The rule for using either a or an before adjectives + nouns is the same as before nouns. An should be used before adjectives that begin with a vowel sound (a, e, i, o, u).
- an apple
(vowel sound/a-pel) - a red apple
(no vowel sound/reh-d) - an improvement
(vowel sound/im-pru-v-ment) - a massive improvement
(no vowel sound/mah-seh-f) - a gentleman
(no vowel sound/gen-til-man) - an honourable gentleman
(silent h/vowel sound/on-er-rable)
