Comment Articles for vowel sounds (Score 1) 174
It's not technically if the letter is a vowel, it's the vowel sound.
The word "union" actually starts with the sharp Y sound, which is a consonant sound. It gets the article "a".
The word "onion" starts with the "uh" sound, which is a vowel sound. It gets the article "an".
The goal is to prevent two vowel sounds from touching between words. "a apple", "a orange", "a eagle" feels super weird to most native English speakers.