Which floor do you live on?

I heard people say “which floor do you live on?” , is it okay to say “what floor do you live on?”
I don’t really know when to use “what” and “which”.
And the other sentence is “what grade are you in?”
You don’t say “which grade are you in?” right?

Thank you!!

All the ways of asking a question that you have mentioned can be heard in everyday English, and would clearly be understood…

On a similar but more tricky note, however, you may like to consider the following two statements:

  • Toys that are dangerous should never be given to children.

  • Toys which are dangerous should never be given to children.

Do you see a difference?

No, I think they are the same.

I also think the toys sentences are the same.

Lily, in terms of your question about what and which, I think all the examples you used were interchangeable. To be more specific, “which” may be more technically “correct” if there is such a thing in this case, or at least i tends to be used when you are referring to items that are in a defined set or sequence.

So, the floors in a building: which one do you live on?

Of all the presidents of the United States, which one was best? Washington, Lincoln, Reagan? (You could say “who was best” also, but “what one” would be awkward)
Between China and Taiwan, which place has a higher population? (saying “What place” would be awkward.)

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In your first example, you will probably hear both “which” and “what” floor do you live on? “Which” is more accurate in contexts where the speaker is asking the other person to identify the exact floor – e.g., it is the third, fourth or tenth floor? Asking the question, “which floor do you live on,” requires a specific answer. “I live on the sixth floor.”
Similarly, “which color shirt do you like?” “I like the blue one.”
(If the question is asked, “what color shirt do you like,” this is more likely a question about what color shirt you like in general and is not in reference to distinguishing between two or more shirts of different colors.)
“Which day is best for you?” “Thursday works best.”

You will hear some people say, “what floor…what color… what day…” but they are more informal/less specific ways of asking. If you want a specific answer, phrase the question more specifically by using, “which.”

“What” in a question is often used more generally.
“What do you like to drink with dinner?” (This is asking about drinks in a general way, i.e, what kind of drinks.) One could answer generally, “I like wine.” “I prefer water.” One could also be a bit more specific, "I like red wine.“I like seltzer water.” However, it would be somewhat odd to answer too specifically, “I want to drink the cabernet sauvignon 2003,” unless several types of red wine were already discussed. That is, how the question is phrased affects the amount of detail in the answer.

Generally one doesn’t give a very specific answer unless the question asks for such detail by using “which.” “Which wine do you want to drink with the appetizer?” “I prefer the white burgundy.” “Which table do you prefer, by the window or on the terrace?” “I prefer by the window.”

Regarding “grade” (class level), one would commonly ask in a general way, “what grade are you in” if you don’t know much about the person. However, you would say as a follow-up question, “in which grade did you start learning a foreign language?” “Which subject was your favorite?”

Thus, while in informal speech some people use both “which” and “what” in questions, there are subtle differences in the kind of information they are requesting. Context is important. A more general question tends to begin with “what” yet a more specific question tends to begin with “which.”

Regarding Carrington’s post with respect to “which” and “that” in clauses,
this is more complicated. The difference between the use of “which” and “that” concerns whether the clause that each introduces is “restrictive” – i.e., essential – or not (“unrestrictive”) with respect to the meaning of the sentence. Most native speakers who do not write professionally are probably unaware of the rule which undoubtedly explains why you are likely to hear both words used more or less interchangeably in informal speech. However, that native speakers make grammar mistakes doesn’t mean that you shouldn’t learn the rule. While some English grammar rules can sound awkward in informal speech, correctly using the rule for “that” and “which” will not make you sound awkward or overly formal.
Google “when to use that and which” for many explanations of this rule. (Hint: “___are dangerous” is essential in the sentence and this fact will affect whether “that” or “which” is grammatically correct.)

In principle I agree with what TraceyG says. If it is a general question, use ‘what.’ If there is a preference or choice given or you want to elicit a specific response, use ‘which.’

But in practice, it is not so simple.

If someone asks, “What floor do you live on?” they are eliciting a specific response: on which floor? Which floor do you live on?

Likewise, if someone asks, “What grade are you in?” they are eliciting a specific response: in which grade? Which grade are you in?

So how do you know when to use ‘which’ and when to use ‘what’? That is a simple question to a more complex answer.

I would just note that in both cases a preposition is used: to live on a certain floor; to be in a certain grade.

In most cases, when the question is about ‘which’ specific setting or location: from which country, in which city, at which store, to which school, in which grade, on which floor, etc., so that it ends in a preposition, either ‘which’ or ‘what’ is acceptable, there is no difference in the type of response that is being elicited, yet I would say that most people prefer to use ‘what.’

All of the following questions can use ‘which,’ but I would say that ‘what’ is preferred:

I’m from Taiwan. What country are you from?

I live in Taipei. What city do you live in?

I shop at Breeze Super. What store do you shop at?

My daughter goes to Nei-Hu. What school do you go to?

My son is in the sixth grade. What grade are you in?

I live on the fifth floor. What floor do you live on?


side note:

Just as a point of comparison, I would like to point out that the Dutch always use welk/welke (which) in these types of questions:

Uit welke land kom jij? From which country do you come?

In welke stad woon jij? In which city do you live?

Bij welke winkel doe jij je boodschappen? At which store do you shop?

Op welke school zit jij? At which school do you sit?

In welke klas zit jij? In which grade do you sit?

Op welke verdieping woon je? On which floor do you live?

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How about asking someone’s birthday? When is your birthday? What date is your birthday? Which one is preferred?

Thank you!!

When is your birthday? (informal) The person will probably tell you the month and day, but not the year. If you want to know the year, you’ll probably have to ask, ‘What year were you born?’

What is your date of birth? (formal) The person is expected to state the month, day and year on which they were born.

There are other ways to ask when someone was born, but I would say those are the two main ways of asking.

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Thank you very much, brucenator!!!

You are very welcome, lilyyang!
By the way, if the person’s birthday is coming up fairly soon and you ask, “When is your birthday?” they might respond, “Next week” (or ‘this week’ or ‘day after tomorrow’ or ‘next month’ or whatever the case may be.)