How to Address Your Professors
Refer to your professor by the title "Professor" or "Dr.". You should never address them by "Mr." or "Ms.",
because some people consider it insulting due to the fact it does not acknowledge
their credentials. Likewise, you should avoid the term "sir", since in the U.S. it is
considered impersonal and also ignores the fact the person you are addressing has
an advanced degree.
(The term "sir" is sometimes
used in other countries to address teachers or professors, but
it is not considered common or proper in most
U.S. universities or colleges.)
If your professor has a Ph.D, you should address them
as "Professor LastName" or "Dr. LastName". If they do not have a Ph.D., or if
you are not sure,
address them simply as "Professor LastName".
Results of a Survey asking U.S. academics how to address a Professor.