From Flickr Creative Commons (Credit: http://farmanac.com/)

“The,” “a,” and “an” are called articles in English.  Many student writers are aware that “the” is specific (or “definite”) while “a” and “an” are both non-specific (or “indefinite”).  For example:

She ate a hot pepper. (indefinite: any hot pepper.)

She ate the hot pepper. (definite: the reciever knows the hot pepper she ate or perhaps there was only one)

The “indefinite” an is used before a word that begins with a vowel:

She at an orange-colored hot pepper.

Plurals: no article is used with indefinite articles whereas an article is used with the definite article.

She ate hot peppers every morning. (indefinite)

The hot peppers she ate every morning contributed to her ulcers. (definite)

Non-count Nouns: no article is used with indefinite articles; an article is used with the definite article.

Spicy food is hard to avoid in our globally-influenced cuisine.

The spicy food on the menu reflects the influence of the Indian population in our neighborhood.

Need more? Visit the Purdue Online Writing Lab regarding this issue.