Forms of address are the easiest way to flatter (or insult!) the person with whom you are speaking. Addressing a person with a greeting above her/his station will flatter; using a greeting below her/his station will result in wounded pride, perhaps even a duel if the slighted individual feels strongly enough about the matter.

"You" is for your betters; i.e., anyone more noble or wealthy than you. And horses, as they are considered noble creatures. "Thou" is for friends, family, lovers, pets, and God. The Grand Duke, Duchessa, and any King/Queen are never addressed as "thou"!

A King or Queen is always "Your Majesty".

A Prince or Princess is always "Your Highness".

The Grand Duke is always "Your Grace" or "My Lord Duke". His friends may call him "Don Cosimo" if he consents. His Italian form of address is "Il Serenissimo" or "Serenissimo Altezzo".

The Duchessa is always "Your Excellency" (most formal), "Duchessa Rossetti" or "Donna Rossetti" or "Ma Donna" (more casual). Her friends may call her "Donna Lucia" if she consents. The Italian form is "Sua Eccelenza".

The Knights of Santo Stefano are addressed as "Don", i.e., Don Francesco, Don Gianni, etc. Esquires are addressed as "Messer", i.e. Messer Niccolo.

The Ladies of Santa Zita are addressed as "Monna", i.e. Monna Margherita, Monna Annabella.

Children of nobles, unless they bear their own titles, are addressed as "Messer" or "Monna", i.e. Messer Giannotto, Monna Caterina.

FORMS OF ADDRESS FOR ENGLISH PERSONS

Sample name: Francis Russell, Earl of Bedford
(first) (surname) (title) (title name)

QUEEN (or a King, if you can find one) - Your Majesty

DUKE/DUCHESS - Your Grace or
Sir/Lady (surname) or Lord/Lady (title name)

MARQUIS/MARCHIONESS - Your Excellency or
Lord/Lady (surname)

EARL/COUNTESS - Your Excellency or
Sir/Lady (First name) or Lord/Lady (title name)

VISCOUNT/VISCOUNTESS - Your Honor or
Sir/Lady (First Name) or Lord/Lady (title name)

BARON/BARONESS - Your Lordship/Ladyship or
Lord/Lady (first name) or Lord/Lady (title name)

KNIGHT/KNIGHT'S LADY - My Lord/My Lady or
Sir (first name) or Lady (husband's full name) or
Master (surname) or Lady (surname)

It seems confusing, but takes only a bit of practice; you will pick it up without trying just by listening. Italian titles are much easier, and aren't you glad!

When addressing persons associated with nobles but not noble in their own right (children who are not heirs to nobles), "master" or "mistress" and the last name of the addressee is proper, i.e., "Master Wilkins", "Mistress Vernon". For all other persons, including servants, "master" or "mistress" with a first name is proper, i.e. "Master William" or "Mistress Margaret".