one paper)
- Theses (plural, referring to many papers)
- Theses (plural, referring to two papers)
- Thesis (singular, referring to one paper)
Frequently Asked Questions
1. Is it correct to say "thesis paper"?
Yes, it is common to say "thesis paper" to emphasize that you are talking about the written document. For example, "I need to print my thesis paper." However, "thesis" alone is usually sufficient.
2. What is the plural of "master's thesis"?
The plural is "master's theses." For example: "The department published three master's theses this year." Note that "master's" stays singular because it describes the type of thesis.
3. Can "thesis" mean something other than a research paper?
Yes. "Thesis" can also mean a central argument or idea in any piece of writing or speech. For example: "The thesis of his speech was that education should be free." In this case, the plural is still "theses."
4. How do I remember the difference between "thesis" and "theses"?
Think of other words that follow the same pattern: "crisis" becomes "crises," and "analysis" becomes "analyses." The "-is" to "-es" change is a signal that the word is plural. Also, remember that "thesis" has one "s" at the end (like "is" for singular), while "theses" has "ses" (like "are" for plural).
Final Tip for Learners
When you are writing, always double-check the number of the subject. If you are talking about one idea or paper, use thesis. If you are talking about two or more, use theses. This small habit will make your academic English much more accurate and professional. For more help with similar words, explore our guides on Common Plural Forms and Confusing Plurals. If you have further questions, feel free to visit our FAQ page or contact us.
