Is " I'm a idiot" grammatically correct?

Question

or is it "I'm AN idiot"

when do you use 'a' or 'an'?

Answer 1

an because you use an if the next word begins with a vowel

Answer 2

Generally the rules that you use "a" before words that begin with consonants and "an" before words that begin with vowels. However, most of the time the usage is determined by the pronunciation of the following word.

For example:

An hour ("hour" begins with a vowel sound)

A history ("history" begins with a consonant sound)

Also you would say “a union” even if union because the pronunciation begins with “yu”, which is a consonant sound.

Answer 3

You need to use "an" before the vowel "i" in "idiot".

Answer 4

No, it is not grammatically correct. The correct grammar is "I'm an idiot". You use "an" before a word that starts with a vowel. An exception is "hour". For example: I will meet you in an hour.  

Answer 5

"I'm an idiot."

The indefinite article "an" precedes a word with an opening vowel sound.

The indefinite article "a" precedes a word with an opening consonant sound.

Answer 6

AN.

Use "an" when the next word starts with a vowel.

Use "a" when the next word starts with a consonant.

I'm a fool.  I'm an idiot.