Why is it an hour not a hour?
You should say, ‘an hour’ (because hour begins with a vowel sound) and ‘a history’ (because history begins with a consonant sound). You should say ‘a union’ even if union begins with a ‘u’. This is because the pronunciation begins with ‘yu’, a consonant sound.
What is correct a hour or an hour?
For those words that are written with the first letter as a consonant, but which are pronounced with the first letter as a vowel, such as “hour” and “herb,” the correct way to present them in a written document (e.g. your scientific manuscript written in American English) is: “An hour” and “An herb.”
Do you use a or before unicorn?
Unicorn doesn’t follow the pattern because, when you say it, it doesn’t start with a vowel. It starts with a consonant. The sound “yu” is a consonant, so we say, “a unicorn.” The word unicorn is an example where a word is spelled with an initial vowel but is pronounced with an initial consonant.