Non-Defining Relative Clauses: Commas Required

These clauses provide additional information about a noun that is already clearly identified. Because the noun is already specific, the information in the clause is "non-essential." If you took a pair of scissors and cut the clause out, the sentence would still function perfectly. London, which is the capital of the UK, is very expensive. If you say London is very expensive, the meaning is still clear. The commas act as a signal to the reader. They say, "Hey, I am giving you some bonus info here!" It is a polite way to add detail without confusing the main message of your sentence. It keeps your writing organized and your reader informed without being overwhelming.

1. 1Start with your main idea. This is your "base" sentence. Example: My laptop is broken.
2. 2Pick the noun you want to describe. Let's pick My laptop.
3. 3Choose your relative pronoun carefully. For people, use who. For things, use which. For places, use where. For times, use when. For possession, use whose.
4. 4Create your extra information clause. Example: which I bought only last week.
5. 5Now, place this clause immediately after the noun it describes.
6. 6Insert your commas. If the clause is in the middle, use two. My laptop, which I bought only last week, is broken.
7. 7If the clause comes at the end of the sentence, you only need one comma before it. I finally fixed my laptop, which I bought only last week.
8. 8Remember: never use that in this specific pattern. It just does not fit the "extra info" vibe.

Use this when you want to add descriptive details in a professional way. In a job interview, you might say, My previous company, which was a small startup, taught me a lot about multitasking. It sounds much better than two short, choppy sentences. Use it when you are giving directions to someone. Turn left at the old oak tree, which has a birdhouse on it. It helps the listener identify landmarks more easily. It is also great for storytelling. It allows you to weave facts into your narrative without stopping the flow. Think of it as a way to multitask with your words. You are giving the main news and a side note at the same time. It makes you sound more fluent and natural, like a native speaker who is comfortable with complex ideas.

This is the tricky part. Do not use commas if the information is necessary to know *which* thing you are talking about. If I have three brothers and I say, My brother who lives in New York is a doctor, I do not use commas. Why? Because the phrase who lives in New York tells you *which* brother I mean. If I used commas, it would imply I only have one brother, and "living in New York" is just an extra fact. Also, avoid using these clauses if your sentence is already getting too long. Too many commas can make a sentence feel like a bumpy road. If you have three or four clauses, just start a new sentence. Your reader will thank you for the breathing room!

The "Missing Second Comma" is the king of errors. People often remember the first comma but forget to "close the gate." The movie, which was three hours long was boring. That missing comma after long makes the sentence feel unfinished. It is like wearing only one shoe. Another big one is the "That" mistake. In defining clauses, that is fine. In non-defining clauses, that is forbidden. My car, that is blue, is fast. (No!). Use which. Lastly, watch out for pronoun confusion. Do not use who for things or which for people. Your car is not a person, and your teacher is not an object! Even native speakers mess this up sometimes, but you can be better than that.

Let's look at Defining vs. Non-Defining. Defining: The students who studied passed the test. (Only the ones who studied passed). Non-defining: The students, who studied hard, passed the test. (All the students passed, and by the way, they all studied hard). It is a small change in punctuation, but a huge change in meaning. It is the difference between a specific group and a general statement. One is a filter; the other is a highlighter. Defining clauses narrow down the subject. Non-defining clauses just add a little light to it. Think of it like a grammar traffic light: the commas tell the reader to slow down and enjoy the extra detail.