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 Commented Sep 4, 2013 at 13:27
  • Need not sounds more refined and formal.
    – user82307
    Commented Jun 26, 2014 at 17:54
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    This is subjuncitve mood. You can read this: web.cn.edu/kwheeler/grammar_subjunctive.html Commented Jul 9, 2015 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. Commented Dec 9, 2015 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.') Commented Dec 9, 2015 at 23:34

1 Answer 1


There are two verbs need, which mean the same thing but use different constructions:


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).


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". Commented Jun 10, 2011 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
    Commented Jun 10, 2011 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. Commented Jun 10, 2011 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. Commented Nov 24, 2012 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. Commented Oct 23, 2013 at 15:02

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