4.2 Third declension adjectives

Types of Third Declension Adjectives

Third declension adjectives expand Latin's descriptive toolkit beyond the familiar first/second declension $-us, -a, -um$ pattern. They come in three types based on how many distinct forms they have in the nominative singular. All three types share the same set of case endings once you get past the nominative.

Two-termination adjectives

These have two forms in the nominative singular: one shared by masculine and feminine ($-is$), and a separate neuter form ($-e$).

• fortis, forte (brave): $fortis$ covers both masculine and feminine, $forte$ is neuter
• The masculine and feminine share the same form in every case, not just the nominative
• Other common examples: omnis (all, every), brevis (short), dulcis (sweet), gravis (heavy)

This is the most common type of third declension adjective, so get comfortable with it.

Three-termination adjectives

These have a separate nominative singular form for each gender: $-er$ (m.), $-ris$ (f.), $-re$ (n.).

• acer, acris, acre (sharp, keen)
• celer, celeris, celere (swift)
• saluber, salubris, salubre (healthy)

Outside the nominative singular, the masculine and feminine forms are identical, just like two-termination adjectives. The three distinct forms only matter in the nominative (and vocative) singular.

Note that some of these drop the $-e-$ before $-r$ in the masculine nominative (like acer from stem acri-), while others keep it (like celer from stem celeri-). You need to memorize which do which.

One-termination adjectives

These use a single nominative singular form for all three genders.

• felix (happy, fortunate): $felix$ for masculine, feminine, and neuter nominative singular
• audax (bold), prudens (wise), sapiens (wise), vetus (old), pauper (poor)

The neuter only looks different from the masculine/feminine in the accusative singular and the nominative/accusative plural. In the nominative singular, all genders are the same.

Stem Formation

To decline any third declension adjective, you first need to find its stem. The stem is what you attach case endings to.

Finding the stem

1. Look up (or recall) the genitive singular form, which always ends in $-is$
2. Remove the $-is$
3. What remains is the stem

I-stems vs. consonant stems

This distinction matters because it changes several endings:

I-stem adjectives retain an $-i-$ in certain forms. Most two-termination and three-termination adjectives are i-stems, along with many one-termination adjectives (like felix, stem felici-). Their key features:

• Ablative singular: $-i$ (not $-e$)
• Genitive plural: $-ium$ (not $-um$)
• Neuter nominative/accusative plural: $-ia$ (not $-a$)

Consonant-stem adjectives are fewer in number. The main ones to know are vetus (veter-), pauper (pauper-), and dives (divit-). These decline more like consonant-stem nouns:

• Ablative singular: $-e$
• Genitive plural: $-um$
• Neuter nominative/accusative plural: $-a$

Case Endings

Masculine and feminine endings

Neuter endings

Irregular forms

A few adjectives break the standard pattern:

• plus (more) is unusual: the singular is only neuter ($plus$, genitive $pluris$), while the plural works normally ($plures, plura$)
• vetus (old) keeps $-us$ in the nominative singular for all genders and uses consonant-stem endings throughout
• Comparative adjectives like fortior, fortius use $-ior$ (m./f.) and $-ius$ (n.) in the nominative singular, then decline as consonant stems

Agreement with Nouns

Every adjective in Latin must agree with its noun in three ways: gender, number, and case. This doesn't mean the adjective and noun will have the same endings. A third declension adjective modifying a first declension noun will have different endings but still match in gender, number, and case.

Gender agreement

• Three-termination adjectives show gender clearly in the nominative: $acer$ (m.), $acris$ (f.), $acre$ (n.)
• Two-termination adjectives distinguish only neuter: $fortis$ (m./f.) vs. $forte$ (n.)
• One-termination adjectives look the same for all genders in the nominative: $felix$ for m., f., and n.

Number agreement

Adjectives must be singular when their noun is singular, plural when plural. Watch the neuter plural especially: i-stem adjectives use $-ia$ (e.g., $omnia$), while consonant stems use $-a$ (e.g., $vetera$).

Case agreement

The adjective takes whatever case the noun has, regardless of where the adjective sits in the sentence. Latin word order is flexible, so the adjective might be far from its noun. You identify the pairing by matching gender, number, and case, not by proximity.

The ablative singular is a useful diagnostic: if you see $-i$, you're likely dealing with an i-stem adjective; if you see $-e$, it's probably a consonant stem.

Comparison to Other Declensions

First and second declension vs. third

A third declension adjective can modify a noun of any declension. For example, $vir fortis$ pairs a second declension noun with a third declension adjective. The endings won't match, but gender, number, and case do.

Similarities with third declension nouns

Third declension adjectives share most endings with third declension nouns: $-is$ for genitive singular, $-es$ for nominative plural (m./f.), $-ibus$ for dative/ablative plural. The i-stem vs. consonant-stem distinction works the same way for both nouns and adjectives.

Common Third Declension Adjectives

Frequently used examples

Irregular adjectives

• plus: singular is neuter only ($plus, pluris$); plural declines regularly ($plures, plura, plurium$)
• vetus: uses $-us$ in nominative singular for all genders; consonant-stem endings throughout (ablative $vetere$, genitive plural $veterum$)
• dives (rich): has a mixed pattern, sometimes following third declension forms ($dives, divitis$) and sometimes using contracted forms ($dis, ditis$)

Adjective Placement

Attributive position

In prose, adjectives typically follow the noun they modify: $vir fortis$ (a brave man). Placing the adjective before the noun adds emphasis: $fortis vir$ stresses the bravery. In poetry, adjectives and their nouns are often separated by other words.

Predicative position

A predicative adjective is separated from its noun and connected through a linking verb (usually a form of $esse$). Compare:

Uses in Sentences

As modifiers

Third declension adjectives modify nouns in any grammatical role:

• Subject: $vir fortis pugnat$ (the brave man fights)
• Direct object: $virum fortem video$ (I see the brave man)
• With prepositions: $cum viro forti$ (with the brave man)

The adjective always agrees in gender, number, and case with the noun it modifies.

As substantives

When used without a noun, an adjective functions as a noun itself. The gender tells you what's implied:

• $sapientes$ (masculine plural) = "wise men" or "wise people"
• $omnia$ (neuter plural) = "all things"
• $boni$ (masculine plural) = "good people"

In English you'll often need to supply a word like "people," "men," "women," or "things" depending on the gender and context.

Declension Patterns

Singular declension (i-stem example: fortis, forte)

Plural declension (i-stem example: fortis, forte)

For consonant-stem adjectives (like vetus), the key differences are: ablative singular $-e$ ($vetere$), genitive plural $-um$ ($veterum$), and neuter nominative/accusative plural $-a$ ($vetera$).

Pronunciation and Stress

Stress rules

Latin stress follows predictable rules that apply to adjective forms just as they do everywhere else:

1. Two-syllable words: stress the first syllable ($FOR-tis$)
2. Three or more syllables with a long penult: stress the penultimate ($fe-LI-cis$)
3. Three or more syllables with a short penult: stress the antepenultimate ($CE-le-res$)

Common pronunciation challenges

• Short vs. long vowels in endings can distinguish forms: $fortis$ (genitive singular, short $-i-$) vs. $fortīs$ (dative/ablative plural, long $-ī-$)
• Consonant clusters in stems like $prudens$ or $pulcher$ need careful articulation
• When enclitics like $-que$ are added, stress shifts: $fortísque$

Translation Strategies

Identifying adjectives in Latin texts

1. Look for characteristic third declension endings ($-is, -em, -i, -e, -es, -ium, -ibus$)
2. Check whether the word agrees with a nearby noun in gender, number, and case
3. Use context to distinguish adjectives from nouns that look similar ($fortis$ the adjective vs. $hostis$ the noun both end in $-is$)
4. Watch for predicative adjectives that may be separated from their noun by a verb

Rendering in English

• Attributive adjectives translate straightforwardly: $vir fortis$ = "a brave man"
• Predicative adjectives need a linking verb in English: $vir fortis est$ = "the man is brave"
• Substantive adjectives require you to supply an English noun: $omnia$ = "all things," not just "all"
• Some Latin adjectives carry nuances that need a phrase in English: $felix$ can mean "happy," "fortunate," or "blessed" depending on context