A vs An

—> ‘A’ and ‘an,’ along with ‘the,’ are articles. Their purpose is to help define a noun. They may come directly before a noun or, if there are adjectives before the noun, they will come before those adjectives.
Examples: A clock. An idea.
Example: ‘A big clock’ NOT ‘big a clock.’
Example: ‘A good idea’ NOT ‘good an idea.’

—> ‘A’ is most commonly used before nouns or adjectives that begin with a consonant (any letter that is not a vowel).
Examples: A clock. A time. A dog.
Example: A pertinent question. A brave act.
Clarification: The adjectives ‘pertinent’ and ‘brave’ begin with a consonant, so ‘a’ is used. If there are adjectives, it does not matter what the noun begins with; it only matters what the word ‘a’ or ‘an’ comes before begins with.

—> ‘An’ is most commonly used before nouns or adjectives that begin with a vowel (a, e, i, o, u, sometimes y).
Examples: An egg. An announcement. An act.
Examples: An exciting thought. An overbearing act.
Clarification: The adjectives ‘exciting’ and ‘overbearing’ begin with a vowel, so ‘an’ is used. If there are adjectives, it does not matter what the noun begins with; it only matters what the word ‘a’ or ‘an’ comes before begins with.

—> However, it is not always as simple as consonant vs vowel. There are cases where ‘an’ comes before a word that begins with a consonant and ‘a’ comes before a word that begins with a vowel.’
Example: An honor.
Clarification: ‘H’ is a consonant, but it is not pronounced in the word ‘honor.’ Since the consonant is silent and the next heard letter is a vowel, ‘an’ is used.
Example: An x-ray.
Clarification: ‘X’ is a consonant, but it is pronounced with a vowel sound: ‘ex-ray.’ Since the first letter sounds like a vowel, ‘an’ is used.
Example: A university.
Clarification: ‘U’ is a vowel, but it is pronounced with a consonant sound: ‘yoo-niverstiy.’ Since the first letter sounds like a consonant, ‘a’ is used.

—>Paying attention to the sound of the first letter is how to determine if words that begin with ‘y’ are using ‘y’ as a vowel or a consonant. Fortunately, most words that begin with ‘y’ do use ‘y’ as a consonant.
Example: A yard.
Clarification: ‘A’ is used because the ‘y’ in yard uses the ‘yuh’ sound which is a consonant sound.
Example: An yttrium atom.
Clarification: ‘An’ is used because the ‘y’ in yttrium uses the short ‘i’ sound (itt-rium) which is a vowel sound.