He is about to open the door.

What part of speech is "about to" in this sentence? Is it an adjective, or an adverb?

I am really confused, and somewhere I read that it is idiomatic as well.

  • The to is an infinitive marker for the verb [to] open. As for about, taking note of similar forms such as He is about finished I'd say it adverbially modifies the following verb form, but what do I know? Feb 13, 2016 at 13:31
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    I'd say about is pretty clearly the ordinary preposition. The object of the preposition is the infinitival clause to open the gate, and the entire preposition phrase is a figurative "locative", describing the subject's location in time, exactly as in He is on the verge of opening the gate. Feb 13, 2016 at 13:45
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    Figurative locatives insofar as they contribute to verbal aspect could be understood as verb modifiers, no? How do they differ from "He was late to arrive"? Feb 13, 2016 at 15:07
  • About is an adjective meaning intending or ready. It's used in the form be + about + to infinitive + something as an idiom, that means someone is /was ready or intending to do something or someone is going to do something soon or something is going to happen soon.
    – Khan
    Feb 13, 2016 at 15:16
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    @Khan: so you would take about as a predicate adjective with an infinitival clause complement? Feb 13, 2016 at 15:17

1 Answer 1


The word about is an adverb meaning:

very close to doing something

If you omit about, the remaining sentence will be

He is to open the door.

which is a so-called "be to-infinitive" construction which is mainly used to indicate a future event, intention or schedule.

"He is to open the door" doesn't indicate when he will open the door. However, if you add the adverb about, it indicates he will open the door very soon.

Be about to is a more idiomatic expression than be soon to.

Edit: If about is either a preposition or adjective, they cannot be omitted. If you contrast "I was about to call you, but something urgent came up" with "I was to call you, but something urgent came up", you will notice there is no big difference.


  • Different people have different thoughts. It really confuses me. Still I am looking for the correct explanation. Someone says, it is preposition. Someone says, it is adjective. Someone says, it is idiom. Someone says, it is adverb. Your these statements really confusing me. Feb 13, 2016 at 16:22
  • @Khan, I have also looked it up in various dictionaries, but I got just an answer. "About"is an adjective there. Feb 13, 2016 at 16:28
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    I think this answer makes a good case for saying about is used adverbially in OP's context, but at the end of the day coming down solidly in favour of some specific "part of speech" here is about as useful as arguing over the "true" nature of light. At the basic level with simple examples, particle / wave and adverb / preposition may be useful distinctions to make regarding physical/syntactic phenomena, but beyond a certain point it becomes counterproductive because the classifications don't correspond to exactly how the "real" things function anyway. Feb 13, 2016 at 16:57

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