Declension: General Rules
Latin nouns don't sit still. Every noun shifts its ending to show what job it's doing in the sentence — subject, possessor, indirect object, direct object, instrument — and Latin sorts every noun into one of five declensions based on its stem vowel.
Once you know the declension, the case-endings are predictable.
The trap is that the same ending can mean different things in different declensions: -ae is genitive singular AND nominative plural in the first declension, but dative singular only in the third.
The shape of the word doesn't tell you what it's doing — the declension does. This page surveys the system: the cases and what each one signals, the seven big rules that hold across all five declensions, and the Roman three-name convention you'll meet in every author.
Stem vowel + genitive singular ending sort every Latin noun into one of five families.
The genitive singular is the diagnostic. The dictionary always gives it — once you have it, you have the declension and the stem.
| Case | Case | I (F.) | II (M.) | II (N.) | III (M./F.) | III (N.) | IV (M.) | IV (N.) | V (F.) |
|---|---|---|---|---|---|---|---|---|---|
| Nom. | — | -a | -us | -um | -s | (stem) | -us | -ū | -ēs |
| Gen. | — | -ae | -ī | -ī | -is | -is | -ūs | -ūs | -ēī |
| Dat. | — | -ae | -ō | -ō | -ī | -ī | -uī | -ū | -ēī |
| Acc. | — | -am | -um | -um | -em | (= nom.) | -um | -ū | -em |
| Abl. | — | -ā | -ō | -ō | -e | -e | -ū | -ū | -ē |
| Voc. | — | -a | -e | -um | (= nom.) | (= nom.) | -us | -ū | -ēs |
| Case | Case | I | II (M.) | II (N.) | III (M./F.) | III (N.) | IV (M.) | IV (N.) | V |
|---|---|---|---|---|---|---|---|---|---|
| Nom./Voc. | — | -ae | -ī | -a | -ēs | -a, -ia | -ūs | -ua | -ēs |
| Gen. | — | -ārum | -ōrum | -ōrum | -um, -ium | -um, -ium | -uum | -uum | -ērum |
| Dat./Abl. | — | -īs | -īs | -īs | -ibus | -ibus | -ibus | -ibus | -ēbus |
| Acc. | — | -ās | -ōs | -a | -ēs | -a, -ia | -ūs | -ua | -ēs |
See It In Action
— B. G. i. 1. 1
Three different declensions in one famous opening: Gallia (1st), omnis and partēs (3rd), in the same nine words. The endings tell you the case; you have to know the declension to know what each ending means.
— Cic. Cat. i. 1
Catilīna is the vocative — direct address. Most declensions have voc. = nom., but here a 1st-decl. masculine name shows the voc. plainly because it sits in the middle of the sentence, set off by commas — that's the give-away.
— B. G. iii. 11. 1
T. is the praenōmen Titus, abbreviated as Romans always abbreviate the personal name. Labiēnum is the nōmen in the accusative — Caesar refers to his own officers by praenōmen + nōmen, the standard formal style.
In the 1st declension, -ae does THREE jobs. The shape alone never tells you which.
"of the…" or "to/for the…" (singular)
fīlia agricolae
the daughter of the farmer
subject (plural)
agricolae labōrant
the farmers are working
Tip: Ask whether the -ae word is doing the verb (nom. pl.) or attached to another noun (gen. sg.) or receiving something (dat. sg.). The verb's number and the surrounding nouns decide.
You meet the noun cōnsulis in a Caesar sentence. Which declension is it, and what is its stem?
Study Tips
- •Memorize the five declension characteristics (-ā, -ŏ, -ĭ/cons., -ŭ, -ē) and the gen. sg. ending for each — that pair tells you everything else.
- •When you spot a new noun, the genitive singular is the key: it tells you the declension AND gives you the stem (drop the gen. ending).
- •Know the seven general rules in §38 cold. Neuters always have nom. = acc. and plural -a. Dat. = abl. in the plural. Gen. pl. always ends in -um. These rules cut your memorization in half.
- •When you see a Roman name in three parts (M. Tullius Cicerō), don't translate the praenōmen — abbreviations like M., L., Q. are personal names you keep in English.