Vocative

When we call someone by name, we use a form of the name called the "vocative". Here are the basic rules for making a vocative:

• If a name ends in "-ius", then the vocative ends in "-i". "Tullius" becomes "Tulli".
• If a name ends in "-us", then the vocative ends in "-e". "Marcus" becomes "Marce".
• All other names do not change at all. "Felix" stays "Felix", "Marca" stays "Marca" and so on.

There is a complete discussion of *which* name you should use at Choosing_a_Roman_name#Which_Names.3F .

It is a good idea in general to use the cognomen (the last part of the name).

• To say hello to Marcus Lucretius Agricola you would write "Salve Agricola!".
• To say hello to Aulus Apollonius Cordus you would write "Salve Corde!".
• To say hello to Gaius Equitius Cato you would write "Salve Cato!".

Only if you are very close friends indeed with these people you could write:

• "Salve Marce!"
• "Salve Aule!"
• "Salve Gai!"