In the sentence "They must have left late," the word "they" serves as what part of speech?

In the sentence "They must have left late," the word "they" functions as a pronoun. Pronouns are words used to replace nouns in order to avoid repetition and make sentences clearer. Specifically, "they" is a personal pronoun that refers to a group of people or individuals previously mentioned or assumed in context.

In this case, "they" stands in for a noun, which could be the names of people or things, thereby simplifying the sentence and making it fluid. The context of the sentence implies a subject performing the action, and the use of "they" effectively fulfills that role. By identifying "they" as a pronoun, we understand that it operates as a subject in the sentence, clarifying who is taking the action of leaving.