difference between aren't, ain't and amn't

aren't - () short form
1 are not
     ----- We aren't leaving tomorrow.
2 (in questions) am not
     ---- I'm invited, aren't I?
amn't - ()
 short form

(Scottish English, Irish English, non-standard)

 

am not

ain't - () short form
(non-standard orhumorous)
1 am not/is not/are not     ---- Things ain't what they used to be.2 has not/have not    ---- I ain't got no money.    ---- You ain't seen nothing yet!

Tag question - amn't I? - aren't I? - ain't I?

• Well, the person asking for help did not specify if he is talking about written or colloquial language. Of course if you say "I'm late, am I not?" you tend to sound like Mary Poppins, but in written language you are certainly going to find such things.
  I´ve heard only "aren´t I" from English speaking colleagues, and also when I lived in Ireland, but, even though "amn´t I" does not turn up any longer in spoken English, the Heritage dictionary still considers it correct, and actually "amn´t" was still available somewhere in my brain.
  Reread the original message, the question is not about the construction "I am not late, am I?" (negative followed by positive and positive by negative). He is asking wether "am I not" or "aren´t I" is the correct one. 

• The correct form is "am I not." The verb needs to agree with the subject, so "aren't I" is certainly incorrect. Because "amn't I" sounds awkward, the best choice is "am I not," which is less awkward. It's basically the best of three evils.

Amn't I or aren't I ?

(I'd like to ask you please what question tag is correct, please, if I state :

I'm a truefriend of yours, amn't I ?

or

I'm a true friend of yours, aren't I ?)

• "aren't I" is correct. Another common variation is "ain't I" but some consider it incorrect.
  
  Hope it helps.

• I think both are possible depending on the region. But the latter is more common.

• The right answer is "aren't I" , because am+not= aren't . There's not a word like amn't.

• As it has been mentioned already, "aren't" is the correct choice.
  My tongue gets tangled when I try to pronounce "amn't".

• Aren't is the standard version, but amn't I is very common in Irish English and can therefore be said to be correct in spoken language atleast regionally. So no, amn't I isn't made up, it is just very uncommon outside of Ireland.

Why “ain't I” and “aren't I” instead of “amn't I”?

(Why do we say "ain't I" or "aren't I" instead of "amn't I"? What's the history of this usage? Are there any other similar patterns in English?)

• Historically speaking, both ain’t and aren’t are probably descended from an’t, recorded during the late C17 as the regular contraction. Sound changes of the C18 affected the pronunciation of the vowel "a" before nasal consonants, raising it in some dialects, and lowering and retracting it in others. While ain’tis a product of the first process, aren’t represents the second in terms of British (r-less) pronunciation – though not in general American. If only an’t was still available, it would avoid the grammatical discomfort and provide a nonstigmatized alternative to ain’t.

• The contraction aren't is used in standard English to mean "am not" in questions, as in "I'm right, aren't I?" Outside of questions, it is incorrect to use aren't to mean "am not" (for example, "I aren't going" is clearly wrong). The nonstandard (although logical) form amn't is restricted to Scottish, Irish, and dialect use.

Aren't I? (vs. "Amn't I?")

Q:

Why can't I say, "I'm right, amn't I?" using a tag question?

A:

Various grammar references note the illogic of aren't I as a tag question, but all describe its existence.

As a very formal alternative, you could use am I not, as in:

I'm a human being, am I not?

As well as the conversational:

I'm a human being, aren't I?

Some grammar references show that ain't I has historically been only marginally acceptable. Celce-Murcia and Larsen-Freeman (The Grammar Book, Heinle & Heinle, 1999, p. 218) suggest that aren't I arose from the "strong social and educational stigmas against the use of ain't."

Whatever its background, aren't I is indeed the current colloquial tag ending for the first person singular.

Aren't I? (vs. Am I not?)

Q:

What's the difference between: "I am right, aren't I? " and "I am right, am I not?"

Which one is more correct?

A:

Aren't I is colloquial and informal, as in "I'm a human being,aren't I?"
Am I not is quite formal, as in "I'm a human being, am I not?"

Both are correct.