It is the meaning of "personal" in these kinds of pronouns. It all depends on how you're looking at things.
What is "perspective"?
These words modify nouns or pronouns.
What are adjectives?
This helping verb is needed for all future tenses.
What is "will"?
There are this many sentence types.
What are four?
These words modify themselves.
What are adverbs?
This is helping verb required for continuous (progressive) tenses.
What is "be?"
This is the sentence type that is used most.
What is declarative?
These are the adverb questions.
What is "when, where, why, and how"?
These are the helping verbs required for perfect tenses.
What is "have"?
This is the sentence type for asking questions.
What is interrogative?
These are the adjective questions.
What are "which, how many, whose, and what kind"?
This is the ending for the main verb in continuous (progressive) tenses.
What is "ing"?
This is the sentence type for commands.
What is imperative?
Alone, these small words can be adverbs, but usually they're in a phrase.
What are prepositions?
This is one of only two verb tenses that do not require a helping verb.
What is simple past or simple present?
This is the sentence type for intense emotions.
What is exclamatory?