The English indefinite article is a [ə] before most words; a lion, a peanut, a map, a unicorn, etc., but it is an [æn] before words like apple, onion, icicle, evening, eagle, and honor. To what natural classes of sounds do the sounds at the beginning of each set of words belong? (That is, before what class of sounds do you use [ə]? [æn]?]

We use a [ə] before words that when we pronounce them, the sound is the one of a consonant, and we use an [æn] before words that when we pronounce them, the sound is the one of a vowel.

Explanation:

A [ə] is used before words that when we pronounce them, they start with a consonant, for example, a house, a cat, or a peanut.

On the other hand, an [æn] is used before words that when we pronounce them, they start with a vowel, for example, an onion, an orange, or an elephant.

Even though the word honor does not start with a vowel in its spelling when we pronounce it, it does, that is why these words use the definite article an. Another example of this is university or unicorn, they are spelled with a vowel at the beginning, but when we pronounce them, we pronounce a consonant [j].