[Grammar] need not to

[Aiwen]

I can say: "I need not to know"
However, I can also find constructions without "to": "I need not go" (Thomas Hardy).
Is there any rule that steers the use of "to" after an auxiliary verb? Which is the rule or rules behind constructions as: I need to do, I can do, I have to do, I avoid doing, let him do, etc.?

 

[5jj]

'Need' can function as a full verb, followed by a to-infinitive:

He needs to know. He doesn't need to know. Does he need to know?

It can also function as a modal, followed by a bare infinitive. This is usually only in negative and interrogative constructions:

[STRIKE]He need know[/STRIKE]. He needn't know. Need he know?
I don't think he need know.

 

[Raymott]

I can say: "I need not to know"
However, I can also find constructions without "to": "I need not go" (Thomas Hardy).
Is there any rule that steers the use of "to" after an auxiliary verb? Which is the rule or rules behind constructions as: I need to do, I can do, I have to do, I avoid doing, let him do, etc.?

You'd generally say "I don't need to know", if you mean you don't have a need to know. Or, "I need not know".
I would keep "I need not to know" for instances where your need is to not know about something.

"You need not look at me like that!" - "You don't have to look at me like that!"
"You need not to look at me like that!" - "You must not look at me like that!"

 

[Aiwen]

Raymott,
thank you for your answer. It is very important for a non-native speaker to catch these subtleties to which a native speaker reacts unconsciously. Let me check whether I understood:

"I need not to know the truth" means that I want to ignore the truth (maybe because it could hurt me).

A doubt:
In this case, when speaking, should one stress "need"?
"I need". What do I "need"? "not to know the truth".
If one stresses "not" would the same meaning be transmitted? "I need not" What do I "need not"? "to know the truth".
​

"I need not know the truth" or "I don't need to known the truth" means that it not necessary for me to know the truth, but, if I would know it, it wouldn't make any difference.

Is it right?

 

[Barb_D]

In this rather odd case (the truth is hurtful, somehow) you would stress the "not" because it's unexpected.

I need to NOT know the truth.

(People still argue about splitting the infinitive, but in this case, I don't feel it is. It's almost as though "not-know" is a verb meaning "be ignorant of.")

I do not need to see your homework. (It's not important for me to see it..)
I need not see your homework. (Not a typical American construction, but to me, the same as above.)
*I need not to see... (I would call this a non-standard word order.)
I need to NOT see your homework. (I can't see it. If I do, I'll know you cheated, or something that I can't know about.)

 

[Raymott]

Raymott,
thank you for your answer. It is very important for a non-native speaker to catch these subtleties to which a native speaker reacts unconsciously. Let me check whether I understood:

"I need not to know the truth" means that I want to ignore the truth (maybe because it could hurt me).
That's right. Or as Barb said, "I need to not know the truth". In either case, this is not such a common expression. More likely one would say, "I'm not allowed to know that", "I'd prefer not to be told about that", etc.

A doubt:

In this case, when speaking, should one stress "need"?
"I need". What do I "need"? "not to know the truth".
If one stresses "not" would the same meaning be transmitted? "I need not" What do I "need not"? "to know the truth".
​

"I need not know the truth" or "I don't need to known the truth" means that it not necessary for me to know the truth, but, if I would know it, it wouldn't make any difference.

Is it right?
Yes.

But the meaning is more often in the context or in the intonation.
If my defence lawyer said, "If you've done anything illegal in obtaining that information, I don't need to know about it", I would assume that he doesn't want to know, ie. meaning 1. from above.
I hope that's not too confusing!

 

[5jj]

Write that large:

But the meaning is more often in the context or in the intonation.

This is so important in so much of English, and it is too often overlooked.