¿Conoce a un buen dentista?
Hi i'm fairly new to Spanish, and trying to get my head around the grammar.
What is the purpose of the "a" in this instance?
4 Answers
It is called the personal "a" and is used when speaking about people.
Veo a mi hermana. I see my sister.
It's not used with things.
Veo el carro. I see the car.
Welcome to the forum. 
It is also not used when the dentist is unknown to you.
¿Conoces un buen dentista? is also correct.
If the direct object is an indefinite person, the personal "a" is not used. The result is that the person becomes "depersonalized."
You're sentence would be more like "You know a good dentist, don't you?". I know that you and Dr. Smith, the dentist, are friends, but asking is more polite.
The concept is carried over to animals if you read the article. If you know the animal (have feelings for it, it is a pet) you use the personal a. If it is a wild or domesticated animal that you don't have feelings for (one cow among many in a herd) the personal a is not used.
Thanks everyone, all those explanations make perfect sense!
Hi, Scotty, welcome to the forum. Just to add a little to Delores-Lin's excellent explanation, the "personal a" is used before direct objects that refer to people or pets. In all of her examples, she has given you direct objects that either refer to people or to things, to show you the contrast.
