I have come across need to do something and need do something. My question is what's the difference between each other? My grammar book doesn't mention it

  • The only time I can think of that you would omit the to is in the question form. "Need I ask?" "Need you make so much noise?" Oct 31, 2019 at 9:10
  • Agreeing with the above, you might see "need do" in some contexts, particularly less formal ones ("what I need do" gets plenty of Google hits), but "need to do" is always correct, whereas "need do" might sound less formal or incorrect to some.
    – Stuart F
    Oct 31, 2019 at 10:28
  • I find more places where the "do" gets dropped than where the "to" does. "Clean your room!" "Do I need to?"
    – puppetsock
    Oct 31, 2019 at 14:47
  • 1
    Are you sure it wasn't "I need not do something"? We only drop the to in negative sentences. Oct 31, 2019 at 21:58
  • 2
    @PeterShor has the right of it. When you're finding anomalies in English grammar, look around for negatives. They can change everything. In this case, the negation allows need (a semi-modal) to act like a true modal auxiliary, and take an infinitive complement without to. Oct 31, 2019 at 22:16

1 Answer 1


I think you should use "to do".

'do' is an auxillary, action verb: "you need to do [the thing]".

I have never hear a native english speaker use the: "I need do something." form.

Auxiliary verbs add functional or grammatical meaning to the clauses in which they appear. They perform their functions in several different ways:

  • By expressing tense ( providing a time reference, i.e. past, present, or future)
  • Grammatical aspect (expresses how verb relates to the flow of time)
  • Modality (quantifies verbs) Voice (describes the relationship between the action expressed by the verb and the participants identified by the verb’s subject, object, etc.)
  • Adds emphasis to a sentence

Auxiliary verbs almost always appear together with a main verb, and though there are only a few of them (do, be, and have are the main ones), they are among the most frequently occurring verbs in the English language.

  • One needn't include the to when used in negation.
    – tchrist
    Dec 1, 2019 at 23:42
  • "I need not do that..." - quite agree.
    – NeilB
    Dec 2, 2019 at 17:59

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