We use a / an with a singular noun when we talk about something for the first time . We use the with a singular or plural noun when we talk about something for the second time:
- There´s a shirt here and a sweater. The sweater´s Rob´s and the shirt´s mine.
- Here are my shirts and sweaters. The shirts are clean but the sweaters are dirty.
- She works in a shop in London.
- I live near the post office.
- talk about a person´s job: Jenny´s a teacher.
- describe something or someone with the verb be: That´s a good book.
We use the with:
- musical instrumets: Rob plays the piano.
- the names of cinemas, theatres, museums and hotels:
the Picturehouse, the Globe Theatre, the British Museum, the Hilton Hotel
We do not use a / an / the with:
- sports and games: We sometimes play football.
- school subjects: I like Biology.
- meals: When´s dinner?
- the names of streets: Baker Street
- the names of countries, cities and towns: Japan, Rome, Cambridge
For more information about "Indefinite articles" watch the video below.