Here's why:
* "Decide" is a verb: It means to make a choice or form an opinion.
* Adjectives describe nouns: They tell us more about the thing or person being discussed.
While you can't directly use "decide" as an adjective, there are ways to express the same idea:
* "Decisive" is an adjective that means "characterized by or showing firmness of purpose or resolution" or "having a clear and definite effect or result." It can be used to describe a person, a decision, or an action.
* "Decided" can be used as an adjective to mean "firmly determined." For example, you might say "She had a decided opinion on the matter."
* "Deciding" can sometimes be used as a participial adjective. For example, "The deciding factor in their choice was the price."
Example:
Instead of saying "The *decide* factor," you could say:
* "The decisive factor"
* "The deciding factor"
Important Note: While "decide" isn't an adjective, it can be part of a compound adjective, like "decision-making."