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Articles in English are used to make a noun more specific. The most used articles are [a], [an], and [the], and introduce a noun. As such, they come before a noun. Articles are classified as indefinite or general and use [a, an] or definite specific and use [the]. Indefinite articles [a, an] are used with non-count nouns.
When to use a, an or the
It depends on the noun you want to use and:
whether it is a count or non-count noun
if the noun is singular or plural
Articles are Used with Count Nouns
Count nouns are things you can divide into separate pieces or perceive as being true:
a finger the finger(s)
a table the table(s)
a doctor the doctor(s)
a dollar the dollar(s)
an apple the apples(s)
To make a general statement about a single count noun, use [a] or [an] before the noun.
1. A noun that begins with a consonant is preceded by [a]: a day, a sunrise, a walk
2. A noun that begins with a vowel is preceded by [an]: an apple, an egg, an idea