English uses a and an before singular countable nouns when the noun is one thing and not specific. They help introduce a person, animal, place, or thing. They are part of the noun phrase.

Use a before a consonant sound. Use an before a vowel sound. The choice depends on sound, not only on the first letter.

Some words begin with a vowel letter but a consonant sound, so they use a. Some words begin with a consonant letter but a vowel sound, so they use an. In some names, titles, and fixed expressions, usage can vary by style or dialect, but the sound rule is the main rule.

Word	Notation	Description
a university	yoo	It begins with a consonant sound, so it takes a.
a European	yoo	It begins with a consonant sound, so it takes a.
an hour	our	It begins with a vowel sound, so it takes an.
an honest person	on	It begins with a vowel sound, so it takes an.

Use a or an before a singular job, role, or identity word. This use describes what a person is. It is common after be.

Use a and an only with singular countable nouns. Countable nouns can be one item, two items, or more. The indefinite article is for one item.

You can now use a and an before singular countable nouns in English. You can choose the article from the first sound of the next word. You can also use indefinite articles with jobs and descriptions, and you know they are not used with plural or uncountable nouns.