Question

When is the “a” personal used in Spanish?

The “a” personal is used when the direct object is an indefinite person.

The “a” personal is used when the direct object of a sentence is a person.

The “a” personal is used when there is a direct object in the sentence.

Every sentence has the “a” personal.

Answer 1

The best answer is the second: "The ‘a’ personal is used when the direct object of a sentence is a person."

Clarification and key points:
- More precisely: use the personal a when the direct object is a specific person or people (or a personified animal).
- Examples: Veo a María. / Ayudo a mi madre. / Escuché a los niños.
- Do not use it with inanimate direct objects: Veo la casa. No *a*.
- With indefinite or nonspecific people the a is often omitted: Necesito un doctor. (but see note on search/context below)
- With alguien, nadie, quien you still use it: No conozco a nadie. / ¿Ves a quien llegó?
- Pets treated as persons commonly take the a: Amo a mi perro.
- The preposition a is also used to mark indirect objects (Le doy el libro a Juan), which is a different function from the personal a.

So the other three statements are incorrect or overly broad.