Maybe a single column (and formula) will do?
Code:
=IF(
IFERROR(1*(FIND("doctor",$A2)>0),0)+IFERROR(2*(FIND("professor",$A2)>0),0)=0;
"",
INDEX(
{"doctor";"professor";"doctor and professor"},
IFERROR(1*(FIND("doctor",$A2)>0),0)+IFERROR(2*(FIND("professor",$A2)>0),0)
)
)