What or Which: Differences and Usage

Who, what, when, where, and why — these words are staples of the English language. It may be simple enough to say, “Do what sounds right,” but often, it doesn’t work that way.

The words “what” and “which” are both question words as well as interrogative pronouns, and we can often use them interchangeably. But while this can be the case in many instances, the meaning of each differs in certain contexts. The word “which” can only provide limited answers, while the word “what” offers almost unlimited options.

Despite the appearance of “which” and “what” as synonyms, there is a need for caution in your writing. Continue reading to learn to manage this dilemma the significance of “which” and “what” as both determiners and pronouns.

Interrogative Words

“Which” and “what” are both common interrogative words, also known as question words or “wh”-words (source).

English derives the word “interrogative” from the Latin word interrogo; the first part, inter, means “between/among,” and rogo means “ask” (source).

This means that when you put “interrogative” in front of any word, the concept relates to questioning. We will break down interrogative words and their offshoots throughout this article.

If you’re a first-language English speaker, chances are you’re well-acquainted with interrogative words in your day-to-day interactions. The words in this category are:

Who/Whom	What
When	Where
How	Which
Why	Whose

You can use all of these words to ask questions that will allow you, the speaker, to receive information from whomever you’re talking to.

Although, contrary to what a “question word” means, these words exist and have their place outside of questions as well, typically in the form of pronouns or indirect questions.

This may sound somewhat complicated, but you’ll find question words and their purposes are quite familiar when writing your own sentences.

Example Table

There is a brief description of each question word in the table below.

Question Word	Requested Information/ Information Referred to	Example/s
Who	A person/people	Who did that?She will never forget who was to blame for her plight.
When	A time	When does the party begin?He asked when I would be ready.
Where	A location	Where is your new house?She didn’t know where to look first.
Whose	To whom something belongs	Whose bag is this?He asked whose fault it was, so I kept quiet.
How:	The manner	How are we going to do that? I forgot how I fixed it last time.
How	To what extent or what amount	How far have you gotten in the book? How close are you to finishing the project? I don’t know how tall he is.
How	Others’ emotional/physical states or thoughts	How is your uncle? My boss asked me how I was feeling today.
How	To emphasize	How kind of you to offer your assistance.“How terrible!” she remarked sarcastically.
Why	A reason or explanation	Why do the leaves change color in the fall? I don’t know why she did it.

The only two words left that, sadly, are not quite as straightforward are “which” and “what.”

Which Versus What

We use both “which” and “what” to ask for information, but they’re different as they do not have the limitations of most of the previous question words (source). 

The words “which” and “what” can help us to get answers that refer to times, places, people, and things.

• What time are you going to arrive? (expected answer: a time)
• Which neighborhood do you live in? (expected answer: a place)
• What is her name? (expected answer: a person/name)
• Which theme-park ride is your favorite? (expected answer: a thing/object)

The only difference is the word “which” asks for a specific answer with a limited number of options available, while the word “what” has a more unlimited selection from which to choose.  

What as an Interjection

“What” also has another informal purpose entirely separate from “which.” It is similar to an interjection. You can use “what” to indicate strong emotions, including surprise and anger (rhetorically), or for asking a person to repeat or explain themselves.

Speaker A: Did you know tomatoes are a fruit?
Speaker B: What?! (surprise)

Speaker A: Mitosis is the process of cell division.
Speaker B: Sorry, what? (asking for clarification)

This is the one situation where you are unlikely to ever confuse the words “which” and “what.”

Which and What in Agreement

It is often correct to use either word. For example:

• Which train are you taking?
• What train are you taking?

These sentences have the same meaning. The only difference is that the speaker from the first example likely thinks of fewer trains than that of the second.

So, if while writing you’re aware that an answer is open or has a lot of options, use “what.” If you believe the number of answers is limited, use “which.”

Which and What in Discord

However, there are moments where you can only use either “which” or “what,” but not both interchangeably. For example:

• What is your name?
• What is your phone number?

Here, you will use the word “what” because there is an infinite number of names a person can have, and the same is true for available phone numbers.

The only way you could replace “what” in these sentences with “which” is by asking this question with a list of names or a variety of spellings, or perhaps a limited list of potential phone numbers. You can see this in examples such as:

• Which is the correct spelling of your name: Stacey or Stacy?
• Which is your correct phone number, 123-456-7890 or 123-456-7891?

Let’s try another example. Imagine you are reading a book from a popular trilogy when you run into a fellow reader. Which response makes more sense?

• “I love that series! What one is your favorite?”

Or

• “I love that series! Which one is your favorite?”

If you answered the second option (which), you are correct. That is because your answers to this question are limited to either the first book, the second book, or the third book.

If someone asked you, “What book is your favorite?,” the question is more general. Therefore, the assumption is that you can speak of any book in existence, rather than limiting yourself to responding about a single book series.

Understanding the Role of Determiners

Determiners are words that you’ll find before a noun or a noun phrase, and they provide clarity to the noun. They can show whether the noun is specific or general (source). 

Determiners have two purposes: 

1. Referring
2. Quantifying (numbering)

Definite article	the
Indefinite articles	a/an
Pronouns and Possessives	Your, his, her, its, my, their, our, (possessive)’s, etc.
Demonstratives	That, this, those, etc.
Quantifiers	Few, fewer, many, most, some, any, etc.
Numbers	One, five, a hundred, etc.
Difference words	Other, another, etc.
Distributives	All, neither, either, every, etc.
Interrogative	Which, what, whose, etc.

Determiners can be at various points in a sentence, as long as they’re before a noun. You can see this in the sentences below — you’ll see that we’ve underlined the determiners:

• Your house is really large.
• “You can’t eat that sweet!” she complained.
• If I’ve told you once, I’ve told you a thousand times.

The Word “What” as a Determiner

“What” is a general determiner (source). This means that when you use “what” in a sentence as a determiner, it doesn’t refer to a specific noun.

• What apartment do you live in?
• I do not know what food she likes.

The Word “Which” as a Determiner

“Which” is a specific determiner. So, when you use “which” as a determiner, the noun refers to a limited selection.

• She has already released nine albums. Which one is your favorite?
• I can’t recall which website I read it on.
• Which teacher is your favorite — Ms. Smith or Mr. John?

Understanding the Role of Pronouns

Pronouns are words that you can use in place of nouns and noun phrases. This is because when writing or speaking, repeating the noun can lead to strange and repetitive sentences. For example:

• The girl read the book, and the girl found the girl really liked the book.

The sentence sounds awkward and stilted. Pronouns can help you fix this issue, and there are multiple ways to make this sentence sound better, including:

• The girl read the book, and she found she really liked it.

Or 

• The girl read the book, which she found she really liked.

Identify the Pronouns

In these examples, you’ll see that we’ve underlined the pronouns. There are also two types of pronouns used. Look at the table below, and see if you can identify which pronouns we used above. The answers will follow below the table (source).

Type of Pronoun	Explanation and Examples
Personal Pronouns	Words that stand in place of people or things, such as he, she, they, I, me, you, it, they, etc.
Reflexive Pronouns	Words ending in -self or -selves, like myself, yourself, themselves, etc.
Indefinite Pronouns	Words that end in -thing, -body, -one or -where (typically one word, with the exception of no one). Common examples include someone, anybody, and everywhere.
Possessive Pronouns	Possessive pronouns refer to ownership, such as the words my, mine, yours, ours, theirs, etc.
Interrogative Pronouns	Once again, the word “interrogative” refers to asking questions. The relevant pronouns are the wh-words, including which, who, what, etc., when we use them to ask questions.
Relative Pronouns	We use relative pronouns to link one phrase/clause to another. Examples include who, whom, that, which, and their -ever counterparts (whomever, whichever, etc.).
Indefinite Pronouns	Indefinite pronouns are general pronouns that stand in place of nouns. The words end with -body, -one, -thing, and -where (such as somebody, nowhere, and everything).
Demonstrative Pronouns	We use demonstrative pronouns to refer to a noun or pronoun. Examples include this, that, and those.

The answers are as follows:

• She and it are both personal pronouns.
• Which is a relative pronoun.

You likely noticed “which” fell under both relative and interrogative pronouns, and that may seem confusing. However, it is fairly easy to differentiate the type of pronoun “which” is, depending on the context.

The Word “Which” as a Pronoun

When we use it in a question, “which” is an interrogative pronoun, meaning it follows the same rules as interrogative words. So, you should use it when you’re asking a question that has a restricted/limited range of answers.

For example:

• Which animal would you like to get?
• Which team do you think will win this season?

“Which” is also a relative pronoun. It stands between two clauses/phrases. When “which” is a relative pronoun, it usually stands in place of animals or things.

Look at the sentences below. Instead of repeating the words in bold, we can use “which” instead.

• She had a sort of attitude which made others scared out of their wits.
• I boarded the plane, which was taking me to Canada.

The Word “What” as a Pronoun

In standard English, “what,” unlike “which,” is never a relative pronoun. However, there are still two positions it can hold as a pronoun.

First, it can be at the start of a sentence as an interrogative pronoun:

• What did you think of the latest episode?
• What happened on your birthday?

Second, the word “what” can also stand in place of “the thing(s) that” at any point in a sentence:

• I’ll never forget what you said to me.
• My dad told me I could do what I wanted.

So, if you’re writing a sentence where you feel you could use “what” in the middle as a pronoun, attempt to replace the word with “the thing(s) that.” If it doesn’t make sense, go for “which/who” or “that” instead.

If you do want to read more about using “that” in a sentence, look at the article “In Spite or Inspite: Which is Correct?”

Final Thoughts

“What” and “which” are both words that have their place in the English language. In a lot of situations, knowing which one to use is easy. 

At other moments, however, you have to consider what you are referring to while writing, or where the word is positioned in the sentence, to decide which is the correct word to use.

With time and practice, this will soon become second nature. Be sure to talk, write, ask questions, and put your skills to the test!