Get the grammar rules for using that and which.
There’s a lot of confusion about that and which. These two words are often used interchangeably, even though they’re not necessarily interchangeable.
Historically, that and which may have carried the same meaning, and some English dialects may allow for that and which to be swapped without affecting the meaning of a sentence.
However, in American English, the grammar rules offer a distinct difference between the two words. By the time you’re done reading this post, you’ll fully understand the difference between that and which, and you’ll be able to use both words correctly.
That and Which
As with most grammar rules, there are exceptions and exemptions from the standard ways that and which should be used in a sentence. To gain understanding of confusing word pairs, it’s always best to start with the basics. As we look at how to properly use that and which, we’ll focus on simple, standard usage.
That and which can be categorized into several different parts of speech. Both words can function as adjectives and pronouns. Additionally, that can serve as a conjunction and as an adverb. Today, we’re looking at how that and which should be used when they are working as relative pronouns.
Relative Pronouns
From Wikipedia: “A relative pronoun is a pronoun that marks a relative clause within a larger sentence. It is called a relative pronoun because it relates to the word that it modifies.”
Like adjectives and adverbs, relative pronouns modify other words. Adjectives modify nouns:
- I have a car.
- I have a red car.
Adverbs modify verbs:
- I am walking.
- I am walking quickly.
The main difference between adjectives and adverbs is that adjectives usually modify things (nouns) while adverbs modify actions (verbs). Relative pronouns also modify words, but they often do so as clauses rather than as single, descriptive words. In the examples below, the clauses are italicized.
- Bring me the bucket.
- Bring me the bucket that has apples in it.
- The bucket, which has apples in it, is blue.
The difference between the words that and which and how they are used as relative pronouns depends on whether the clause they belong to is restrictive or nonrestrictive.
Restrictive and Nonrestrictive Clauses
Restrictive Clauses Are Necessary
A restrictive clause is necessary to the meaning of a sentence. For example:
- I want the bucket that has apples in it.
If you removed the clause “that has apples in it,” the meaning of the sentence would be lost. Nobody would know which bucket the speaker wants. The clause is necessary to the meaning of the sentence and is therefore a restrictive clause. Because it’s a restrictive clause, it should take the relative pronoun that.
Nonrestrictive Clauses are Unnecessary
A nonrestrictive clause is not necessary to the meaning of a sentence. In fact, it can be removed from a sentence without affecting its meaning. For example:
- The bucket, which is blue, has apples in it.
- There are apples in the bucket, which is blue.
If you removed the nonrestrictive clause “which is blue,” from either of the sentences above, the meaning of the sentences would not be lost. We’d still know that the bucket has apples in it. Note that in the second example, the nonrestrictive clause adds information about something that has already been identified. Because the clause is unnecessary to the meaning of the sentence, we know it’s a nonrestrictive clause, and therefore should take the relative pronoun which.
- Use that before a restrictive (necessary) clause.
- Use which before a nonrestrictive (unnecessary) clause.
The Easy Way to Remember the Difference Between That and Which
I Needed That
If you need the clause to maintain a sentence’s meaning, then use that. A quick trick for remembering this grammar rule is the phrase “I needed that.”
Which?
Because which is also an interrogative pronoun used to mark questions, it is questionable. You can take it or leave it. It’s not necessary. Think of the word which with a question mark (which?) to remind yourself that if the clause’s presence is questionable and can be removed, then you should use the word which to introduce the clause.
Exceptions and Notes
Here are some exceptions and notes to these rules:
- Which can be used restrictively when it’s preceded by a preposition. For example, “The bucket in which the apples have been stored is blue.”
- Which is almost always preceded by a comma, parenthesis, or a dash.
- In British English, there is little distinction between that and which.
Has this article helped clarify any questions you’ve had about grammar rules? Do you have any other questions about that and which? Do you have any tips to share for remembering how to use these two words? Leave a comment.
Sources (aff links):
- The Chicago Manual of Style
- Grammar Girl, “Which Versus That“
- Wikipedia, “Relative Pronouns“
Recent Examples on the Web
The real Morel and Wilson had no luck reaching MTA, which shut down 20 years ago and was dropped from the Colorado secretary of state’s registry in 2001.
—
Grace Schneider, The Courier-Journal, 6 July 2017
June Gloom is over, summer is officially here – and the days are only getting shorter – which is reason enough to knock off work early and head to happy hour.
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Reeder’s dog is allergic to wheat, which is not uncommon.
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—Jim Varsallone, miamiherald, 6 July 2017
This year’s show will be at the LaPorte County Fairgrounds, 2581 W. State Road 2, LaPorte, which can accommodate 90-100 vendors.
—Post-Tribune, 5 July 2017
Many progressives object to developers’ business model, which depends on building new units and charging as much as possible for them, even if that makes them unaffordable for longtime residents.
—Alana Semuels, The Atlantic, 5 July 2017
Residents seem to be embracing the electric people-movers, which are now operating under summer hours of 11 a.m. to 11 p.m., Hamik said.
—Erin Hegarty, Naperville Sun, 5 July 2017
The biggest spending cuts hit the Medicaid program, which provides health coverage for low-income children and adults, including paying for nearly half of all births and much of the cost of nursing home care.
—Julie Appleby, Kaiser Health News, 5 July 2017
See More
These examples are programmatically compiled from various online sources to illustrate current usage of the word ‘which.’ Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.
OP should have noted from «They have the Supreme Court on their side[,] which ruled in their favour» (in the linked question) that «which» can often apply to the entire preceding phrase.
OP’s first example here is both clumsy phrasing and conceptually flawed. Per the above, the natural interpretation is the fact that Class Sheltie of Dog.scala illustrates variable shadowing is the reason the class does what it does. That can only make sense if we interpret it as meaning the class is specifically written for the purpose of illustrating variable shadowing.
But OP says the reason the class does what it does is because of variable shadowing, which I don’t think that makes any sense at all. I’m stuck between a weird interpretation and a nonsense one.
The second example is natural English, and unambiguous. Although only the default constructor is referenced by which, not the whole of the preceding phrase, that’s not a problem. It’s the only plausible noun phrase, and we can easily see it’s a suitable candidate for being the body of the class. It could be recast to put «which» closer to its referent, but that might seem a little more awkward…
This causes the default constructor, which happens to be the body of the class itself, to be invoked.
Note that if instead OP’s second example had been…
This causes the default constructor to be invoked, which is undesirable.
…we’re back with the «whole phrase» interpretation — it’s not the default constructor which is undesirable, but the fact that something causes it to be invoked.
The interrogative pronouns and determiners “what” and “which” are fairly similar when we use them in a sentence. They come at the same point in the sentence, but that doesn’t mean they’re used for the same reason. Let’s see when to use which one over the other!
When Should I Use “What” Vs. “Which”?
“What” should be used when referring to unlimited choices that someone can make (i.e., “what do you want to eat”). “Which” should be used when referring to a more specific number of options (i.e., “Which person in your family are you closest to”).
If we’re presented with an infinite number or an undetermined number, then “what” is always the choice. However, if the choices are narrowed down to a more specific selection, we can use “which.”
It’s worth noting that “what” can be used in place of “which” it’s just more informal if you were to do so. However, you can’t use “which” in place of “what” all the time because “which” only works when a numbered selection is asked for.
7 Examples Of How To Use “What” To Ask A Question
If you do not entirely understand the reasoning for the words and meanings yet, don’t worry. We’ll run you through some examples of how both of the pronouns are used so you can start trying them out yourself and understanding how they work.
“What” is used when there are unlimited choices to make with a decision. It’s also the more informal choice of the two and can be used interchangeably with “which” if necessary (mostly in speaking).
- What do you want to eat tonight?
- What school do you go to?
- What is your name?
- What was the last thing you said to her?
- What happened to you?
- What is in the box?
- What can I do to help you?
The examples here so that “what” is more of a general question. We use it when we don’t know the specific choices that are listed.
To dive deeper into that meaning, look at example 3. “What is your name” is a general question because there are endless names in English that people can have. We’re keeping the question general but only looking for one answer; that’s why “what” is used.
Incidentally, we can use “which is your name” if we’re already presented with a list of names (imagine if you have a list of names of people in a classroom). If you ask one person which of those names applies to them, that’s when “which” would work.
Generally, with more open-ended questions, “what” is the correct choice.
7 Examples Of How To Use “Which” To Ask A Question
Now let’s look at the more specific pronoun or determiner, “which.” We can use this in a few ways, but it’s mostly to determine the answer to something when we have a specific number.
“Which” is used when we have a limited number of choices. We may already be presented with a list of potential answers, and we’re just asking someone to clarify which one applies to them.
- Which house is yours?
- Which one is yours?
- Which of these looks best to you?
- Which artwork do you want to take home?
- Which dates are you away in June?
- Which car is yours?
- Which is the best address for you?
In each of these examples, we use “which” when we already have a list of things and are determining which one applies to whoever we’re speaking to.
To elaborate, if you look at example 1, you’ll see us asking, “which house is yours.” The implication is that we’re already on a street that someone has told us they live. Now we’re asking which house on the street they live at so we can walk them to it.
The idea is that we always have knowledge of a few potential answers. Generally, things don’t have to be as specific as a simple A, B, or C answer.
Sometimes, more general questions like “which country are you from” work too, because we’re asking them “which country” they belong to from the list of known countries in the world. Since this is a quantifiable value, we use “which” to ask for the answer.
What Part Of Speech Are “What” And “Which”?
Both “what” and “which” are used in the same part of speech when we use them. They both start as a question, and we use them to determine an answer to that question from the person we’re speaking to.
“What” and “which” are known as interrogative pronouns and are also considered interrogative determiners if you take it a step further.
Interrogative Pronouns
First, let’s talk about what an interrogative pronoun is.
You may be familiar with some of the interrogative pronouns in English like “what,” “which,” “who,” “where,” and “when.” All of these pronouns are used to ask a question (or an “interrogative” statement).
Whenever we use them in this sense, we put them at the start of the sentence, and they act as the pronoun of the sentence.
- What are you doing?
- Which is the best for you?
- What do you want?
- Which of these are you?
As you can see from these examples, an interrogative pronoun is always followed by either a preposition or a verb to continue the question structure. We use “what” and “which” in the same way to find out more about this.
Interrogative Determiner
We can take the two words one step further and group them into a more specific list of interrogative words.
Interrogative determiners are used to determine a noun or object in a sentence. “What,” “which,” and “whose” are good examples of this. We immediately follow the determiner with a noun (which it modifies in the sentence).
All determiners in English come before a noun, and they’re designed to determine the meaning of the noun for that specific sentence. Let’s look at a few examples.
- What country are you from? (noun = country)
- Which house is yours? (noun = house)
- What food do you want to eat? (noun = food)
- Which school do you go to around here? (noun = school)
As you can see, we immediately follow the interrogative determiners with a noun to make them work. If we don’t use a noun, we are instead using them as a simple interrogative pronoun to ask a question.
Can “Which” And “What” Ever Be Used Interchangeably?
We’ve briefly touched on using the words interchangeably previously, but let’s elaborate more.
“Which” is the more formal choice of the two, but “what” can replace it in informal situations when asking about a specific list of answers. However, “what” can’t be substituted with “which” when we’re asking for a general answer.
Let’s look at some examples to explain:
- Which one is yours?
- What one is yours?
In these examples, we have a list of potential answers present. That means the correct pronoun is “which” in this instance. However, “what” also works in a more informal sense, and you can use them interchangeably.
Now, let’s look at a more general example:
- What is your name?
- Which is your name?
The first example works well when you’re determining their name without knowing anything else. However, “which is your name” is incorrect unless we already have a list of names in front of us. That’s why you can only use them interchangeably in the more specific sense.
How Using “Which” Vs. “What” Can Change The Meaning Of The Sentence
We’ve covered all the major differences between the two words, so now let’s go over how the sentence’s meaning can change based on which one you choose to use.
- What town are you from?
- Which town are you from?
We use the first example when we’re trying to figure out where someone lives. We may have no idea where they come from and are trying to figure it out.
The second example is more specific, meaning we have a rough idea of which part of the country they’re from. We’ve narrowed down the list of towns, and now we’re just asking them to clarify.
- What do you want to eat?
- Which do you want to eat?
The first example is a general question usually asked before starting to cook or visiting a restaurant. It’s asked to determine what someone fancies to eat on the day.
The second example is a specific question we use when we’re already presented with food options. For example, if a food trolley has been wheeled out, you might be asked: “which” of the plates in front of you look the most appetizing.
What Are The Similarities Between Which And What?
“Which” and “what” aren’t completely different from each other. We’ve already shown you the major differences, but they come with similarities, too.
| Which | What |
| Interrogative Pronoun | Interrogative Pronoun |
| Starts a question | Starts a question |
| Determines a noun | Determines a noun |
| Can be general | Is general |
These are the main similarities between the two words. You can always use “what” in place of “which” in a sentence, showing that they link very closely.
What Are The Differences Between Which And What?
Now let’s go over a few differences between the two pronouns.
| Which | What |
| Specific | General |
| Needs a predetermined list | Works with unlimited answers |
As you can see, the major difference between the two is that “what” works in a general sense, while “which” only works in a specific sense. You can’t use “which” in a general way, which makes it incorrect to use interchangeably with “what.”
When Should You Use “Which” Vs. “That”?
Generally, we use “which” as an interrogative pronoun, which means it’s how we start a question to interrogate someone and find out an answer.
We use “that” when we are answering questions that start with “which.” “Which,” asks for a specific answer from a list of things, while “that” answers the question by pointing out which specific thing applies.
For example:
- Which of these works best for you?
- That one works best for me.
As you can see, we use “that” to reply to someone asking us “which” thing works for us.
16 Common Confusions About “What” Vs. “Which”
“What” and “which” should hopefully be quite clear by now. However, people have a few common misconceptions about the uses of the two, and we wanted to clarify the following specific examples!
Which Day Or What Day?
“Which day” should be used when you’re determining the day from a specific list (i.e., the number of days in a month). “What day” should be used when you’re asking for a general day without any idea of when something might occur.
Which City Or What City?
“Which city” should be used when you already know someone’s rough location, and you’re trying to narrow down where they’re from. “What city” should be used when you have no idea where someone is from and want to learn more about them.
Which Color Or What Color?
“Which color” should be used when you’ve presented someone with a collection of colors and want to ask them which one they like best. “What color” should be used when you’re more general without knowing an exact answer (like asking for someone’s favorite color).
Which Extent Or What Extent?
“Which extent” should be used when you already know a list of a few choices you can make that will be an extent (“to which extent will you help”). “What extent” is used when the choices are unlimited, and you’re not sure what to do yet.
Which Song Or What Song?
“Which song” should be used when you’re asking for someone to pick a song from a determined list (like a playlist). “What song” should be used when generally asking for a song choice without a preconceived idea of the answer (like a favorite song).
Which Language Or What Language?
“Which language” should be used when you’re asking someone which language they speak from a list of languages that you’re familiar with. “What language” should be used when asking for a general language if you’re unsure what they might be able to speak.
Which Activities Or What Activities?
“Which activities” should be used when asking about what things people do (usually a club will have a list of activities, and “which” is used to determine the exact one). “What activities should be used when you’re unsure of the specific answer and the list of activities is unlimited.
Which Floor Or What Floor?
“Which floor” should be used when you have a selection of floor choices in front of you, and you want to pick the best one for what you need. “What floor” should be used when you’re asking a general question about ideas that people might have about their flooring.
Which Country Or What Country?
“Which country” should be used all the time as it’s generally a specific question. We already have a full list of countries in the world, and we’re picking a country from that specifically. “What country” should be used to ask the same question in an informal way.
Which Kind Or What Kind?
“Which kind” should be asked when you’re asking for a specific kind from a list of potential options (“which kind of art appeals most to you here?”). “What kind” should be used when asking for a general answer to a question about preferences.
What Year Or Which Year?
“What year” should be used when trying to determine when an event happened without knowing much about its context. “Which year” should be used when you have an idea of when something happened but want to clarify the exact year based on a few examples.
What Way Or Which Way?
“What way” should be used when asking for a general direction to a destination. Usually, we haven’t already seen the paths to get there. “Which way” should be used when we’re already heading to a destination and asking for a more specific path at a certain point.
What Information Or Which Information?
“What information” should be used when trying to find out some information without knowing much about the source of it or why it’s necessary. “Which information” should be used when you have a list of information in front of you, and you’re trying to determine which is the best one.
What Dates Or Which Dates?
“What dates” should be used when you don’t have the exact month listed of when someone might be doing something (“what dates are you leaving?”) “Which dates” should be used when you can narrow it down to a month or season (“which dates in June are you away?”)
What Car Or Which Car?
“What car” should be used when asking for a general preference of what car someone might like or what car they drive. “Which car” should be used when asking for a specific idea of what car belongs to someone (“which car is yours in this parking lot?”)
What Time Or Which Time?
“What time” should be used when asking for a time without any real idea of what point of the day it is (“what time is it?”) “Which time” should be used when you want to clarify a meeting time that you should already know (“which time are we meeting?”)
Martin holds a Master’s degree in Finance and International Business. He has six years of experience in professional communication with clients, executives, and colleagues. Furthermore, he has teaching experience from Aarhus University. Martin has been featured as an expert in communication and teaching on Forbes and Shopify. Read more about Martin here.
Just like a lot of words in the English language, this word has a double purpose. It can either be used as an adjective or as a pronoun.
- Adjective
This word is considered as an adjective when it is used to modify a noun. It can either indicate what particular one or it can also mean “whichever.” For example, in the sentence below:
I’m still deciding on which coat should I wear.
The word “which” is an adjective that modifies the noun “coat,” and is thus considered as an adjective.
Definition:
a. what one or ones of a group
- Example:
- She kept an organized record of which employees took their vacations.
b. whichever
- Example:
Turn it which way you like.
2. Pronoun
This word can also act as a pronoun when it is used to refer to something that has already been mentioned. It is commonly used at the beginning of the clause that provides further details about the noun. In the example below:
The crocodile which weighs over 2000 pounds was captured.
The word “which” is a pronoun that refers to the mentioned noun “crocodile.”
Definition:
a. used referring to something previously mentioned when introducing a clause giving further information
- Example:
- The computer which keeps breaking down was finally replaced with a new one.