Grammatical dilemmas: "Amn't"; "Aren't I?", and others

1. People differ about what is the standard contraction for “am not”. All English speakers are taught that, unlike with "is not" and "are not", there is just no contraction for "am not".

The truth is that in some English dialects people use the contraction “amn’t”, but its use is considered totally unusual and weird outside such places in Ireland and Scotland.  Others simply prefer to use the expression “ain’t”, which many people consider very informal or slang.       

2. People also may differ about what should be the structure of negative questions with the verb to be. This has to do with question tags as well. Expressions without contractions, like “Am I not…?” “Is he not…?”, or “Are you not…?” are grammatically correct, but they are unusual in ordinary conversations in the United States. However, they are more used in the United Kingdom. These forms were more used in the past, (around the 17^th century), that’s why you could find them especially in literary works, (e.g. books from Jane Austen, William Shakespeare or some translations of the Bible). People in the U.S. may consider these expressions very poetic and formal, but they may be more common in other countries, including Australia.

The structure for this questions is:             [Verb to be + Subject + not + Complement + ?]

   Examples:          
                                     “Am I not free?”
                                     “Am I not a brother and a man” – Anti-slavery medallion (1787)
                                     “Look at the birds of the air …“Are you not much more valuable than they?”                                                                                                                                      – Matthew 6:26-28 (NIV)
                                     “Is she not amiable?, Is she not lovely?” – Charles H. Spurgeon
                                       (= “Formal”, “poetical”, unusual in nowadays- conversations in the U.S.)

3. Expressions like “Isn’t it..?”, “Isn’t he…?” or “Aren’t you…?” are very common in everyday usage in the United States or Canada. Though there is a debate, some people consider these expressions acceptable for Standard English, as they are conventional in everyday-conversations, and they’re widely used in informal contexts. However, they must be contractions, because the questions “are not I..?”, “is not he…?” or “are not you…?” are considered incorrect in current Contemporary English.

Examples:            “Isn't she lovely?, Isn't she wonderful?, Isn't she precious…?” – Steve Wonder

             (= “Informal”, “conversational”, very common nowadays in the U.S.)

4. Although it’s grammatically incorrect to use “I” with “are”, there is an exception. Many people, especially in the United States, use the expression “aren’t I…?” for interrogative questions with verb to be, or for question tags. Nowadays, “aren’t I..?” may be considered pragmatically correct, and you could even find it in books.

Conclusion

After all, what is important to notice is that the usage of these different elements may vary depending on the context (the place where you’d use it), the appropiacy (informal /formal) you want to give, or the register of the language.