Few grammar questions spark as much debate and confusion as the difference between “theirs” and “their’s.” Whether you are drafting a professional email, writing an academic paper, or simply texting a friend, choosing the correct form is essential for clarity and credibility. This common confusion stems from a misunderstanding of how possessive pronouns function in the English language.
In this guide, you will learn the definitive rule for using these terms, why “their’s” is almost always a mistake, and how to master possessive pronouns once and for all. By the end of this article, you will possess the expertise to use these words with total confidence in any context.
Featured Snippet: The Quick Answer
“Theirs” is the only correct form; “their’s” is grammatically incorrect and should never be used. “Theirs” is a possessive pronoun that indicates ownership by a group previously mentioned. It does not require an apostrophe because it already inherently indicates possession, similar to words like “yours,” “ours,” and “hers.”
Comparison Table: At a Glance
| Feature | Correct Word | Incorrect Word |
| Spelling | Theirs | Their’s |
| Meaning | Belonging to them | N/A (Non-existent word) |
| Part of Speech | Possessive Pronoun | N/A |
| Grammar Rule | No apostrophe for possessive pronouns | Apostrophes denote contraction or possession of nouns |
| Correct Usage | “The house is theirs.” | N/A |
| Incorrect Usage | N/A | “The house is their’s.” |
| Memory Tip | Think of “yours” or “ours” | Avoid adding an apostrophe |
Defining “Theirs”
“Theirs” is a possessive pronoun. Its primary purpose is to replace a noun phrase to show ownership. Because it is a pronoun, it acts as a substitute for a specific group of people or things that you have already identified in your writing or speech.
For example, if you are discussing a set of keys belonging to a group of coworkers, you would say, “The keys are theirs.” You do not need to add an apostrophe because the word itself is already in its possessive form. It functions exactly like “his,” “hers,” “its,” “ours,” and “yours”—none of which ever take an apostrophe.
Key Differences and Usage
The confusion between “theirs” and “their’s” usually arises because people mistake possessive pronouns for possessive nouns. Here is how to distinguish between them:
- Possessive Pronouns (No Apostrophe): These words already express ownership. You never add an apostrophe to them.
- Examples: Mine, yours, his, hers, ours, theirs.
- Possessive Nouns (Apostrophe Required): When you are talking about a person or a thing (a noun) and you want to show they own something, you add an apostrophe.
- Examples: The teacher’s desk, the students’ books, the company’s policy.
Practical Examples:
- Correct: That car is theirs. (Correct use of possessive pronoun)
- Incorrect: That car is their’s. (Incorrect use of apostrophe)
- Correct: The owners’ car is parked outside. (Correct use of possessive plural noun)
The Fundamental Grammar Rule
The grammar rule is absolute: Possessive pronouns do not take apostrophes.
In English, the apostrophe generally serves two specific purposes: to show possession of a noun (John’s hat) or to indicate a contraction (it is = it’s). Because “theirs” is a pronoun—not a noun and not a contraction—the apostrophe has no place in the word. Adding one creates a grammatical error that confuses the reader and undermines your authority.
When to Use “Theirs”
Regardless of the setting, “theirs” is the only version of the word you should ever use.
- Academic and Professional Writing: Always use “theirs.” It is the standard form recognized by style guides like APA, MLA, and Chicago. Using “their’s” in a formal report or essay will be flagged as a spelling or grammar error.
- Business Communication: In emails and memos, clarity is paramount. “Theirs” keeps your communication professional.
- Informal Conversations and Social Media: Even in casual settings, “theirs” is the correct choice. Using “their’s” may make your writing appear unpolished.
Why People Make the Mistake
The error is highly common because English is inconsistent. We are taught early on that if something belongs to someone, we add an apostrophe and an ‘s’ (e.g., Sarah’s book). Because the brain likes patterns, we naturally try to apply that same rule to “their.” However, “their” is a pronoun, not a noun, and it follows the same irregular pattern as “yours” and “ours.” The urge to add an apostrophe is an attempt to force the word into a rule that simply does not apply to it.
Original Examples
- After the vote was counted, the final decision was clearly theirs.
- The trophy on the mantle is theirs, as they won the championship last night.
- Are these backpacks yours, or are they theirs?
- The responsibility for the project outcome is theirs alone.
- All the complaints in the suggestion box were theirs.
- If the decision is theirs to make, we should step back.
- The house at the end of the street is theirs.
- I thought the idea was mine, but it turned out to be theirs.
- Their parents are kind, but the children are even kinder than theirs.
- The victory is theirs to celebrate.
- Keep your comments to yourself; this fight is theirs, not ours.
- The data results were theirs to present at the conference.
- Everyone agreed the mistake was theirs to own.
- Those seats are theirs, so please do not sit there.
- Whether the dog is truly theirs remains a mystery.
The “Pronoun Rule” Memory Trick
To remember this forever, simply compare “theirs” to “yours” and “ours.”
Whenever you feel the urge to write “their’s,” ask yourself: “Do I write ‘your’s’ or ‘our’s’?” The answer is always no. Since you know that “yours” and “ours” never take an apostrophe, you can logically conclude that “theirs” never takes one either. If you don’t add an apostrophe to “yours,” don’t add one to “theirs.”
Mini Quiz: Test Your Knowledge
- Which is the correct spelling?
a) Their’s
b) Theirs
c) There’s
Answer: b - Identify the error: “The laptop on the desk is their’s.”
a) The laptop
b) on the desk
c) their’s
Answer: c - Which sentence is written correctly?
a) The success is theirs.
b) The success is theirs.
c) The success is theirs’.
Answer: a - Possessive pronouns take an apostrophe when?
a) Always
b) Only at the end of a sentence
c) Never
Answer: c - Is “theirs” a noun or a pronoun?
a) Noun
b) Pronoun
c) Verb
Answer: b
Frequently Asked Questions (FAQs)
Is “their’s” ever correct in British English?
No. There is no dialect of English, including British, American, Australian, or Canadian, where “their’s” is considered correct. It is universally recognized as a grammatical error. Always stick to the standard spelling: “theirs.”
What is the difference between “their,” “there,” and “theirs”?
“Their” is a possessive adjective (e.g., “their car”). “There” refers to a place or existence (e.g., “it is over there”). “Theirs” is a possessive pronoun used to replace a noun (e.g., “the car is theirs”). They are distinct words with specific roles.
Why do I see “their’s” used online sometimes?
You may see it on social media or in informal text messages because it is a common mistake. Many people assume that adding an apostrophe is the correct way to show possession for all words. It is an error born of a misunderstanding of English grammar rules.
Should I use “theirs” for singular people?
Yes. In modern English, “theirs” is frequently used as a gender-neutral singular pronoun to refer to a person whose gender is unknown or who uses they/them pronouns. It is perfectly acceptable and grammatically correct in both formal and informal contexts.
Does “theirs” need an apostrophe if it is plural?
No. The word “theirs” is already plural in nature because it refers to multiple owners. Adding an apostrophe—whether the owners are singular or plural—is always incorrect. The spelling never changes regardless of the number of people involved.
Can I use “theirs” in a formal legal document?
Absolutely. “Theirs” is the correct, standard English term. In legal or formal writing, precision is required, and using the correct pronoun is essential for maintaining the integrity of the document. “Theirs” is the only version accepted in formal registers.
Key Takeaways
- Theirs is the only correct spelling.
- Theirs is always incorrect.
- Possessive pronouns (mine, yours, hers, theirs) never take an apostrophe.
- Use “theirs” to replace a noun to indicate ownership.
- Remember the “yours/ours” rule to avoid the common apostrophe trap.
Conclusion
Mastering the distinction between “theirs” and “their’s” is a simple but powerful way to improve your writing. By remembering that “theirs” is a possessive pronoun that never requires an apostrophe, you avoid one of the most common errors in the English language.
Regardless of whether you are writing an academic thesis or a quick note, always use “theirs” to ensure your message is clear, professional, and grammatically precise. When in doubt, compare it to “yours” or “ours,” and you will always choose correctly.
I’m Julian Mercer, an English language writer dedicated to helping people master grammar through practical examples and clear explanations. I enjoy teaching grammar in a way that is both engaging and easy to remember.
My work focuses on grammar rules, punctuation, word usage, and writing techniques that readers can apply in everyday life. I believe learning English should be simple, enjoyable, and useful.
Books
English Grammar in Practice
Writing with Precision
Nathan Whitmore
Claire Holloway