Reply To: Who should be called Rabbi?

The mishna says in Pirkei Avos that if a person learns even one letter from someone, he is suppose ro call him rabbi which literally means my teacher. David learned two things alone from Doag and he called him rabbi.
The question is how do we know one letter? Explains the Besht that sometimes one letter is more productive than two things alone. We learn from one letter that addition really diminishes.