Vocative case

The vocative case is the form used to address someone directly, to call or name the person you are speaking to. When you translate it, it usually comes out as "O..." or simply as the name set off by commas: "Marcus, come here!"

English does not change a name when we call out to it; "Marcus!" looks the same whether it is a subject or a shout. Latin behaves the same way for most nouns: the vocative is identical to the nominative. There is just one common exception worth learning now.

Noun type	Nominative	Vocative
1st decl.	puella	puella (same)
2nd in -us	servus	serve
2nd in -ius	Marcus / fīlius	Marce / fīlī

So second-declension masculine nouns ending in -us change to -e, and names in -ius end in a single -ī.

• Salvē, amīce! - Hello, friend!
• Quid agis, Marce? - How are you, Marcus?
• Venī, fīlī! - Come, son!

The error to avoid is leaving servus or Marcus unchanged when addressing someone. Roman Latin says serve and Marce. Everywhere else, if a noun is not one of these -us/-ius types, the vocative simply matches the nominative.