Demonstrative: What is a Demonstrative Determiner? Demonstrative Determiners with exercises: Use of THIS THAT THESE THOSE

THIS
THIS points out the things, persons or
ideas that are very close to us.

Example- This marker is mine.
(Means – The marker is very close to the person who is pointing it out.)
This book is not yours.
(Means the book  is very close to the

 person who is pointing out.)
This idea is better than that one.
( This idea – the idea that is going on in the mind  right now.)
Were you asking about this boy?
(Means the boy is very close to the speaker.)

In precise, we can notice that we are talking about the things
or ideas that are very close to us.

THAT

That talks about the things, persons, or ideas that are very far from us.

Example
That book is not mine.
(Means- The book is very far from the person who is pointing it out.)

That idea didn’t really work.
(Means- The idea is in the distant memory of the speaker)
My bag is better than that of yours.
(Means- The bag is very far from the person who is pointing it out.)
Your book is heavier than that of mine
(Means- The book is far from the speaker)

So we can simply say that the person, things, or ideas
that have been mentioned in the above sentences
are either far from the speaker or in his distant memories.

THESE-

Plural of This

‘These’ actually  talk s about many persons, things, or ideas that
are very close to us.
Example

These grapes are very sour. I can’t eat them.
Where are you these days?
Can you suggest to me some more plans than these?

THOSE-

Plural of That

That talks about many things,  persons,  things or ideas that area a 
little or very far from the speaker.

Example

Those clocks never give the correct time.
These plants are bigger than those.
Those ideas just really didn’t work.

So these are some usage of demonstratives.