When this and that are used to modify nouns they treated as what rather then pronouns?

When "this" and "that" are used to modify nouns, they are treated as demonstrative adjectives rather than pronouns.

Here's why:

* Pronouns replace nouns, while adjectives modify nouns.

* Demonstrative adjectives point out specific nouns, and "this" and "that" fulfill this role.

Examples:

* Pronoun: "This is my favorite book." (Here, "this" replaces the noun "book".)

* Demonstrative adjective: "This book is my favorite." (Here, "this" modifies the noun "book" by specifying which one.)

Similarly, "that" can be used as a pronoun or a demonstrative adjective:

* Pronoun: "That is my cat." (Here, "that" replaces the noun "cat".)

* Demonstrative adjective: "That cat is mine." (Here, "that" modifies the noun "cat" by pointing out which one.)

Therefore, when "this" and "that" are used to describe a specific noun, they act as demonstrative adjectives, modifying the noun rather than replacing it.