The rules for using either a or an before adjectives are 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)
