It depends who you ask, and what region of the world you're talking about. And whether youre talking about speaking to the person, or addressing a missive...
In speech:
A Grand Duke sits just below the royalty, and would probably be addressed as "Your Royal Highness.
Then a Duke is often addressed as "Your Grace", occasionally "Your Highness".
Below the Duke, a count or countess would be addressed as "Your Excellency"
Below that, you have barons and such (whcih vary a bit from place to place) - the basic form of address would be "Your Excellency".
Down below the baron, you get various forms of knights, who are "Sir" or "My Lord".
In speech:
A Grand Duke sits just below the royalty, and would probably be addressed as "Your Royal Highness.
Then a Duke is often addressed as "Your Grace", occasionally "Your Highness".
Below the Duke, a count or countess would be addressed as "Your Excellency"
Below that, you have barons and such (whcih vary a bit from place to place) - the basic form of address would be "Your Excellency".
Down below the baron, you get various forms of knights, who are "Sir" or "My Lord".
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