Quick Answer: The correct form is theirs, not their’s. “Theirs” is a possessive pronoun used to show that something belongs to two or more people, while “their’s” is an incorrect spelling. The confusion usually happens because possessive forms such as “John’s” contain an apostrophe, but possessive pronouns such as “theirs” do not.
The incorrect form their’s is created by applying the apostrophe rule used with possessive nouns to a possessive pronoun. That mistake is understandable because English uses apostrophes in forms such as “Sarah’s book” and “the students’ classroom.” However, possessive pronouns follow their own pattern. Words such as “yours,” “ours,” “hers,” “theirs,” and “its” do not normally take apostrophes.
This small spelling difference can create real mistakes in academic writing, workplace communication, proofreading, and online content. Understanding the rule makes the choice much easier.
Theirs vs Their’s: What’s the Difference?
The key difference is simple: theirs is correct, while their’s is incorrect in standard English.
The word theirs is a possessive pronoun. It indicates that something belongs to a group of people or to people whose gender is unspecified or intentionally not identified.
For example:
“The blue office is theirs.”
“The decision was theirs.”
“The responsibility is theirs.”
In each sentence, “theirs” replaces a longer noun phrase such as “the employees’,” “the committee’s,” or “their group’s.”
The form their’s is not a standard English possessive pronoun. Although it may appear in informal online writing, personal messages, or content written by learners, it is considered an incorrect spelling in standard English.
Mini Recap
Use theirs when something belongs to two or more people.
Do not add an apostrophe to theirs.
Their’s is not the standard possessive form.
The correct sentence is “The house is theirs,” not “The house is their’s.”
Is Theirs vs Their’s a Grammar, Vocabulary, or Usage Issue?
This is primarily a grammar and usage issue, with a spelling component.
The two forms are not interchangeable. In standard English, theirs is the established possessive pronoun. Their’s does not function as an accepted alternative.
The distinction becomes especially important because English has several different ways of expressing possession. A possessive noun can use an apostrophe, as in “James’s laptop.” A plural noun can also use an apostrophe, as in “the teachers’ lounge.” However, possessive pronouns have a separate pattern.
Consider these examples:
“This is the teacher’s desk.”
“This desk is theirs.”
The first sentence uses a possessive noun. The second uses a possessive pronoun. The apostrophe belongs in the first example but not the second.
In academic writing, formal correspondence, business documents, and edited publications, theirs should always be used. In casual digital communication, you may encounter their’s, but its appearance does not make it grammatically standard.
How to Use Theirs Correctly
Theirs is normally used when the noun being possessed has already been mentioned or is obvious from context. It prevents unnecessary repetition.
Instead of writing:
“The employees chose the employees’ preferred design.”
You can write:
“The employees chose theirs.”
Here, “theirs” stands in for something belonging to the employees.
Workplace Example
“The marketing team submitted its proposal, but the final design was theirs.”
A clearer example is:
“We reviewed the two proposals and selected theirs.”
In this sentence, “theirs” refers to the proposal belonging to the other group.
Academic Example
“The researchers compared their results with those of another team and found that the conclusions were similar to theirs.”
Here, “theirs” replaces “the other team’s conclusions.”
Technology Example
“The developers tested our application against theirs.”
In this sentence, “theirs” refers to an application belonging to another company or development team.
Usage Recap
Use theirs when the owner has already been identified or can be understood from context. It is especially useful when you want to avoid repeating a noun.
How to Use Their Correctly
Although their and theirs are closely related, they do not perform exactly the same grammatical job.
Their is a possessive determiner. It normally appears before a noun.
Examples include:
“Their house is large.”
“Their project was successful.”
Notice that “their” needs a noun after it in these examples.
By contrast, theirs is a possessive pronoun and normally stands independently.
Compare:
“This is their car.”
“This car is theirs.”
Both sentences express possession, but the grammatical structure is different.
Workplace Example
“Their department handles customer support.”
Here, “their” comes before “department.”
Academic Example
“Their research provides useful evidence.”
Again, “their” modifies the noun “research.”
Technology Example
“Their platform offers several useful features.”
The word “their” describes whose platform it is.
Usage Recap
Use their before a noun.
Use theirs when the possessed noun does not need to be repeated.
Never change theirs into their’s simply because an apostrophe appears in other possessive forms.
When You Should NOT Use Theirs or Their’s
There are several situations where writers commonly make mistakes with these forms.
1. Do not write their’s as the possessive pronoun
Incorrect:
“The red car is their’s.”
Correct:
“The red car is theirs.”
2. Do not use theirs directly before a noun
Incorrect:
“Theirs house is beautiful.”
Correct:
“Their house is beautiful.”
3. Do not replace their with theirs before a noun
Incorrect:
“Theirs project received an award.”
Correct:
“Their project received an award.”
4. Do not add an apostrophe because you hear a possessive meaning
Possession does not automatically require an apostrophe. The form theirs is already possessive.
5. Do not treat theirs like a possessive noun
You would write “the company’s policy,” but you would write “the policy is theirs.”
6. Do not assume every possessive form follows the same pattern
English possessive forms are not completely uniform. “John’s” and “theirs” follow different grammatical patterns.
7. Do not use their’s in formal writing
Even if readers understand the intended meaning, the spelling is considered incorrect in standard edited English.
8. Do not confuse theirs with there’s
“There’s” is a contraction of “there is” or “there has.” It has a completely different meaning from “theirs.”
Common Mistakes and Correct Usage
Decision Rule Box
If a noun comes immediately after the word, use their.
Example: “Their proposal was accepted.”
If the possessive word stands alone, use theirs.
Example: “The proposal was theirs.”
If you are considering their’s, remove the apostrophe.
The correct form is theirs.
Theirs and Their’s in Modern Technology and AI Tools
Modern technology has made this distinction more visible because grammar checking tools, word processors, search systems, and AI writing assistants frequently identify incorrect possessive forms.
A sentence such as “The account is their’s” may be flagged by a grammar checker because the apostrophe does not belong in the standard possessive pronoun. AI writing systems can also recognize the grammatical relationship when generating or revising text.
However, automated tools should not replace grammatical understanding. A writer who knows the rule can recognize the correct form even when software is unavailable.
This matters in professional websites, software documentation, academic papers, user interfaces, reports, and business communication, where small language errors can affect perceived accuracy.
The Etymology Behind Theirs
The word theirs developed from the possessive form associated with they. English possessive pronouns have developed over time as the language changed its pronoun system.
The modern forms “their” and “theirs” are related, but they developed different grammatical functions. “Their” became the possessive determiner used before nouns, while “theirs” became the independent possessive pronoun.
The apostrophe in their’s is therefore not part of the historical standard form.
An Expert Style Explanation
A useful way to remember the rule is this:
“Possessive pronouns such as theirs express ownership without needing an apostrophe.”
This principle also helps with other possessive pronouns. Compare “our” with “ours,” “your” with “yours,” and “their” with “theirs.”
Two Practical Case Studies
Case Study 1: Academic Editing
Imagine a university student writing:
“The final results were their’s.”
During proofreading, the sentence is corrected to:
“The final results were theirs.”
The correction removes the apostrophe and makes the sentence conform to standard academic English. The meaning remains unchanged, but the grammatical accuracy improves.
Case Study 2: Business Communication
Consider a workplace comparison:
“Our proposal was approved, but their’s was rejected.”
A polished version reads:
“Our proposal was approved, but theirs was rejected.”
The revision removes an unnecessary apostrophe while preserving the intended contrast. In professional communication, such corrections help maintain consistent editorial standards.
Error Prevention Checklist
Always use theirs when:
- You mean something belongs to them.
- The possessive word stands independently.
- The noun being possessed is already understood.
- You are writing formal, academic, or professional English.
Never use their’s when:
- You are using the independent possessive pronoun.
- You mean “belonging to them.”
- You are writing edited or formal English.
- You are replacing a previously mentioned noun phrase.
Related Grammar Confusions You Should Master
Once you understand theirs or their’s, several related distinctions become easier.
- Their vs theirs
- Your vs you’re
- Your vs yours
- Its vs it’s
- Whose vs who’s
- There vs their vs they’re
- Who vs whom
- Affect vs effect
- Then vs than
- Its vs its’
These pairs and groups are common sources of confusion because English often uses similar looking words for different grammatical functions.
Frequently Asked Questions
Is theirs or their’s correct?
Theirs is correct. Their’s is an incorrect spelling in standard English.
Why is their’s wrong?
Their’s is wrong because theirs is already the standard possessive pronoun. It does not need an apostrophe.
Is theirs a possessive pronoun?
Yes. Theirs is a possessive pronoun meaning belonging to them.
What is the difference between their and theirs?
Their normally comes before a noun, while theirs normally stands independently.
For example, “Their house is large” uses their, while “The house is theirs” uses theirs.
Can I write their’s in informal English?
You may see their’s in informal writing, but it is not the standard spelling. For correct English, use theirs.
Does theirs ever need an apostrophe?
No. The standard possessive pronoun is theirs, without an apostrophe.
Is the sentence “This book is theirs” correct?
Yes. “Theirs” correctly identifies the people who own the book.
Is “their’s” ever grammatically correct?
In standard modern English, their’s is not considered a correct possessive pronoun. Use theirs instead.
What is an easy way to remember theirs?
Remember that common possessive pronouns such as ours, yours, hers, and theirs do not use apostrophes.
Conclusion
When choosing between theirs or their’s, always choose theirs in standard English. The word is a possessive pronoun meaning that something belongs to them. It stands independently and does not need an apostrophe.
The easiest rule is simple: use their before a noun, as in “their house,” and use theirs when the possessive expression stands alone, as in “the house is theirs.” Do not write their’s.
Once this distinction becomes familiar, you can avoid one of the most common possessive spelling mistakes in English and write more accurately in academic, professional, and everyday contexts.
Philip Pullman is an American writer dedicated to creating clear and easy to follow English content. Through his work at LingRoya.com, he helps readers strengthen their language skills with practical and reliable guidance so that they can easily understand.
