The indefinite article

 The definite article is the word the. It limits the meaning of a noun to one particular thing. For example, your friend might ask, “Are you going to the party this weekend?” The definite article tells you that your friend is referring to a specific party that both of you know about. The definite article can be used with singular, plural, or uncountable nouns. Below are some examples of the definite article the used in context:

Please give me the hammer.

Please give me the red hammer; the blue one is too small.

Please give me the nail.

Please give me the large nail; it’s the only one strong enough to hold this painting.

Please give me the hammer and the nail.

The indefinite article takes two forms. It’s the word a when it precedes a word that begins with a consonant. It’s the word an when it precedes a word that begins with a vowel. The indefinite article indicates that a noun refers to a general idea rather than a particular thing. For example, you might ask your friend, “Should I bring a gift to the party?” Your friend will understand that you are not asking about a specific type of gift or a specific item. “I am going to bring an apple pie,” your friend tells you. Again, the indefinite article indicates that she is not talking about a specific apple pie. Your friend probably doesn’t even have any pie yet. The indefinite article only appears with singular nouns. Consider the following examples of indefinite articles used in context:

Please hand me a book; any book will do.

Please hand me an autobiography; any autobiography will do.

Exceptions: choosing a or an

There are a few exceptions to the general rule of using a before words that start with consonants and an before words that begin with vowels. The first letter of the word honor, for example, is a consonant, but it’s unpronounced. In spite of its spelling, the word honor begins with a vowel sound. Therefore, we use an. Consider the example sentence below for an illustration of this concept.

My mother is a honest woman.

My mother is an honest woman.

Similarly, when the first letter of a word is a vowel but is pronounced with a consonant sound, use a, as in the sample sentence below:

She is an United States senator.

She is a United States senator.

This holds true with acronyms and initialisms, too: an LCD display, a UK-based company, an HR department, a URL.