Using a or an. (indefinite articles) with singular count nouns. Use a before a consonant sound (a car) and an before a vowel sound (an uncle). Consider sound rather than spelling: a house, an hour.

A or an tells readers they do not have enough information to identify specifically what the noun refers to. Compare these sentences:

I need a new coat for the winter.

I saw a coat that I liked at Dayton’s, but it wasn’t heavy enough.

The coat in the first sentence is hypothetical rather than actual. Since it is indefinite to the writer and the reader, it is used with a, not the. The second sentence refers to an actual coat, but since the writer cannot expect the reader to know which one, it is used with a rather than the.

If you want to speak of an indefinite quantity rather than just one indefinite thing, use some or any with a noncount noun or a plural count noun. Use any in negative sentences.

This stew needs some more salt.

I saw some plates that I liked at Gump’s.

This stew doesn’t need any more salt.