[michèle 2]

Hello everyone,
I was asked today if there are any differences between "needn't and don't need to." She was told that needn't and don't need to are used in different situations. But she didn't understand what her teacher said. And for me they have exactly the same meaning
Can you help?

[susan53]

First of all she needs to understand the difference between the two forms - ie need in the negative can be used either as an auxiliary verb (needn't do) or as a main verb - which means that in the negative it needs the auxiliary do and is followed by to - don't need to)

Given that, it's clear that the auxiliary form can't be followed by a noun - modal auxiliary verbs can only be followed by other infinitive verbs. So, if you're talking about cheese for example, you have to use it as a main verb :
We don't need any cheese.
you can't say
*We needn't any cheese.

Similarlarly, when need is followed by an -ing form with passive meaning, the negative can only be used as a main verb. And for the same reason - modal auxiliaries can only be followed by infinitives so the gerund is impossible. Thus :
It doesn't need doing - is OK but *It needn't doing is not possible

However, when need in the negative is followed by an infinitive then both forms are equivalent in meaning and register :
We don't need to do it = We needn't do it. No difference at all - and if that is what was being taught, you're right and the other teacher was wrong.

Even in the past it's the same : we didn't need to do it = we needn't have done it. Both could be followed by either So we didn't or But we did.

Don't know if that helps. It's difficult without knowing the exact examples the teacher was talking about. Any idea?

[michèle 2]

Thanks a lot Sue
My student is coming next Thursday so we'll have the examples.
I'll post them as soon as I get them.
Thanks again

[susan53]

Bad weather in France, huh? Cold but sunny here!

[michèle 2]

Hi everyone
Hi Sue

Here are the examples:
You needn't remind me.
You don't need to book.
Thanks for your help

[susan53]

For both examples the meaning remains the same whether the modal construction or the main verb construction are used.
Sue

[michèle 2]

Thanks Sue, it's very clear.

[Bagga]

Just one point though, with regard to the examples of negative need in the past:

we didn't need to do it = we needn't have done it

That example has meanings that may be slightly different.


we didn't need to do it can mean that a task was set, at a time in the past, but it wasn't necessary for us to do it. (That is to say, the task was scheduled to be done AFTER the point in time that the task was set.)

we needn't have done it means that the task had been completed, but it wasn't necessary. (That is, we wasted all that time and effort when we could have been down the pub discussing the finer points of grammar. Dang!)

Just my two penn'orth.

[susan53]

I think it's more complex than that. There are actually three possibilities :

1. We knew it wasn't necessary so we didn't do it.
We didn't need to have any vaccinations when we went to Morocco.
Here only didn't need to is possible.

2. We knew it wasn't necessary but we did it anyway. Here both are possible and there's no difference in meaning.

a) We didn't need to go to the meeting, but we knew John would be there and we wanted to see him, so we went anyway.
b) We needn't have gone to the meeting but we knew John would be there and we wanted to see him, so we went anyway.

3. We didn't know it wasn't necessary so we did it and found out later. Again both are possible.

a) What an idiot I was! I spent the whole weekend studying and I didn't need to at all - the exam's next month, not this month!
b) What an idiot I was! I spent the whole weekend studying and I needn't have done it at all - the exam's next month, not this month!

So - needn't have always means that the event happened, whether we knew about it in advance or not. Some examples I got by Googling it were :
he needn't have died, she needn't have worried, you needn't have bothered - in all cases it happened but wasn't necessary.

didn't need to on the other hand may mean either it happened or not. Again examples from Google include :
I didn't need to see that! and The things they carried and didn't need to. - ie it happened
Solved all my gift problems and didn't need to traipse through loads of shops - ie it didn't happen

Michèle - I think when your student's teacher said there was a difference, it was this s/he was thinking of - but s/he didn't realise it's valid only in the past, not in the present where the two constructions are identical.