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General question about when to use "is" and "does" as I keep interchanging both of them.

In the sentence

"What time does the pharmacy open?"

Why can't I write this:

"What time IS the pharmacy open?"

I know that

"when is the pharmacy open?"

is correct so does

"When does the pharmacy open?"

work as well?

I am having trouble learning the difference of when to use "is" instead of does. Are there any instances of when they are interchangeable such as "When is the pharmacy open" and "When does the pharmacy open?" mean the same thing? Should I always assume that they are never interchangeable?

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    Your question is tagged "active vs passive". Additionally to all the correct answers, please note that both sentences in question are active.
    – rexkogitans
    Dec 27, 2020 at 9:52
  • Passive: "What time is the pharmacy opened?" But the suffix -ed is pronounced softly by some speakers, and other times, in fast speech, it may seem to be omitted altogether without affecting meaning. If we change the verb "open" to a different one, such as "close" then it's "When are the shops closed [for Christmas]?"
    – Mari-Lou A
    Dec 28, 2020 at 12:23
  • Both are proper questions, they just have (slightly) different answers.
    – RBarryYoung
    Dec 28, 2020 at 13:24
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    to be describes a state, to do describes an action.
    – njzk2
    Dec 28, 2020 at 23:15

7 Answers 7

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Confusion around use of ‘is’ versus ‘does’ is exceedingly common among people learning English as a second language, as it’s a distinction that a large number of other languages make through context (either by usage of specific forms for other words in the sentence, or by choice of words in the sentence).

The difference, once you know it, is actually pretty simple.

  • ‘does’ and its various forms always involve an activity to refer to. Sometimes it is an actual verb or verb phrase, sometimes it’s a pronoun or other syntactic placeholder (such as ‘this’ or ‘that’), other times it’s simply implied from context (such as in ‘do <adverb>’ constructs), but there’s always an activity involved.
  • ‘is’ and its various forms instead refer to a state of existence. If there’s an associated activity, it is (almost) always in the form of a continuous tense verb (for example, ‘He is winning.’). Usually though, it’s either a noun or an adjective being used to describe the subject of the sentence.

Given this, there is usually a difference in meaning between using ‘does’ and using ‘is’ when you’re grammatically able to use both (though note that in some dialects, the ‘is’ form of a sentence may also be used to mean the same as the ‘does’ form).

The important difference here for your question is that ‘is’ refers to a state of existence, while ‘does’ refers to activity. Given this:

  • ‘When does the pharmacy open?’: Asks at what time the pharmacy goes from being closed to being open. ‘open’ in this case is a verb, referring to the act of becoming prepared to conduct business. The activity referenced by ‘does’ here is the change in state of existence described by the verb ‘open’.
  • ‘When is the pharmacy open?’: Asks what times the pharmacy is in the state of being ‘open’. Unlike above, ‘open’ is an adjective in this one, describing the state of being prepared to conduct business.
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    If one wanted to super-precise, with "does" indicating a change in state, the answer to "When does the pharmacy open?" is a specific time, e.g. "8 am." By contrast, "When is the pharmacy open?" would more appropriately be answered by the entire range, e.g. "8 am to 10 pm on weekdays, 8 am to 6 pm on weekends."
    – T.J.L.
    Dec 28, 2020 at 13:26
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What time is the pharmacy open?

I would assume you are asking about the time during which the pharmacy is open (its working hours), and would reply with

We are open from 9 to 17.

(I am being a pharmacy assistant here, thus we)

If I hear

When does the pharmacy open?

I would think you are asking about the opening time (when the pharmacy starts to do its business) and would answer with

The pharmacy usually opens (up) at 9 o'clock in the morning.

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    to be honest, I - a US speaker - might add that "is" could also be just the opening time, like the example for "does". Maybe that would depend on whether or not it is open already, or maybe it feels less personal
    – Mike M
    Dec 27, 2020 at 12:37
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    It might be helpful to contrast with the time of closing: What time does the pharmacy close? What time is the pharmacy closed? The action versus state contrast is enhanced by the need for the different word form.
    – Paul_Pedant
    Dec 27, 2020 at 18:16
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    Not sure that many people (other than military types and a few others) would identify with "open from 9 to 17". Most people operate on a 12-hour clock, so "9 to 6" would be more universally understood. "9 AM to 6 PM" if you want to be less ambiguous, though that's unnecessary since it's reasonable to assume a shop is open mostly during daylight hours.
    – Darrel Hoffman
    Dec 28, 2020 at 15:17
  • @DarrelHoffman 17:00 = 5pm, not 6pm, which I guess illustrates your point that people don't really use 24hr clocks very often. I will say that 24hr is not unusual in the UK, but I know it's less common in the US
    – Steven Waterman
    Dec 28, 2020 at 17:21
  • @StevenWaterman Derp. I thought I checked that. That's what I get for posting before caffeinating.
    – Darrel Hoffman
    Dec 28, 2020 at 17:24
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Your confusion here is because the English verb "open" can be both a verb:

I opened the door. / I did open the door. (the second uses "do support")

And an adjective.

This is an open door. / The door is open.

Now we can say, using the verb

The pharmacy opens at 8:00

When I form a question I use the "do" auxillary, and swap the subject with the auxillary verb, and put the question word at the front

The pharmacy opens when → The pharmacy does open when → Does the pharmacy open when → When does the pharmacy open?

But I can express a similar idea using the adjective. Swap the subject and the "be" verb, use a question word at the front.

The pharmacy is open from 8:00 → The pharmacy is open when → Is the pharmacy open when → When is the pharmacy open?

English is strange because the same word can sometimes be both an adjective or a verb, and the only way to tell is to look at the other words in the sentence.

Other verbs can't be used as adjectives. Eg "eat"

What do you eat for lunch? (correct)

What is you eat for lunch? (not correct)

And other adjectives can't be used as verbs. Eg "happy"

Why does he happy? (not correct)

Why is he happy? (correct)

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Why can't I write this: "What time IS the pharmacy open?"

You most certainly can.

In this case, "is" is a state of being: the pharmacy is in the state of openness between 8AM to 9PM.

"When does the pharmacy open?"

That also works, because the pharmacy is "doing" (where "do" is the root of "does" and "doing") something: it is opening its doors at 8AM.

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    "in the state of openness" sounds a little weird and "opening it's doors" should be "opening its doors"
    – Andrew Tobilko
    Dec 27, 2020 at 12:28
  • @AndrewTobilko sure "in the state of openness" sounds weird, which is why we don't say it, but that state of being is in fact what the "be" verb in "the pharmacy is open" and "What time IS the pharmacy open?" means.
    – RonJohn
    Dec 27, 2020 at 17:44
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Here are two sentences that might help make the difference clear.

Is the pharmacy open at 9 am? Yes, it opens at 7 am.

Does the pharmacy open at 9 am? No, it opens at 7 am.

"Does" in a sentence refers to the act of opening, so just the exact time of opening; "Is" in a sentence refers to the state of being open.

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Based on your name, I assume that your mother tongue is Spanish, so I want to give translations of the two sentences:

"When is the pharmacy open?" = "¿Cuándo está la farmacia abierta?" ("open" is an adjective)

"When does the pharmacy open?" = "¿Cuándo abre la farmacia?" ("open" is a verb)

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    This site does not encourage translation. If are going to answer, please explain everything in English.
    – fev
    Dec 27, 2020 at 15:00
  • @fev I think he checked the username and he assumed the OP is a spanish speaker and that it would be helpful to provide tranlsation to OPs mother tongue, but yup rules are rules
    – hocikto
    Dec 27, 2020 at 16:47
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    @fev. I didn't want to give an explanation. There are others that do it better than me. But I thought that a translation of the sentences might help in understanding the difference. Of course the main language in this site should be English, but comparisons with other languages can be helpful.
    – md2perpe
    Dec 27, 2020 at 19:24
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    Well, there are already several other answers, so supplementing them with this should be fine. Spanish is a pretty common language anyway. It would definitely be a problem if this were the only or almost the only answer; but when there are several others, it should help add icing to the cake.
    – Panzercrisis
    Dec 28, 2020 at 16:40
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    FWIW, this answer also contains the explanation in English. It's concise (which is often a good thing for people who are not fluent), but this answer directly offers an explanation in English, very quickly addressing the verb vs. adjective usage of the word "open" - not simply translations.
    – Panzercrisis
    Dec 28, 2020 at 16:44
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What time does the pharmacy open?
At 9.00am.

What time IS the pharmacy open?
Each day from 9.00 till 5.00

When is the pharmacy open?
Each day from 9.00 till 5.00

When does the pharmacy open?
At 9.00am.

It is open every day.
Is it?

It opens at 9.00am.
Does it?

Yes, I think you should assume that they are never interchangeable. I can't think of a context where they would be interchangeable.

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