Introduction to Relative Clauses: Turn Two Sentences into One with who, which, and that
You want to say "The man who called is my brother," but you end up only being able to split it into two short sentences: A man called. He is my brother. (There was a man who called. He is my brother.) It sounds like reading a list, lacking a bit of conversational flow.
Native speakers stick these two sentences into one: The man who called is my brother. (The person who called is my brother.) That middle part, who called, is today's main character, called a relative clause. Its job is very simple: to provide extra information about the noun before it, telling you "which one." Once you master it, your English will instantly upgrade from toddler-level to being able to express complete thoughts.
Don't worry, there is only one core action behind this sentence pattern. Once you learn it, you can take it with you.
What Relative Clauses Do
First, let's look at an everyday scenario. There are two books on the table, and you want to point out one of them:
- The book is mine. (This book is mine.) — The other person will ask: Which one?
- The book that I bought yesterday is mine. (The book I bought yesterday is mine.) — Now it's clear.
The inserted part that I bought yesterday narrows down the scope, letting the other person know "which book" you mean. This kind of clause that provides additional information and "would make the sentence unclear if removed" is called a defining relative clause.
Key takeaway: A relative clause always comes immediately after the noun it describes. When you see who, which, or that, look at the word right before it, and that is what it's describing.
First Trick: Find the noun being described first
To combine two sentences into one, the first step is always the same action: find the noun shared by both sentences.
Look at this pair of sentences:
- I have a friend. (I have a friend.)
- She speaks five languages. (She speaks five languages.)
What both sentences share is "that friend / she". Replace the she in the second sentence with a relative pronoun and connect it after friend:
I have a friend who speaks five languages. ✓ (I have a friend who speaks five languages.)
Let's break down the process:
- Find the shared noun: a friend = she
- This noun is a person, so use who
- Place who right after friend, followed by the rest of the sentence
As long as you start with the step "find the shared noun" every time, choosing the right word afterward will become very simple.
Second Trick: Use who for people, which for things, and that works for both
Which relative pronoun to choose depends simply on whether the shared noun is a "person" or a "thing".
who is used for people:
The teacher who helped me is very kind. ✓ (The teacher who helped me is very kind.)
which is used for things and animals:
This is the phone which takes great photos. ✓ (This is the phone which takes great photos.)
that can be used for both people and things, and is the most common in spoken English:
- The teacher that helped me is very kind. ✓ (The teacher that helped me is very kind.)
- This is the phone that takes great photos. ✓ (This is the phone that takes great photos.)
So when you get stuck, starting with that is almost always safe. Once you get used to it, you can gradually use who and which more precisely.
Be careful with a common mistake: don't translate Chinese "de" (的) directly into of, and don't stuff an extra pronoun in there.
- The man who lives next door is a doctor. ✓ (The man who lives next door is a doctor.)
The man who he lives next door is a doctor.✗
The relative pronoun who has already replaced he, so do not put he again after it. Remember: one of who, which, or that is enough—it serves as the subject itself.
Third Trick: Use where for places and whose for "whose"
In addition to people and things, there are two other useful words.
where is used for places, placed right after a noun that represents a place:
This is the café where we first met. ✓ (This is the café where we first met.)
Tip: If what you originally wanted to say was "in/at that place" (at the café / in the city), just use where and leave out the in or at.
whose expresses "someone's", used to connect a possessive relationship:
I know a girl whose father is a pilot. ✓ (I know a girl whose father is a pilot.)
Here, whose links to "the girl's father," which is equivalent to condensing her father into whose father. When you see "his/her/its" in Chinese and want to connect two sentences, think of whose.
Important Rule: Do Not Add Commas in Defining Clauses
This is the easiest trap for beginners to fall into. Just remember this simple rule of thumb: If removing this information makes the sentence incomplete, do not add a comma.
- People who exercise regularly sleep better. ✓ (People who exercise regularly sleep better.)
People, who exercise regularly, sleep better.✗
The point of the sentence above is specifically "the group of people who exercise regularly." who exercise regularly is essential information; if you set it off with commas, it becomes unclear who you are talking about, so no commas are added.
Tip for judging (The Removal Test): Cover up the entire relative clause and read the sentence again.
- If the meaning collapses or becomes too broad after covering it up → This is a defining clause → Do not add a comma
- If the meaning is still complete and that part is just extra information → That is another usage (with commas) that you can learn later
At this stage, most of the sentences you encounter to specify "which one" will belong to this comma-free type.
Three-Step Review
Next time you want to combine two sentences into one, follow this order:
- Find the noun shared by both sentences
- Choose the word: who for people, which for things, where for places, whose for possession; if you're not sure, just use that
- Connect it right after that noun, without repeating the pronoun or adding random commas
Let's practice. Combine these two sentences: I bought a jacket. + The jacket keeps me warm. The shared noun is jacket (a thing). The answer is I bought a jacket that keeps me warm. ✓ (I bought a jacket that keeps me warm.) Did you get it right? If you did, give yourself a pat on the back!
How to Practice in Loopy
To get fluent with relative clauses, you need to "encounter them repeatedly in real sentences." Loopy places sentence structures like who, which, and that into real-life conversations and listening scenarios in its graded courses. Moving step-by-step from A1 to B1 with gradually longer sentences, you will repeatedly see the "noun + relative clause" combination in natural contexts, slowly building your language intuition.
When you come across a relative pronoun you are unsure of, just tap the built-in dictionary to look up example sentences and see how native speakers use it. While practicing listening and shadowing, you will shadow complete long sentences like The man who called is my brother. Once your mouth gets used to it, you won't get stuck halfway through when speaking. The sentence patterns you have learned will also enter your forgetting curve review, appearing right when you are about to forget them to help you remember them firmly.
Not sure which level to start with? Take a placement test first, and let Loopy find the perfect starting point for you.