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there are some oddities I have just dug up in a grammar book and in which you might be interested:

Marginal modal auxiliaries:

used to, ought to, need, dare

used to:

He usedn't to smoke.
He did not use to smoke.
He used to drink, did he not.
Did he use to drink?

ought to:

Ought I to stop smoking? Yes, you ought (to).
You oughtn't to stop smoking.
You do not ought to stop smoking.

dare, need:

may act as modals and full verbs.
The modal usage is restricted to non-assertive contexts, negatives, to if clauses.
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>He usedn't to smoke.
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http://forum.wordreference.com/showthread.php?t=24673
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Inchoateknowledgethere are some oddities I have just dug up in a grammar book and in which you might be interested:

Marginal modal auxiliaries:

used to, ought to, need, dare

used to:

He usedn't to smoke.
He did not use to smoke.
He used to drink, did he not.
Did he use to drink?

ought to:

Ought I to stop smoking? Yes, you ought (to).
You oughtn't to stop smoking.
You do not ought to stop smoking.

dare, need:

may act as modals and full verbs.
The modal usage is restricted to non-assertive contexts, negatives, to if clauses.

I think the grammar book you are using is confusing you more than helping you. In m opinion, I think you will probably beneift more by reading Reader Digest. I never heard people say "usedn't " nor "oughtn't" in my life. To me this is odd-ball English.
A grammar book I use lists the following as the modal auxiliaries:
can/could
may-might
will/would
shall/should
must
ought
and the following as modal-like auxiliaries:
had better
have got
get (to)
have (to)
be able
be supposed
be bound
I've never heard of usedn't, or You do not ought to stop smoking. I would say He used to not smoke and You should not stop smoking.
This is the book I study from.
Students: We have free audio pronunciation exercises.
"oughtn't" is still used in BrEng. Not sure about "usedn't," though.