Why do we learn count and non count nouns together with article usage? This is an important grammar concept for “subject – verb agreement.”

If you do not understand if a noun is countable or uncountable, you cannot make a good decision about which article to use – a, the, or nothing.

If you do not know whether your subject is singular or plural, you cannot choose the right form of the verb. Therefore, you risk having your whole sentence be wrong.

Your hair looks really beautiful today.

NOT,
Your hairs look really beautiful today.

DEFINITION Countable nouns

Count or countable nouns may be singular or plural because if you can have one of something, you can also have many of that same thing. You can have one dog or you can have many dogs.

Singular count nouns

A = One
use “a/an” to mean one, or an example of one. A dog = an example of a dog, one dog.
use “the” to refer to a specific person, place, or thing. The dog = the reader/listener knows which dog you mean – your dog, the dog with the fluffy tail.

Plural count nouns
NEVER use a/an with a plural noun. A = one. You cannot have one of something plural. You CANNOT write or say a dogs!!
it is fine to use a number (10, 100, 1000) or use quantity words – a lot, a few, some, many + dogs.
use the article “the” to describe a specific group of plural count nouns. The dogs = The reader/listener knows which dogs you mean – your dogs, your parents dogs, the French bulldogs I get paid to take for a walk.
Use no article at all when you are speaking in general about plural, countable nouns.

 French bulldogs are really sweet.

Examples:
A teacher left his or her tablet in the classroom. (A teacher = one teacher did it, but we don’t know which one.)
The teacher left her laptop in the classroom. (The English teacher left it there; we know which specific teacher did it.)
The teachers are making our lives difficult this semester.
Teachers are the most underpaid professionals in the world.

DEFINITION Uncountable nouns

Non count/uncountable nouns are ALWAYS either abstract, in tiny parts, or impossible to quantify.
Do NOT use the article “a/an” with non count nouns. You cannot use the article “a/an” with liquids or powders unless they are in containers. You CANNOT write or say “a water,” but it is correct to describe a bottle of water, the bottle of water, or the bottles of water.
You may use quantity words – a lot, a little, some.
Some nouns that are countable in Italian are non count in English: advice, information, jewelry, hair, garbage, fish, furniture, etc. 

For example, you CANNOT write or say advices in English. It does NOT exist! Therefore, it is WRONG to write or say an advice. You may say or write – a piece of advice or a lot of advice.

It is good to memorize the categories of uncountable nouns: school subjects (biology, history), powders (salt, cocaine), liquids (water, wine), abstract ideas or feelings (joy, pain), collective nouns (furniture, jewelry), minerals (gold, silver) and certain foods (cheese, bread, fish).

Examples:

The joy I feel on my vacation is very intense. (specific)

Otherwise, no article:
Joy is the feeling I have when I am with you.
Biology is an interesting field of study.
I love every type of bread.
My family’s store sells furniture; we sell chairs, tables, sofas, desks, and everything for the home. (The different types of furniture are countable!)