I just came across this weird use of "need not" on Twitter:
Madam/sir,
My daughter is stuck in Uk . She has lost her BRP . She is difficult to return back India home [sic]. Please help
In response, India in the UK says:
She need not worry. She should stay where she is. Just tell her to keep herself safe. Please delete your tweet.
Shouldn't it be "she doesn't need to worry" or "she needs to not worry" given that the subject is "she" (singular)? Or is this some kind of grammatical construction I don't know? I believe who wrote it was a native speaker of English and they might be correct. Can someone explain this please?
Best Answer
That is fine. Need in that sentence is used as a modal auxiliary and we use the bare infinitive1 after modal auxiliaries. It's called a 'semi-modal' because it can act as both a modal verb (like should, can, might, may) and a normal/lexical verb (as in She doesn't need to worry).
Try replacing the need with another modal auxiliary (for example should):
(This is just for comparison and doesn't mean need not and should not are the same. This use of need not mean there's no obligation.)
It behaves the same as other modal auxiliaries and we always use the bare infinitive after them. However, unlike other modal auxiliaries, need is restricted to negatives and interrogatives.