The word "need" has a literal, informational meaning, and besides that it also accomplishes several other communicative tasks.
Usually "need" is used as a normal verb to express necessity.
Need can be a modal verb. It is more common in British English.
- You needn't come to that meeting.
- Need I say why?
- That is the only meeting you need attend.
You need attend that meeting.
"Need" plus a verb with -ing has the same meaning as a passive infinitive.
|Need + verb -ing||Passive infinitive|
|The dishes need washing.||The dishes need to be washed.|
|My sheets need changing.||My sheets need to be changed.|
|The bushes need trimming.||The bushes need to be trimmed.|
Saying someone need not have done something suggests that there was no reason to do it, that it was a bad idea. It differs in that respect from "did not need to have done."
|You needn't have given me that!||(I don't need your gift or I don't want it.)|
|You didn't need to give me that!||(I am flattered to receive your gift.)|
Including the word "never" adds emphasis: someone need never have done something.
|You needn't have told me.||(I didn't want to hear that.)|
|You need never have told me.||(Hearing that was very upsetting.)|
Using "need" in the present tense is often used to talk about obligation in the future. In particular, it can be used to give commands indirectly.
- You'll need to finish your homework.
- You'll need to come to my office.
Using "need not (do something)" grants permission not to do something at that moment. In this case, "need" is a modal verb. In a case where the listener might assume that they are obliged to do something, "need not" explicitly removes that obligation. This differs from using "need" as a regular verb, as in "You do not need to do something."
|You needn't pay for coffee.||Put away your wallet.|
|You do not need to pay for coffee.||It's free.|
"Need not" may also be used to equal "might not be." That is, it means that the possibility is less than 100%.
- I'm sure she went to the wrong place. - She need not have: maybe she is just running late.
- That face must mean that he hates me. - He needn't feel that way about you. Maybe he just remembered something unpleasant.