According to the website dicionário Cambridge, demonstratives are word that show or point at something.
Demonstratives: are determiners that points to a noun in particular ( an object, a person, an event ). There are four demonstratives to describe distance and number.
This & These: short distances
This and These point to near objects.
This is used before singular nouns:
- This computer is modern.
- This party is awesome.
- This pie is delicious.
- What is this?
These is used before plural nouns:
- These girls is are the best.
- These fruits are fresh.
- These houses are wonderful.
- Are those clothes clean?
That & Those: long distances
We use That and Those to point or show something far from us.
That is used before singular nouns:
- That ship is white.
- That tall bay is Ana’s brother.
- That man is my new teacher.
- Who is that?
Those is used before plural nouns:
- Those glasses are new.
- Those people over there are my friends.
- Those pictures are expensive.
Past X Present
When we talk about actions in a near period of time we use: This and These:
- This is the best time of my life.
- These days are really hot.
- This year is good.
If the action is in the past we use That and Those:
- That night was great.
- Those years were great.
- Those times are over.
We use demonstrative to introduce people
- This is Sandra.
- This is my sister Camilla.
- This is my boss, Hector.
- These are my friends. This is Susan and this is Brian.
Expressions with demonstratives
- This is it!
- That’s it!
- Tha’s all!
