Lesson 14: Third Declension Adjectives
Two-termination, three-termination, and one-termination 3rd-declension adjectives, with the -ī/-e ablative distinction and the -ium genitive plural rule.
Overview
You already know 1st/2nd declension adjectives (bonus/bona/bonum). A large and important group of Latin adjectives follows 3rd declension patterns. These adjectives are classified by how many distinct nominative singular forms they have: three-termination, two-termination, or one-termination. All share common 3rd-declension endings in the other cases, but with i-stem characteristics.
1. Two-Termination: fortis, forte (brave, strong)
One form for M and F nominative singular, another for N. This is the most common type.
| Case | M/F | N |
|---|---|---|
| Nom. sg. | fortis | forte |
| Gen. sg. | fortis | fortis |
| Dat. sg. | fortī | fortī |
| Acc. sg. | fortem | forte |
| Abl. sg. | fortī | fortī |
| Nom./Acc. pl. | fortēs | fortia |
| Gen. pl. | fortium | fortium |
| Dat./Abl. pl. | fortibus | fortibus |
| Acc. pl. | fortēs | fortia |
2. Three-Termination: celer, celeris, celere (swift)
Separate nominative for all three genders. The masculine ends in -er (no -is), while feminine and neuter follow the two-termination pattern.
| Case | M | F | N |
|---|---|---|---|
| Nom. sg. | celer | celeris | celere |
| Gen. sg. | celeris | celeris | celeris |
| Dat. sg. | celerī | celerī | celerī |
| Acc. sg. | celerem | celerem | celere |
| Abl. sg. | celerī | celerī | celerī |
| Nom./Acc. pl. | celerēs | celerēs | celeria |
| Gen. pl. | celerium | celerium | celerium |
| Dat./Abl. pl. | celeribus | celeribus | celeribus |
Other three-termination adjectives: ācer, ācris, ācre (keen, sharp); puter, putris, putre (rotten).
3. One-Termination: fēlix, fēlicis (fortunate, happy)
All three genders share the same nominative singular. The genitive singular reveals the stem (fēlic-).
| Case | M/F | N |
|---|---|---|
| Nom. sg. | fēlix | fēlix |
| Gen. sg. | fēlicis | fēlicis |
| Dat. sg. | fēlicī | fēlicī |
| Acc. sg. | fēlicem | fēlix |
| Abl. sg. | fēlicī | fēlicī |
| Nom./Acc. pl. | fēlicēs | fēlicia |
| Gen. pl. | fēlicium | fēlicium |
| Dat./Abl. pl. | fēlicibus | fēlicibus |
Note: In one-termination adjectives, the neuter accusative singular = the nominative (fēlix), following the neuter rule.
4. The Ablative Singular: -ī vs. -e
This distinction matters for distinguishing 3rd-declension adjectives from 3rd-declension nouns in the ablative:
| Context | Ending | Example |
|---|---|---|
| Adjective (attributive/in agreement with a noun) | -ī | mīlite fortī (with the brave soldier) |
| Substantive (adjective used as a noun) | -e | ā fortī (by a brave man) |
| Predicative (after a linking verb) | -e | rēx fēlice would be unusual; predicative usually follows noun |
In practice: when a 3rd-declension adjective agrees with a noun, use -ī. When used alone as a noun, -e is sometimes seen. Grammars vary; the most important rule to remember is that 3rd-declension adjectives use -ī in the ablative singular, unlike most 3rd-declension nouns (which use -e).
5. Genitive Plural: Always -ium
Unlike most 3rd-declension nouns (which may use -um or -ium), 3rd-declension adjectives always take -ium in the genitive plural:
- fortium (of brave ones)
- fēlicium (of fortunate ones)
- omnium (of all)
6. Key Vocabulary — 3rd Declension Adjectives
| Adjective | Gen. sg. | English |
|---|---|---|
| fortis, forte | fortis | brave, strong |
| gravis, grave | gravis | heavy, serious, severe |
| brevis, breve | brevis | short, brief |
| levis, leve | levis | light (in weight) |
| dulcis, dulce | dulcis | sweet |
| tristis, triste | tristis | sad |
| omnis, omne | omnis | all, every |
| facilis, facile | facilis | easy |
| difficilis, difficile | difficilis | difficult |
| similis, simile | similis | similar |
| dissimilis, dissimile | dissimilis | dissimilar |
| fēlix, fēlicis | fēlicis | fortunate, happy |
| ingēns, ingentis | ingentis | huge, enormous |
| prūdēns, prūdentis | prūdentis | prudent, wise |
| audāx, audācis | audācis | bold, daring |
| vēlōx, vēlōcis | vēlōcis | swift |
| celer, celeris | celeris | swift, quick |
| ācer, ācris | ācris | keen, sharp, fierce |
Example Sentences
- Mīles fortis hostēs vīcit. — The brave soldier defeated the enemies.
- Iter breve erat. — The journey was short.
- Omnes discipulī Latīnam linguam amant. — All students love the Latin language.
- Vir prūdēns multa tacet. — A prudent man keeps silent about many things.
- Labor gravis est. — The work is serious/hard.
- Puer fēlix per agrōs currit. — The happy boy runs through the fields.
- Exercitus ingēns ad urbem vēnit. — A huge army came to the city.
- Dux audāx periculum non timet. — The bold leader does not fear danger.
- Facile est dicere; difficile est facere. — It is easy to speak; it is difficult to act.
- Vox fēminae dulcis erat. — The voice of the woman was sweet.
Practice
A. Identify the type (one/two/three-termination) and decline in the ablative singular:
- omnis, omne
- ingēns, ingentis
- celer, celeris, celere
B. Make the adjective agree with the noun (give correct form):
- puer + fortis (nominative singular)
- puellārum + fēlix (genitive plural)
- mīlitibus + audāx (dative/ablative plural)
- iter + breve (accusative singular)
C. Translate:
- Omnium virōrum fortissimus est Caesar. (Note fortissimus = bravest; parse omnium.)
- Vir prūdēns brevia verba dīcit.
- The kind of all difficult things is to begin. (Hint: use omnium rērum difficilium + est incipere.)