Defining vs Non-Defining: Meaning Difference

Defining clauses are like a spotlight. They narrow down a group to one specific person or thing. Without them, the sentence doesn't make sense or changes its meaning entirely. If you say "The book is great," I might ask "Which book?" You reply, "The book that I bought yesterday." Now I know exactly which one you mean. Non-defining clauses are like a "P.S." at the end of a letter. They give extra info about something we already recognize. We use commas to set this extra info apart. It’s like putting the words in a little protective basket. If you remove a non-defining clause, the sentence still stands perfectly fine on its own. You are just being a bit more descriptive for your listener's sake.

1. 1Identify your main noun (the person or thing you are talking about).
2. 2Decide if the listener already knows exactly which one you mean.
3. 3If the info is essential to identify the noun, do not use commas (Defining).
4. 4If the info is just an extra detail, add a comma after the noun (Non-defining).
5. 5Choose your relative pronoun: who for people, which for things, that for both (Defining only).
6. 6For non-defining clauses, add a second comma if the sentence continues after the clause.
7. 7Remember: Never use that in a non-defining clause. It simply doesn't fit in the "comma basket."

Use defining clauses when you are ordering food and need to be specific. "I want the burger that has no onions." If you just said "I want the burger," the waiter wouldn't know which one. Use non-defining clauses when you are talking about unique things, like your mother or a specific city. "Paris, which is the capital of France, is beautiful." Everyone knows which Paris you mean, so the fact that it's the capital is just a nice bonus fact. In a job interview, you might say, "My previous manager, who is now at Google, recommended me." Since you only had one manager at that job, the info is non-defining. It makes you sound sophisticated and organized.

Do not use a non-defining clause if the information is actually required to understand the sentence. If you say, "People, who like pizza, are happy," you are saying *all* people like pizza and *all* people are happy. That's probably not true! You should use a defining clause: "People who like pizza are happy." This limits the "happiness" only to the pizza lovers. Also, avoid using that after a comma. It’s a major red flag for English teachers and grammar-savvy bosses. If you see a comma, reach for who or which instead.

The most common error is the "Missing Second Comma." If your extra information is in the middle of a sentence, it needs a "front door" and a "back door." For example: "My car, which is very old is still fast." This is wrong! You need that second comma: "My car, which is very old, is still fast." Another mistake is using that in non-defining clauses. "My brother, that lives in Spain, is a chef" sounds very unnatural. Use who instead. Finally, don't put commas in defining clauses. "The man, who stole my bag, ran away" implies there was only one man in the world at that moment. It's confusing for the reader!

You might confuse these with simple adjectives. "The red car" is similar to "The car that is red." However, relative clauses allow you to add much more complex information, like actions or relationships. "The car that I bought from my uncle" is much more specific than just "the old car." You can also compare these to appositives. Instead of saying "My friend, who is a doctor, lives here," you could say "My friend, a doctor, lives here." Both use commas because the information is extra. The relative clause just gives you a bit more "verb power" to explain things.