I am just beginning learning some Italian, and I noticed that there are at least 2 ways for feminine forms to arise from titles whose masculine form end in
ore, namely this ending can change to
signore --> signora
dottore --> dottoressa
professore --> professoressa
Why the difference in these ways of forming the feminine forms? More generally, what are the rules for forming feminine forms of nouns (or titles if it's different), say whose masculine form ends in
ore if it helps to be more specific)?