Nominative and accusative case

Case

Nouns can take on a number of different roles in a sentence:

role of “Quintus”
Quintus returns. subject
Horatia greets Quintus. object of verb
Horatia walks towards Quintus. object of preposition

In Latin, nouns indicate their role in a sentence by changing their form.

role of “Quintus”
Quintus redit. subject
Horatia Quintum salutat. object of verb
Horatia ad Quintum ambulat. object of preposition

This system of roles and forms is called case.

Role → case → form

Here is how case works. Every noun in a sentence has a role. A noun’s role in its sentence gives it a case.

if a noun’s role in a sentence is: its case is:
subject nominative case
object of verb accusative case
object of preposition accusative case (or ablative case)

Nouns indicate their case by changing their form.

nominative case formaccusative case form
puella puellam words ending in ·a
via viam
colonus colonum most words ending in ·us
Quintus Quintum
puer puerum some words ending in ·er
ager agrum other words ending in ·er

Most Latin nouns have an accusative case form which ends in ·m.