1. The indefinite article a / an!
If a noun begins with a vowel sound we use the indifinite article an. If it begins with a consonant sound we use a. It is the sound which is important, not the spelling.
An apple, an elephant, an honest man, a hobby, an uncle, a university.
The indefinite article is most often used:
a. when we mention a countable noun for the first time.
Yesterday a policeman wanted to ask me some questions.
I think I’ve broken a tooth.
b. when we want to classify things/people or say what they are like.
He is a very talented actor.
Platinum is a valuable metal.
c. to name a person’s job.
Maria is a doctor.
d. before certain numbers and in certain “number expression”
She is going to pay a hundred/ a thousand / a million pounds for it.
He was driving at sixty miles an hour.
I work forty hours a week.
2. The definite article the.
The definite article is most often used:
a. When we refer to something that has been mentioned already.
To make a Spanish omelette, take three eggs and a large potato.
Cut the potato into small cubes and …
b. when we mention something that the listener knows about or something that has already been defined. By the way, I went to see the film you recommended.
c. when there is only one (often in a particular context).
The sky is rather grey today.
Can I speak to the headmaster, please?
The view from this window is really lovely.
d. with superlatives.
She is the best teacher at our school – we are the naughtiest students!
e. with musical instruments.
I play the piano and my sister plays the violin
f. with means of transport.
I think we should take the bus to Athens, rather than the train.
g. with inventions.
The computer has dramatically changed the way we live and work.
h. with species of animal in the singular.
The brown bear has almost disappeared in certain parts of the world.
i. when we use an adjective (as a noun) to classify or to describe a group of people.
Winter is particularly difficult for the old and the sick.