The article. Part 1

CN Singular
We use the zero article before a MN in the generic meaning
We use the indefinite article if a CN Singular is a predicative

I have a car
The car I have is green
I love ⊗ music
I am a teacher
Leonardo is a genius

is modified by a LIMITING/ PARTICULARIZING attribute
We use the indefinite/zero article if a noun is modified by a DESCRIPTIVE attribute

The story I told you yesterday did not have a single word of truth
Yesterday he told me an absolutely unbelievable story
⊗Unbelievable stories may be true sometimes
⊗Good food is expensive

a consonant sound
a man
a red apple
a university
a helmet
a historical event

An
is used before a word beginning with a vowel sound
an apple
an old man
an uncle
an heir

some new information (thus becoming the focus of communication or the “rheme” of the sentence)
It names and classifies the object, denoting, what kind of object (thing/ person) the speaker has to deal with

A pretty girl of about eight entered the room
John has brought me a book that he believes I should start reading right now
They saw a house with a smooth lawn in front of it
His wife, a woman of uncertain age, was also present at the ceremony

object (thing/ person/ amount)
It may be unique or the situation may make it specific, but it is hardly the focus of communication (the”theme” of the statement)

Let’s close the window, I am afraid of catching a cold.
The sun rises at 8 a.m.
The water in the bathtub is tepid, you will be frozen
Has anyone fed the dogs?

group of objects, to give some additional information about them
She wore a large straw hat of native make
There was a wonderful concert at the Victoria Hall we could have gone to

Particularizing /Limiting (the)

is used to point out a particular object (person/thing/amount) or a number of objects as distinct from all other objects of the same class/kind
-Which hat are you going to wear?
-The large straw one, it matches my dress best.

child? (descriptive)
Ordinal numbers:

the most irritating person/ the best friend/the biggest hit
the same/ only/ very/main/principal/ left/right/wrong/ central/ following/ present/ former/ latter/ last/ next etc.
The first celebrity/ the forth room down the corridor

London
The isle of Man
The lake of Ontario
The cover of a/the book
The roof of a/the house
The figure of a/the man
The singing of birds
The shot of a gun
The sound of her voice