Indefinite Articles -

The words "a", "an", and "the" are special adjectives called articles. Articles define nouns as either specific or unspecific. "A" and "an" are indefinite articles. Indefinite articles are used before singular nouns and countable nouns that are not specified. You cannot use "a" or "an" before plural nouns or uncountable nouns.

"A" is used before nouns starting with consonants letters (letters other than a, e, i, o, u). "A" is also used with words that sound like they start with a consonant even if they start with a vowel (university, unit, one). "An" is used before nouns starting with vowels (a, e, i, o, u) or with a silent h (hour, honor).

Indefinite Articles - singular nouns

Consonants letters (letters other than a, e, i, o, u)	Vowels (a, e, i, o, u)
A banana A car A helicopter A lamp A woman A man A dog A tree A sandwich A robot A university A unit	An apple An animal An egg An elephant An igloo An ice cream cone An ostrich An onion An umbrella An ugly sweater An hour An honor