There are 9 parts of speech or word classes in English language:
– nouns
– pronouns
– determiners
– verbs
– prepositions
– adjectives
– adverbs
– conjunctions
– interjections

Nouns are a group of words that we use to name:
– people: man, woman, teacher, John, Mary
– animals: cat, rabbit, horse, elephant
– plants: palm tree, coconut trees, grass, wheat, corn
– places: home, office, town, village, England
– concrete objects: chair, table, ball, water, money, sugar
– abstract objects: truth, lies, happiness, sorrow, time, friendship

Determiners, prepositions and adjectives are related to the use of nouns.

– Determiners specify a limit to nouns.
I saw a cat.
‘A’ is a determiner.
‘Cat’ is a noun.

– Prepositions specify relations between two nouns.
The cat is under the bed.
‘Under’ is a preposition.
‘The cat’ and ‘the bed’ are nouns.

– Adjectives specify the condition, characteristic, emotion of nouns.
James is sick.
‘James’ is a noun.
‘Sick’ is an adjective.

James is happy.
‘Happy’ is an adjective.

We use determiners in front of nouns or noun phrases.
a cat
the cat
that person
two American citizens
all books
some information

A, an, and the are part of determiners and usually called ‘articles.’
– a, an: indefinite articles
– the: definite article

A/an in front a noun specifies that the noun is not known specifically.

Do you have a car?
‘A car’ refers to something in general, not a specific car.
We do not know which car or which type of car that is being discussed.

I live in an apartment.
We do not know which apartment that the speaker or writer is talking about (not specific).

The in front of a noun specifies that the noun is known specifically.

Where did you park the car?
The speaker and listener know exactly which car they are talking about (the car that they drove).

We had to paint the apartment before we sold it.
The speaker and listener know exactly which apartment they are talking about.

The makes a noun definite or specific.

Have you been to a circus show?
A circus refers to any circus show, not a specific circus.

Have you been to the circus show?
The circus refers to one specific circus show, maybe a circus show that is playing in that town.

Would you like an apple?
An apple is not specific. We do not know which apple the speaker is talking about.

Did you see the apple that I just brought?
The apple is specific. We know which apple the speaker is talking about (the one that he/she just brought).

If we are talking about something for the first time (in writing or in speech), we use ‘a/an’ first.
After we specify the noun, we can use ‘the’.

I saw a man. -> First, we use a/an.
The man wore a black hat. ->Then, we use the.
The man refers to the one that the speaker saw (specific).

I bought a book last week. -> First, we use a/an.
The book was very good. ->Then, we use the.
The book refers to the book that the speaker bought last week (specific).

A/an can only be used with singular countable nouns.
– I have a sister.
– Give me an egg.

A/an CANNOT be used with plural countable nouns.
I have a sisters. (wrong)
I have two sisters. (correct)
Give me an eggs. (wrong)
Give me three eggs. (correct)

The can be used with:
– singular countable nouns
– plural countable nouns

The lion roared. (correct)
The lions roared. (correct)

The tree fell. (correct)
The trees fell. (correct)

A/an CANNOT be used with uncountable nouns.

Could I have rice with my fish? (correct)
Could I have a rice with my fish? (wrong)

I hope we have nice weather. (correct)
I hope we have a nice weather. (wrong)

The can be used with uncountable nouns when we are referring to something specific.

The rice we bought yesterday is better than the one we bought last week.
We know exactly which rice that the speaker is talking about (the one that they bought yesterday – specific).

The weather was awful this morning.
We know exactly which weather that the speaker is talking about (this morning’s weather).

A/an can be used with uncountable nouns as long as there are quantity expressions in the form or countable nouns.

I just had a glass of milk.
Milk is an uncountable noun.
Glass is a countable noun and can be used a quantity expression.

She gave me a piece of advice.
Advice is an uncountable noun
Piece is a countable noun and can be used a quantity expression.

A is used in front of nouns that start with a consonant:
– a book
– a car
– a teacher

A is used in front of nouns that start with a vocal but having a consonant sound:
– a university (read as you-nee-ver-see-tee)
– a united grup (read as you-nai-ted)
– a one-year-old child (read as wan)

An is used in front of nouns that start with a vocal:
– an apple
– an umbrella
– an orchestra
– an old shoe

An is used in front of nouns that start with a consonant but having a vocal sound:
– an hour (“h” is silent, read as en-auer)
– an MP3 player(M is read “em” – has “e” vocal sound, read as en em-pee-tree )

A/an and the CANNOT be used if there is already another determiner in front of the noun.

I love my job. (correct)
I love the my job. (wrong)
I love a my job. (wrong)

Do you want this book? (correct)
Do you want the this book? (wrong)
Do you want a this book? (wrong)

A/an is usually used to describe a profession.
– John is a driver.
– Jane is a teacher.

The can be used with profession if it refers to specific person or people.
– Tom is talking to the taxi driver. (The driver is specific.)
– Ms. Thompson is talking to the teachers. (The teachers are specific.)

The is used when talking about inventions, musical instruments, cultural institutions in general.
– The computer must be the greatest invention ever.
– The violin sounds different to the viola.
– I love a night at the opera.

The is also used for things that are universally known.
– The earth moves around the sun.
– I love watching the moon at night.
– We lay on the grass and watched the stars.

The is used when talking about things that are part of everyday life.
In this context, “the” does not refer to something specific.

– I don’t buy the newspaper these days.
– I read it from the Internet.
– They always take the train.

We use the for:
– mountains: the Alps, the Eiger
– islands: the West Indies
– rivers: the Danube
– desert: the Gobi Desert
– seas or oceans: the Black Sea
– geographical areas or habitats: the Amazon rainforest
– highways: the 166 Highway
– names of some countries: the People’s Republic of China, the Philippines

The is used when talking about specific groups in society.
– I think we as citizens need to help the poor.
– The rich should pay more tax.
– The young need to support the society.