They are formed from proper nouns.
Thanksgiving -dinner-
Proper Adjectives
This That These Those
Adjective: This drawing is made of chalk⬅️⬅️⬅️⬅️need to have a noun
Pronoun: Those are falling down the stairs⬅️⬅️⬅️⬅️doesn’t have a noun
Demonstrative Adjectives
Are also adjectives
Articles
They refer to any general member of a group
A, An
Indefinite articles
Refers to someone or something in particular
The
Definite Articles
Is a word used to modify a noun or a pronoun
It may answer to the questions:
What kind? Which one? How many? How much?
Adjective