All nouns of the third declension end in -is in the genitive singular. Remember that the genitive singular ending tells us which declension a noun belongs to, while the nominative ending may vary. To review:
| Declension | Genitive Ending | Example |
|---|---|---|
| First | -ae | puella, puellae, girl |
| Second | -ī | amicus, amicī, friend ager, agrī, field |
| Third | -is | rēx, rēgis, king |
We saw some variety in the nominative endings in the second declension, but in the third declension the nominative singular endings are all over the place, so it's even more critical to memorize the nominative and genitive singular together. Also, we learned that most first declension nouns are feminine while most second declension nouns are masculine and neuter. Third declension nouns belong to all three genders, but we'll deal with the neuter ones in the next lesson.
Masculine and feminine nouns of the third declension take the same endings. As usual, we drop the -is ending from the genitive singular to get the stems, and add the third declension endings. To decline frāter (brother) and soror (sister):
| Singular | Endings | ||
|---|---|---|---|
| Nominative | frāter | soror | (varies) |
| Genitive | frātris | sorōris | -is |
| Dative | frātrī | sorōrī | -ī |
| Accusative | frātrem | sorōrem | -em |
| Ablative | frātre | sorōre | -e |
| Plural | Endings | ||
|---|---|---|---|
| Nominative | frātrēs | sorōrēs | -ēs |
| Genitive | frātrum | sorōrum | -um |
| Dative | frātribus | sorōribus | -ibus |
| Accusative | frātrēs | sorōrēs | -ēs |
| Ablative | frātribus | sorōribus | -ibus |
A few things to notice that might help us learn the endings: The accusative singular again ends in 'm' while the plural ends in 's', similar to the -am and -as of the first declension and -um and -os of the second declension masculine. The dative and ablative plural have the same ending again. The genitive plural -um ending is similar to the -arum and -orum of the first two declensions.
In the Roman Republic (about 500 B.C. to 30 B.C.) the executive power was held by two consuls, who were elected annually. The consuls also served as generals in times of war.
The power to rule was called the imperium. First this was held by the king, then in Republican times by the consuls, and later by the emperors.
A general who achieved great success in war might be called imperator, which meant “wielder of the imperium,” and could take that as his title. Later the emperors took the title for themselves.
This lesson only covered one thing, because there are a lot of third declension words, so it's important to learn it well. Next lesson we'll deal with neuter nouns of the third declension, which won't really present much that's new.
| Singular | Plural | |
|---|---|---|
| Nom. | pater noster | patres nostri |
| Gen. | patris nostri | patrum nostrorum |
| Dat. | patri nostro | patribus nostris |
| Acc. | patrem nostrum | patres nostros |
| Abl. | patre nostro | patribus nostris |
| soror mea | sorores meae |
| sororis meae | sororum mearum |
| sorori meae | sororibus meis |
| sororem meam | sorores meas |
| sorore mea | sororibus meis |
| rex novus | reges novi |
| regis novi | regum novorum |
| regi novo | regibus novis |
| regem novum | reges novos |
| rege novo | regibus novis |
| consul malus | consules mali |
| consulis mali | consulum malorum |
| consuli malo | consulibus malis |
| consulem malum | consules malos |
| consule malo | consulibus malis |