Decoding the Comma: When to Use It Before “Which” and “Who”

Using a comma before which and who can be tricky, but mastering this small punctuation detail improves clarity in writing. The difference lies in the type of clause you are dealing with: a non-restrictive clause adds extra information about a subject or someone, while a restrictive clause is essential to the core meaning of the sentence.

For example, in English, saying “My brother, who lives in New York, is visiting” uses a comma to clarify that the extra details about living in New York are supplementary; the main point is that the brother is visiting. In contrast, “The brother who lives in New York is visiting” omits the comma because the clause is necessary to identify which brother.

Knowing this distinction helps readers understand the structure, flow, and intent of your sentences, while reducing common mistakes that affect comprehension and stylistic choices.

Applying these rules consistently enhances your writing, whether in books, online, or academic contexts. Commas not only mark pauses but also define relationships between words, phrases, and relative pronouns like who and which, maintaining sentence integrity and coherence.

For example, “The car, which had a flat tire, was being fixed” versus “The car which had a flat tire was being fixed” demonstrates how misplacing commas can alter the meaning, confuse the reader, or change the intended emphasis.

Practicing these nuances through examples, exercises, and literary illustrations—from Jane Austen’s Pride and Prejudice to modern writing guides—helps writers develop awareness, accuracy, and precision in constructing sentences, ensuring effective communication and enhancing comprehension for any reader.

The ultimate goal is to master this fundamental element of grammar so your writing is both clear and stylistically elegant, whether describing a falcon diving 200 miles an hour, a delicious cappuccino in Paris, or a summer abroad adventure.

Understanding the Comma: A Simple Guide

The comma is one of the most confusing punctuation marks in English. Yet, it plays a critical role in making your sentences clear and easy to read. Knowing when to use a comma before “which” and “who” can save you from grammar mistakes that change the meaning of your sentence.

Think of the comma as a tiny pause in your speech. For example:

“My grandmother, who loves poetry, drinks tea every morning.” ✅
“People who drink coffee daily are often more alert.” ✅

The first sentence uses commas to provide extra information about the grandmother. The second sentence does not use commas because the information is essential to identify which people we are talking about.

In this guide, we’ll break down these rules with practical examples, real-life context, and exercises, so you can write confidently like a native speaker.

Restrictive vs. Non-Restrictive Clauses

To understand commas with “which” and “who,” we first need to know the difference between restrictive and non-restrictive clauses.

Restrictive clauses: Give essential information. No commas are used.
- Example: “The man who stole the violin was arrested.”
Non-restrictive clauses: Give extra, non-essential information. Commas are required.
- Example: “James, who is a millionaire, lives in Scarborough.”

Think of it like this: a restrictive clause narrows down which person or thing you mean, while a non-restrictive clause just adds more details, like a short story.

Tip: If you can remove the clause without changing the basic meaning, use commas.

Using Commas Before “Which”

The word “which” is almost always used in non-restrictive clauses, meaning it gives extra information. When “which” introduces such a clause, you should use a comma.

Correct: “The Ford Focus, which was made in the 1980s, is now a collector’s car.”
Incorrect: “The Ford Focus which was made in the 1980s is now a collector’s car.” ❌

Notice how the comma pauses the sentence and signals extra information. Without the comma, the sentence may imply there is more than one Ford Focus, which changes the meaning.

Practical Tip: Use commas before “which” whenever the clause can be removed without losing the sentence’s main point.

Using Commas Before “Who”

The rules for “who” are similar but slightly trickier.

Non-restrictive example (use comma): “William, who loves R&B music, moved to Boston.”
Restrictive example (no comma): “People who love R&B music often attend concerts.”

Key idea:

If the clause identifies “which person,” don’t use a comma.
If the clause adds extra, descriptive information, use a comma.

You can also think about it contextually: if your listener already knows who you are talking about, commas are likely needed.

Common Mistakes Learners Make

Many ESL learners struggle with commas because they translate rules from their native language. Some common mistakes include:

Adding a comma where it isn’t needed:
- Incorrect: “Students, who study hard, get good grades.” ❌
- Correct: “Students who study hard get good grades.” ✅
Forgetting a comma before a non-essential clause:
- Incorrect: “My grandmother who loves poetry drinks tea.” ❌
- Correct: “My grandmother, who loves poetry, drinks tea.” ✅

Other mistakes include confusing “which” and “that” or “who” and “whom.”

Remember: Commas are contextual. Always ask: Is this information essential or extra?

Real-Life Examples: Correct vs. Incorrect Usage

Sentence Type	Correct	Incorrect
Non-restrictive (extra info)	“James, who moved to the Isle of Man, enjoys falcon watching.”	“James who moved to the Isle of Man enjoys falcon watching.”
Restrictive (essential info)	“Cats who live in Boston have shorter life expectancy than Manx cats.”	“Cats, who live in Boston, have shorter life expectancy than Manx cats.”
Which in non-restrictive clause	“The Renaissance painting, which hangs in Belgium, is priceless.”	“The Renaissance painting which hangs in Belgium is priceless.”
Essential which (rare)	“Choose the coffee which you like best.”	“Choose the coffee, which you like best.” ❌

Notice how commas change the meaning entirely in some sentences.

Contextual Usage in Different Sentences

Understanding commas isn’t just about rules; it’s about context. Let’s explore a few real-life scenarios:

Business: “Ford’s policy, which was updated in the 90s, improved worker safety.”
History: “The monarch, who ruled in the 18th century, faced many conflicts.”
Romantic literature: “The hill, overlooking the town, inspired William’s poetry.”
Everyday life: “My grandmother, who drinks tea every Friday, bakes coffee-flavored cake.”

Even in casual writing, commas help convey nuance and tone.

Idioms, Expressions, and Related Phrases

Using commas properly can make idioms and expressions clear and readable. For example:

“A bird in the hand, which is worth two in the bush, teaches patience.” ✅
“Conveniently, the prom, which many students attended, was postponed.” ✅

Proverb tip: Think of commas as little markers of pause, just like in spoken language.

Practice Exercises for ESL Learners

Fill in the blanks with commas where necessary:

“The violin, ______ William bought last year, is a rare instrument.”
“Cats ______ live on the Isle of Man have a longer life expectancy than other cats.”
“My coffee, ______ I enjoy every morning, comes from Belgium.”
“James ______ is a millionaire, owns a spacious house on the hill.”
“The Ford Focus ______ was popular in the 1980s, is still loved in the US and UK.”

Answer Key:

who
who
which
who
which

Synonyms and Alternative Phrases Table

Word	Synonyms / Alternatives	Example
Which	That, whichever	“Choose the dress which/that fits best.”
Who	That person, the one who	“The baker, who/that won the award, lives in Scarborough.”
Comma	Punctuation mark, pause	“Use a comma before non-restrictive clauses.”
Extra info	Additional details, side note	“Non-restrictive clauses add extra info.”

Keyword Variations Comparison Table

Phrase	Use Case	Correct Example
Comma before which	Non-restrictive clauses	“The violin, which belonged to my grandmother, is priceless.”
Comma before who	Non-restrictive clauses	“William, who loves R&B, lives in Boston.”
Which vs That	Restrictive vs non-restrictive	“The coffee that I drink daily is strong.”
Who vs Whom	Subject vs object	“The man who called you is here.”

Fun Grammar Facts and Historical Context

The comma has been used since the Renaissance era to indicate pauses in reading aloud.
In the 19th century, grammar guides in the US and UK debated commas before “which.”
Famous authors like Scott and William sometimes ignored commas in their drafts, showing style can be flexible but contextual.

Grammar can even intersect with history and culture. For instance:

“A prisoner, who escaped from Boston prison in the 1980s, inspired many stories.”
“The Falcon, which soared over Europe, became a symbol in Romantic poetry.”

Quotes on Grammar and Language

“Grammar is the logic of speech, even more than the logic of thought.” – James D. Baker
“A misplaced comma can lead to a million-dollar misunderstanding.” ✅

Quotes like these remind us that punctuation is more than rules; it shapes meaning and style.

Applying the Rule in Writing and Speech

To naturally use commas with “which” and “who”:

Ask if the clause is essential or extra.
Use commas for non-essential clauses.
Read the sentence aloud; a natural pause often signals a comma.
Check context: writing for US vs UK readers may slightly vary.
Practice with worksheets, exercises, or Realtime editors like ProWritingAid.

Remember: Mastery comes from seeing rules in action in emails, essays, poems, and daily conversations.

FAQs

1. Do you always need a comma before “which”?
No. Use a comma before “which” only in non-restrictive clauses that give extra information. Essential clauses do not require a comma.

2. When should I use a comma before “who”?
Use a comma when “who” introduces non-essential information about a person. Skip the comma when the clause is essential to the subject.

3. Can commas change the meaning of a sentence?
Absolutely. “My grandmother who loves poetry drinks tea” vs “My grandmother, who loves poetry, drinks tea” have different meanings.

4. Are there exceptions in UK vs US English?
Yes. US English tends to use more commas before which, while UK English is slightly more flexible depending on style guides.

5. How can ESL learners practice this effectively?
Practice with worksheets, real-life examples, and reading. Also, listen for natural pauses when speaking English.

Conclusion

Using commas before “which” and “who” doesn’t have to be confusing. The key is to identify whether the clause is essential or extra. Non-restrictive clauses get commas, restrictive ones do not. With practice, context, and reading, you can confidently write sentences that are clear, natural, and grammatically correct.

Remember, commas are not just punctuation—they’re tools that guide your reader through your ideas smoothly, whether you’re writing about James, a falcon, a violin, or a hill overlooking Scarborough.

Aldous Huxley

Aldous Huxley was a visionary writer and philosopher whose works explored human nature, consciousness, and the future of society. His ideas continue to challenge minds and inspire generations.

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