-n't

• -'nt (obsolete)

Univerbation of not and some preceding words (see usage notes) and following elision of medial vowel, or univerbation of n't and some preceding words. Compare n't.

• IPA^(key): /(ə)nt/

-n't

1. (no longer productive, unless humorous) Negates the meaning of the clause in which it occurs.

   It is a beautiful bouquet! You needn't've bothered, thank you.

• This contraction does not receive stress, even for contrast: either you DID or you DIDn't.
• The suffix -n’t can only be added to auxiliary verbs, including dare and need in certain uses (see daredn't), as well as main verbs be (in almost all uses) and have (in some uses). Indeed, in some dialects, not all auxiliary verbs accept -n’t; for example, mayn’t is present in some dialects and absent in others.
• Some verbs change their form when -n’t is added; for example, shall + -n’t is usually shan’t, and am + -n’t is frequently aren’t or ain’t (though all three of these are dialect-dependent).
• Though verbs with -n’t are usually considered contractions of versions using the adverb not, grammatically they behave somewhat differently. For example, when subject and verb are inverted, -n’t remains attached to the verb, whereas not does not:

  Isn’t that difficult?

  Is that not difficult?

• Semantically, -n’t may have either “high attachment” or “low attachment”, depending primarily on the verb. For example, “I can’t leave” means “It is not the case that I can leave” (usually “I am unable to leave”), whereas “I shouldn’t leave” means basically “I should stay” (which is a narrower statement, and therefore a stronger one, than “It is not the case that I should leave”). (“I can stay”, by contrast, is very different from “I can’t leave.”) Similar variation is seen with the adverb not, as well as various other negative constructions.

• TN, Tn, tn