Here's why:
* Pronoun Case: In this phrase, "they" and "I" are both in the nominative case. This is the case used for subjects (the ones performing the action) and predicate nominatives (words that rename the subject).
* Conjunction: The word "and" connects the two pronouns, indicating that they are working together in the sentence.
Example:
* They and I are going to the movies. (They and I are the subjects of the verb "are going").
Let me know if you have any other grammar questions!