Use “a” before singular, countable nouns when the noun is mentioned for the first time or is nonspecific
Use “an” before singular, countable nouns that begin with a vowel sound
Use “the” for specific nouns already known to the speaker and listener
Use “the” for unique things such as the sun, the moon, and the Earth
Use “the” with superlatives and ordinal numbers
Use “the” with names of rivers, oceans, seas, mountain ranges, and groups of islands
Use “the” with countries or places that include words like kingdom, states, republic, or union
Use “a” or “an” with professions and roles
Use no article with plural nouns and uncountable nouns when speaking generally
Use no article with most proper nouns, such as names of people, cities, and countries
Use no article with meals, languages, and academic subjects in general
Use no article with fixed expressions like at home, by car, and in bed