The word "doctor"

My friend has a story of his son knowing that the boy’s father is somehow a “doctor” but “not the kind that helps people.” My friends take a bit of offense!  Of course, we “help” people!  What about all those lessons we taught?  Huh?  Huh?  What about that?

I understand that the title ‘doctor’ was invented as the third level in advanced learning, much like the three levels in a guild of “apprentice, journeyman and master”, as in master carpenter or master plumber.  The three levels of “graduate, master and doctor” are often used to indicate levels of learning in colleges and universities.  We still have the word “physician” to mean specifically a person having knowledge and skills (hopefully) to assist people with problems with their bodies.  If you fall and break some bones, you may want help from a physician, not a doctor of Spanish literature.