Is the following sentence grammatically correct? (I found this sentence on a friend's wall on Facebook)

How many psychologists does it take to change a light bulb?

or it should be

How many psychologists are needed to change a light bulb?

  • 30
    It is an old joke that is always in this format. One, but the light bulb really has to want to change. How many blondes does it take to change a light bulb? Four. One to hold the bulb and three to turn the ladder. These jokes are decades old.
    – WRX
    Commented Mar 25, 2017 at 21:09
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    @Max I simply saw it in a friends wall, and I know that he sometimes make mistakes in English + it's not a structure that I met in the past + For me as NNE speaker it doesn't look like a natural English based on my experience in the language. I'm surprised to know that it's something well known. I always learn new things:) Commented Mar 25, 2017 at 21:38
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    An excellent learner’s question. I’ve heard “light bulb” jokes for years, so I never really thought about the grammatical construct. But I can see why an English learner might sense that the wording seems a bit peculiar. Sometimes ubiquitousness leads to acceptability, as in this case.
    – J.R.
    Commented Mar 25, 2017 at 23:44
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    @J.R. This goes way beyond the set phrase in the joke, though--the usage of it for an indeterminate, vague referent is extremely common. Commented Mar 26, 2017 at 2:17
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    I don't think this is "hallowed by long usage". ""Does it take" is idiomatic in other contexts ("what does it take?"). And more generally as noted below "it takes" very much so. Commented Mar 26, 2017 at 8:25

5 Answers 5


Both of these are perfectly correct. You could also say "How many psychologists are necessary to change a light bulb?" or "How many psychologists are required to change a light bulb?"

However, as Willow pointed out, "How many X does it take to change a lightbulb?" is a formulaic phrasing for the setup line of a group of similar jokes. It's always said that way.

  • 18
    "The ones that can't afford office staff." (That's the answer to the one with the "required to" phrasing.)
    – msouth
    Commented Mar 26, 2017 at 5:32
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    @msouth took a second to get that one. Might be a good separate question. Commented Mar 27, 2017 at 4:59
  • Bear in mind too that because this is the setup for a joke, the assumption is that you only have psychologists at your disposal. Nobody ever seems to have a maintenance guy in these jokes.
    – timbstoke
    Commented Mar 27, 2017 at 9:02
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    @timbstoke I think it's more of a reference to the fact that the "required to" phrasing has two valid interpretations - one the same as the "does it take to" phrasing, and the other meaning something like "Of all the psychologists in the world, how many of them need to change light bulbs"?
    – Muzer
    Commented Mar 27, 2017 at 9:58
  • @Muzer is right, I had just noticed the second way that "required" could be interpreted there and made a joke about it. I like timbstoke 's observation about the apparent dearth of maintenance personnel in these jokes; might be able to parlay that one into a punchline like "none--that's a union job". Although I would be surprised if the union gag hasn't already been employed. Also: this being ELL, I'm glad Muzer followed up with the detailed explanation, because that will probably help with the original goal of learning something about phrasing and meaning in English. SE peeps FTW.
    – msouth
    Commented Mar 28, 2017 at 2:16

"It takes x to y" is extremely common, and I'm surprised that you haven't met it before. It is certainly not confined to light-bulb jokes! It means "x is necessary in order to y." Here are some examples:

It takes courage to do what you did.
It takes a lot to rattle her.
It takes at least a week to acclimatise to the altitude.

And of course:

It takes two to tango.

  • That's a different formulation. "How many X does it take to Y?"
    – jpaugh
    Commented Mar 27, 2017 at 16:20
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    Thatt's just the interrogative version of "It takes three (or however many) psychologists to change a light bulb."
    – TonyK
    Commented Mar 27, 2017 at 16:36
  • Yes, and if you focus on the interrogative version in your answer, you will reach a wider audience, in the context of this question -- namely those who can't do that conversion mentally, yet.
    – jpaugh
    Commented Mar 27, 2017 at 19:18

Yes, because "take" can mean "require." If three psychologists are standing in line, it's like taking one out of the line to change the light bulb. "It" standing for the task. It's informal, but it is still correct as a sentence.

  • 10
    Also e.g. "It takes one to know one", "It takes two to tango", "It takes a village to raise a child"
    – wjandrea
    Commented Mar 26, 2017 at 3:06
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    I don't think this interpretation is quite correct. Take doesn't mean "take out of" in this context; we're not taking one of the psychologists, we're requiring all of them.
    – stangdon
    Commented Mar 26, 2017 at 13:19
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    "It" doesn't stand for the task: it's the same dummy pronoun that you see in sentences such as "It is raining." Commented Mar 26, 2017 at 15:10
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    @user2338816: But you can't say *"How many does changing a light bulb take to change a light bulb?". This is a very typical example of it-extraposition; the it itself is meaningless, and just fills the syntactic gap left by extraposing the subject.
    – ruakh
    Commented Mar 27, 2017 at 1:25
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    @user2338816: You are assuming that "it" serves the same role in "How many does it take?" as in "How many does it take to change a light bulb?". That assumption is mistaken -- note that only in the former can "it" be replaced by "that" -- so all arguments based on that assumption are flawed.
    – ruakh
    Commented Mar 27, 2017 at 3:36

You appear to have misidentified the subject of the sentence. In questions, word order is often inverted.

The subject of the sentence is the word "it," not "many" or "psychologists." The verb must agree in number with the subject. If you were to answer the question, you would say "It takes five psychologists to screw in a light bulb." Hence the correct word to use is "takes."

The issue is likely that the word "it" does not actually refer to anything. This is a grammatical quirk of English. All sentences must have subjects. The word "it" in this sentence is a non-referential subject. More information may be found in this English Language Usage question.

  • 1
    It's not so much a quirk as it is the English construction for an impersonal verb.
    – chepner
    Commented Mar 26, 2017 at 12:23
  • You haven't actually answered the question as posed: I see nothing in the question about what the subject is, or anything to do with word order, verb number, or what "it" is.
    – R.M.
    Commented Mar 26, 2017 at 13:18
  • The question seems to be "why does while I have 'many' on the other side?" because of the bold text. IMO it answered it well. It explained why the first quote is correct. Maybe one could add that the other OP's suggestion is also correct.
    – Xenos
    Commented Mar 26, 2017 at 13:24
  • I think this is a good answer, since it actually explains the grammatical structure of the sentence, where the others basically say "that's just how it is."
    – Mr Lister
    Commented Mar 27, 2017 at 9:41
  • Your answer seems accurate, but @R.M. has a good point: it may be difficult to understand, unless you can tie it back into the question more.
    – jpaugh
    Commented Mar 27, 2017 at 16:24

How many does it take - implies that there may not be a specific, immutable number. How many is needed - implies that there is an actual answer that can be given with certainty.

Because psychologists endeavor to help a person achieve change, understanding, and since this process does not follow a predictable path, you cannot answer, "How many are needed?" It remains for the goal to be reached before you can answer the question.

  • 10
    This is just plain false. Commented Mar 26, 2017 at 8:14
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    You've made a few grammatical errors in your answer. There's one in the first paragraph, second sentence, first clause, for instance.
    – wizzwizz4
    Commented Mar 26, 2017 at 8:51

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