To talk about a particular person or thing
The definite article the is used to talk about a particular person or thing.
- The book you want is out of print. (Which book? The one you want.)
- Let’s go to the park. (Which park? May be the one in the town.)
The definite article the is also used to talk about a person or thing that has already been referred to.
- I saw a girl in the park. The girl was crying. (Which girl? The one I saw in the park.)
Before a singular noun meant to represent the whole class
When a singular noun is meant to represent a whole class to which it belongs, it is used with the definite article the.
- The cow is a useful animal. (Here the singular noun cow represents a whole class.)
- The rose is the sweetest of all flowers.
- The spider has eight legs.
Note that these sentences can also be written using a plural noun without any article.
- Cows are useful animals.
- Roses are the sweetest of all flowers.
- Spiders have eight legs.
Before the names of certain books
Examples are: The Vedas, The Illiad
Before superlative adjectives
The definite article the is used before superlative adjectives.
- She is the best person I have seen.
- Which is the highest mountain in the world?
Before ordinal numbers
- Who was the first woman to win a Nobel Prize?
- The first half of the film is more interesting than the second half.
Before musical instruments
- He can play the flute.
As an adverb with comparatives
- The more the merrier.
- The more they get, the more they want.
- The higher you climb, the cooler it gets.