used to talk about something already known or mentioned
The cat I saw yesterday was black.
used for the only or main one of its kind
The sun is very bright today.
used to specify which person or thing you mean
The book on the table is mine.
used to talk about something in general, not a specific one
The piano is a beautiful instrument.
used with adjectives to refer to a group of people or things
We should help the poor.
used before a family name to refer to the whole family
The Smiths are coming to dinner.
used with units to mean 'every'
She gets paid by the hour.
enough of something for a purpose
I don't have the time to help you.
used with time to mean 'the present'
This is the song of the day.
used to show that something is famous or important
She met the president of the company.