Here's why:
* Antecedent: An antecedent is the word or phrase that a pronoun refers to. For example, in the sentence "The dog wagged its tail," "dog" is the antecedent of the pronoun "its."
* "Before" is a preposition. It indicates time or position in relation to something else. It doesn't function as a noun or pronoun that would require a pronoun to refer back to it.
Example:
* "The dog walked before its owner."
* "Before" is a preposition indicating time.
* "Dog" is the antecedent of the pronoun "its."
In short, "before" is not a word that can be an antecedent because it is not a noun or pronoun.