a Mr. Smith

[czildren]

hi guys,

What's the difference between saying a Mr. Smith and Mr.Smith?

Can a receptionist at hospital come and ask a patient: a Mr. Smith?
Does it mean that she hasnt met him before?

What is a difference between saying: "Ask a teacher" and "Ask the teacher"?

Thanks in advance

[Daruma]

a (an)
used before someone's name when you do not know who they are:
There is a Mr Tom Wilkins on the phone.

[Anglika]

But if the receptionist in a hospital or clinic is unsure that there is a patient with that name, she / he can go into the waiting room and ask "Is there a Mr Smith here?"

As to the teacher, "a teacher" means any teacher; "the teacher" is a specific teacher, maybe the one taking a particular class.