Sentence Choice – Why Write ‘Does’ Instead of ‘Is’ in ‘What Time Does/Is the Pharmacy Open?’

active-vs-passivesentence-choice

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?

Best Answer

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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