English uses the indefinite articles 'a' and 'an' based on the sound (not spelling) of the following word's first phoneme. The author analyzed 32,455 words and found that only 129 required exceptions to the vowel-sound rule, such as 'an hour' and 'a unicorn'.
An analysis of the English indefinite articles 'a' and 'an' reveals that the correct choice depends on spoken sound rather than written letter. Of 32,455 words examined, only 129 required exceptions to the vowel-sound rule, such as 'unicorn' (consonant sound despite vowel letter) and 'hour' (vowel sound despite consonant letter).