There are a couple of interesting questions which were asked in connection with the rules. If you have been taught simply to use «a», «an» with countable nouns and «the» with uncountable nouns, please forget everything you have learnt. We shall begin from the beginning!
Once upon a time, there was a house. In the house lived a man. The man had a daughter.
a house — the house a man — the man
The first time something is mentioned, it is general — it is just a house or a man; it is one of many. When you refer to it subsequently, it is unique. You are talking of one house or one man specifically. It becomes the house and the man.
A dog is in my garden. THE dog is brown. I need to buy A new car. THE car I buy must be economical.
If something is general, it is A. If it is unique or specified, it is THE. A noun or nouns can be unique or specific by association; for example:
A car hit a tree. THE driver of THE car was drunk.
In the first sentence, both car and tree are introduced, therefore A car, A tree. In the second sentence, THE car because it has already been introduced, but notice also it is THE driver. Although he has not been mentioned before, a car can have only one driver. He is unique by association!
If we know that A, AN are used for general nouns and THE for unique nouns, we can understand:
She is A politician, but She is THE Queen.
I would like to swim in AN ocean, but I would like to swim in THE Pacific Ocean. It is A biscuit, but It is THE biscuit I am eating.
Please note that some proper nouns do not take an article:
Mount Vesuvius, Mount Everest, Skull Island.
I am going to climb THE mountain, but I am going to climb Mount Everest.
Also countries and place names unless their title includes an article: Russia, Ukraine, but The Seychelles.
I am going to visit Russia, but I am going to visit THE Seychelles.
General plural nouns don’t have an article:
I like driving THE car, but I like driving cars.
There is A field to cross before you reach your house. There are fields to cross before you reach your house.
Adjectival ordinal numbers. When using these, they require the definite article:
THE first book I read. She lives in THE second house on the right. My Birthday is on THE third of November.
Comparatives and superlatives. Better, bigger, sweeter
Best, biggest, sweetest — there can be only one best, biggest, sweetest so it is unique. therefore: THE best hotel, THE biggest garden, THE sweetest apple.
Remember always that every rule has exceptions. I have done my best here to simplify the rules for you. I hope it is useful! Finally, what many people believe to be the only rule but it is about countable and uncountable nouns, not articles. I add it only for interest:
Beer is bad for your health. Cigarettes are bad for your health.
The rule we have established:
1. Singular nouns require an article, plural nouns don’t. I like A rose; I like THE rose; but, I like roses.
I am going to A shop; I am going to THE shop; now note — I am going to THE shops. .
I am going to A school; I am going to THE school; you use these in the singular if you are simply visiting a school, but if you are a pupil or a teacher who goes every day: I am going to school; note there is no article in the singular here!
I hear an anguished cry from you, «What about — I am going to work?» This is different because «to work» is the verb. We know this because you cannot say, «I am going to THE work»!
Children, however, correctly say, «I am going to school.» To school is NOT the verb here, unless children now go not to learn, but to teach!
Another interesting exception: the verb To play!
I play guitar. Oh, do you? I play trumpet.
Let’s play tennis! The children are playing hopscotch.
An article is not used for sports, children’s games, and pastimes such as chess and Monopoly. With musical instruments it is possible to add an article, but it is not necessary; therefore I suggest it is easier for you to use all nouns which are objects of the verb to play without an article.