These and those are plural forms of this and that. We use them to identify the things or people we are talking about. ‘These’ is used for persons or things nearby and ‘those’ is for persons or things at a distance. They are both demonstrative pronouns and demonstrative adjectives.
Demonstrative pronoun is used as a substitute for the noun or noun phrases and they can only be used for objects and not for people.
Example:
Those people are waiting. ( NOT: Those are waiting.)
These girls are pretty. ( NOT: These are pretty.)
Proper use of ‘these’ and ‘those’ as demonstrative pronouns:
I am eating pastries now and they are delicious.
These are delicious.
The cars I saw on TV are expensive.
Those are expensive.
The stars in the sky are too bright.
Those are too bright.
Demonstrative adjectives are found before the noun. They are used to describe or modify the nouns.
Examples:
These clothes are old.
These pencils are mine.
Do you want to buy these flowers?
Those houses are on sale.
Those bags are stylish.
Are those seats taken?