Knowing whether to use "in which," "of which," "at which," or any other mix of prepositions and relative pronouns can be a little confusing.
But don't worry; after reading this article, all will become clear!
In short, the choice of preposition and relative pronoun combination depends on the sentence's subject.
First, let's review a couple of grammar concepts to ensure you have the correct foundations before moving on to the question at hand.
If you feel confident about prepositions and relative pronouns, you can skip this section and jump straight to "Using prepositions with relative pronouns."
There are three different types of prepositions which are listed below with some examples:
Prepositions allow you to say where, when, or in which direction the noun is. Here are some examples of prepositions (underlined) used in a sentence.
My keys were under the pile of clothes.
I'll be waiting for you at the station.
It takes her 30mn to get from home to her office.
Relative pronouns allow you to refer to the noun in a sentence without the need to repeat the same word. They usually connect two clauses - a dependent or relative clause and an independent clause.
Here's a list of relative pronouns and when to use them:
To identify the appropriate relative pronoun for your sentence, you just need to look at the noun. Let's have a look at an example.
The dog that you adopted is so cute!
The relative pronoun "that" is the right choice to use here because the sentence is about an animal. "Dog" is the noun that "that" refers to.
Let's look at another example.
Is that the dog that you adopted?
Although the sentence is formulated slightly differently and is now a question, the subject is still an animal, so we use "that."
Of course, you could also use "which" since this pronoun is also appropriate for animals. Like in the following example:
Which dog did you adopt?
Now that's out of the way, let's move on to the question this article aims to answer: how to use a preposition with a relative pronoun correctly. Specifically, the pronoun "which." What if you want to use 'in Which,' 'of Which,' 'at Which,' etc.?
As you know, which can refer to a thing, animal, or place. Therefore, regardless of which preposition you use it with, it will always refer to one of those. It will never refer to a person.
So now you just have to choose a preposition to pair with "which."
Your choice of preposition will depend on what you're trying to say. Are you talking about a place, where something is, a point in time, or a location?
Let's look at a few preposition + relative pronoun combinations to understand how they work and study some examples.
The preposition "in" is used to talk about a location. You might say that you're "in the car" or your pencil is "in your pencil case." Therefore if you wanted to use "in which," it would be to talk about the location of a thing, animal, or place.
Let's imagine a conversation between you and your partner. You want to tell them that one of the kennels is leaking. You would say:
"One of the kennels is leaking. Could you take a look and see if you can fix it?"
To which your partner might say:
"Which kennel is it?"
And to this, you would answer:
"The kennel in which Rover usually sleeps."
In this case, the correct relative pronoun to use is "which" because that is the one your partner used in their question to you. But even if they hadn't, you would know that you should use "in" because Rover sleeps in the kennel. You also know to use "which" because that's the relative pronoun we use to talk about a thing when it's specific.
Let's use another example. Did you know "in" can also be a preposition of movement? That's right - you can talk going in a direction. For example:
"Which direction did he go in?"
"The direction in which he went is a secret!"
Let's repeat the same process with "on which." With "on" being a preposition of place, it makes sense that "on which" should be used in the context of referring to where a thing, animal, or place is.
Let's imagine that you wanted to report a broken chair in your office. You go to your boss and inform them that there's a broken chair. They ask you:
"Which chair is broken?"
To which you reply:
"The chair on which Sally's sitting."
Hopefully, it's becoming clearer now, and you're beginning to see the pattern. Let's have a look at another scenario, one that uses "at which."
"At" can be both a preposition of place or time. See how it carries two different meanings in the following sentences:
The movie starts at 10.30.
Julie's already at the party.
Therefore you could use "at which" to talk about where a thing, animal, or place is or when it is. Let's use the above examples, but we'll shift a few words around so we can use "at which." We get:
10.30 is the time at which the movie begins.
The party at which Julie is has started.
"Of" is quite a general preposition that doesn't really fit into one category. One of the ways it's used is to refer to possession. For example, you might talk about the bottom of your shoe:
My shoe, the bottom of which is soiled with dog poop, needs wiping as soon as possible!
We could carry on, but you get the picture. Apply the above to any preposition + relative pronoun combination.
Let's have a look at a few more examples:
If you look in the distance, you'll see a valley full of deer, behind which is a large house. That's where I live. ✅
This sentence is correct because the house is behind a valley, and a valley is a thing.
I was just in an hour-long meeting, during which I fell asleep.
This sentence is correct because you fell asleep during the party, and a meeting is a thing.
There's a forest through which you must walk before you get to the other side. ✅
This sentence is correct because you walk through a forest, and a forest is a thing.
Can you even see the light toward which they're asking you to walk? ✅
This sentence is correct because you walk toward something, and light is a thing.
This is the project to which I was referring. ✅
This sentence is correct because you refer to something, and a project is a thing.
Over there by the pool is my mum, next to which is my auntie. ❌
This sentence is incorrect because "which" can never refer to a person.
That's the day in which I'm having my birthday party. ❌
This sentence is incorrect because you have a party "on" a day, not "in" a day.
I've printed out a photo of the car to which I'm saving up money each month. ❌
This sentence is incorrect because you save up money "for" a car, not "to" a car.
My favorite vacation of all time was the trip under which I went last weekend. ❌
This sentence is incorrect because you go "on" a trip, not "under" a trip.
He's the person on which I'd give up everything. ❌
This sentence is incorrect because "which" can never refer to a person and because you give up something "for" a person, not "on" a person.
Though the sentence structure we've seen so far is the grammatically correct one, it isn't always the one that's most used in everyday conversational English. You're more likely to hear the preposition at the end of the sentence. Like this:
That's the car which I'm saving up for.
You might even notice that people scrap the "which" altogether and say:
That's the car I'm saving up for.
Note that although not technically correct, this form is acceptable in colloquial contexts. In more formal contexts like work emails, speeches, or academic papers, you'll definitely want to include both the preposition and "which" and use them together in the sentence.
Hopefully, you now feel more confident using "which" with a preposition. Remember that "which" always refers to a nonliving thing, animal, or place and that you must look at the subject in the sentence to choose the correct preposition.
If you'd like to become more confident with confusing English grammar concepts, head to our grammar blog, where we share tips and tools to help you progress.
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