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The header of psyco.sourceforge.net states:

High-level languages need not be slower than low-level ones.

Why use need not instead of do not need? What does it mean? Also, why no to before be?

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    also consider Brevity in the artful construction of language Sep 4 '13 at 13:27
  • Need not sounds more refined and formal.
    – user82307
    Jun 26 '14 at 17:54
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    This is subjuncitve mood. You can read this: web.cn.edu/kwheeler/grammar_subjunctive.html Jul 9 '15 at 11:56
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    @martinkunev That is incorrect. Those constructions are different (and some would say shouldn't be called 'subjunctive' anyway). Read Cerberus's correct explanation. Dec 9 '15 at 16:24
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    As Cerberus says, it's a usage of the modal 'need' (followed by the infinitive 'be'). 'You need not be present.' Compare 'You need not go.' / 'You must not be present.' You're confusing this with old-fashioned usages such as 'I insist that he be replaced.' (= 'I insist that he should / must be replaced.') Dec 9 '15 at 23:34
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There are two verbs need, which mean the same thing but use different constructions:

1.

He need not be concerned.

Need I be concerned?

This need is sometimes called a modal verb (although others find this term inconsistent): it always requires an infinitive without to; it doesn't have do-support in questions and negative sentences; and the third person singular (he/she/it) doesn't have -s. This is the need in your example. It is of the same type as must, will, shall, can, may, help, and probably a few uncommon cases.

Modal need is slightly old fashioned. Except in negative sentences and questions, it is less common in modern writing, except perhaps in certain fixed expressions (though the need in if need be is a noun).


2.

He doesn't need to call her.

Do I need to call him?

She needs to call him.

You need him.

This is the more common need, a regular verb (no 'modal'). If it is used with another verb, the infinitive with to is used. It always has do-support. It can be used without another verb, with a direct object (you need him).

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    +1 It doesn't seem that old-fashioned in the negative. Google Ngrams shows "need not" is still used much more often than either "needs not" and "does not need to". For the regular verb, you can see from the Ngram that "does not need to" is slowly replacing "needs not". Jun 10 '11 at 18:40
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    @Peter Shor: Need is also a noun. With that ngram, you have no way of excluding things like "there is a need not to generalize".
    – Kosmonaut
    Jun 10 '11 at 18:48
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    @Kosmonaut: I checked a sample, and the vast majority indeed seem to be need being used as a modal verb. Jun 10 '11 at 18:51
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    If you put a "He" (capitalized so it goes at the beginning of a sentence) in the Ngram you get nearly the same results. I don't see how there could be any false positives in this set. Nov 24 '12 at 18:18
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    Historical note: "need not" replaced "tharf not" during Middle English. The verb tharf was also a modal used only in the negative, and is cognate with the German modal verb dürfen, meaning must. Oct 23 '13 at 15:02

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