Adiectīva I (1·2 Dēclīnātiōnis)

An adjective (adiectīvum) is a word added to a noun to qualify or limit its meaning — to specify which one, what kind, or how much. Latin adjectives are inflected for gender, number, and case to agree with the noun they modify. This three-fold agreement (cōncordia) is the fundamental Latin rule, simpler in principle than complex in practice.

Latin adjectives fall into two great classes:

(1) Adjectives of the first and second declension — with three sets of endings: masculine declines like servus or puer; feminine like stella; neuter like bellum. Roughly half of all Latin adjectives belong here. They are the simplest and most regular.

(2) Adjectives of the third declension — inflected as i-stems. Subdivided by how many distinct nominative singular forms they show: three (ācer, ācris, ācre), two (fortis, forte), or one (vetus; audāx, audācis; prūdēns, prūdentis).

The lexicon enters an adjective by giving its three nominative singular forms (or, when one form serves multiple genders, with the genitive singular for verification). Examples:

• bonus, bona, bonum — three forms (1·2-decl. standard).
• miser, misera, miserum — three forms (1·2-decl. -er, e- preserved).
• pulcher, pulchra, pulchrum — three forms (1·2-decl. -er, e- dropped).
• ācer, ācris, ācre — three forms (3-decl. type).
• fortis, -e — two forms (3-decl. type).
• vetus, veteris — one form + genitive (3-decl. cons.-stem type).
• audāx, -ācis — one form (3-decl. i-stem).
• prūdēns, -entis — one form (-ns participle-type).

The most common pattern is bonus, -a, -um, "good". The masculine declines like servus, the feminine like stella, the neuter like bellum. There is no innovation: the adjective inherits the full noun-paradigms of the first and second declensions.

Adjectives ending in -er follow the pattern of puer or ager: some keep e throughout the inflection (miser, misera, miserum — the "-er stems"); others drop e in all forms except the nominative singular masculine (pulcher, pulchra, pulchrum — the "-r stems").

The decision between the two patterns reflects the historical phonology: original stems with -r- following a consonant tend to drop e; stems with -er- as part of the root tend to preserve it. This is unpredictable from the nom. sg. masculine alone — one must learn the feminine.

Words declining like miser (e- preserved): tener (tender), asper (rough), līber (free), prosper (favorable), lacer (torn), satur (satisfied).

Words declining like pulcher (e- dropped): aeger (sick), niger (black), integer (whole, intact), sacer (sacred), noster (our), vester (your, pl.), piger (lazy), aegrōtus (sick — but cf.; this declines like bonus actually).

Possessive adjectives noster and vester follow this pattern strictly.

Nine adjectives of the first and second declension take the genitive singular in -īus (with long i) and the dative singular in -ī, regardless of gender. They are mnemonic-friendly:

UNUS NAUTA: ūnus, nūllus, ūllus, sōlus, neuter, alius, alter, uter, tōtus.

Translation: ūnus (one), sōlus (alone), tōtus (whole), ūllus (any), nūllus (none), alius (other), alter (one of two), uter (which of two), neuter (neither).

These are identical to bonus in all cases except:
• Genitive singular (all genders): -īus instead of expected -ī, -ae, -ī.
• Dative singular (all genders): -ī instead of expected -ō, -ae, -ō.

The other cases are perfectly regular (and identical to bonus). alius (= "another, different one") borrows the genitive alterīus (from alter) for euphony — the regular form would be aliīus, which is awkward. Hence alterīus serves both alter and alius.

The pattern is shared with the demonstrative pronouns hic, ille, iste, is, īdem and the relative/interrogative quī, quae, quod / quis, quid — all share -īus gen. and -ī dat. This is a major Indo-European archaism preserved across Latin's pronominal system.

Latin adjectives are freely used as nouns — a key economy of the language. The masculine usually denotes a male person; the feminine, a female; the neuter, a thing or quality.

Masculine: bonus "a good man"; fortis "a brave man"; amīcus "a friend"; inimīcus "an enemy" (note: as nouns, fully lexicalized — listed in dictionaries).

Feminine: bona "a good woman"; amīca "a (female) friend"; inimīca "a (female) enemy".

Neuter singular: bonum "a good thing, the good"; vērum "the truth"; magnum "the great (thing)"; iūstum "the just (thing)"; summum bonum "the highest good" (philosophical idiom).

Neuter plural: a major Latin idiom — abstract or collective ideas: bona "good things, blessings, possessions, goods"; mala "evils"; multa "many things"; omnia "all things"; parva "little things". The neuter plural can be used to refer to philosophical or moral abstracts almost as nouns: bona et mala "the good and the bad".

Many such substantives are fully lexicalized: amīcus (friend), inimīcus (enemy), aequālis (equal, peer), vērum (truth), bona (goods, property), arma (arms — n. pl. only), iūsta (rites).

An adjective agrees with its noun in gender, number, and case. This is the fundamental principle of Latin syntax for adjectives. The agreement is morphological — visible in the inflection of both noun and adjective.

Examples:
• vir bonus "a good man" (m.sg.nom.) — both nominative singular masculine.
• fēmina bona "a good woman" (f.sg.nom.).
• cōnsilium bonum "a good plan" (n.sg.nom.).
• virōs bonōs "good men" (m.pl.acc.).
• cum amīcīs cārīs "with dear friends" (m.pl.abl.).

An adjective modifying two or more nouns: rules:

(a) Same gender: adjective is plural in that gender. vir et puer fortēs "a brave man and boy" (m.pl.).

(b) Different genders, persons: masculine prevails. vir et fēmina bonī "the good man and woman" (m.pl.).

(c) Things, neuter prevails: arma et iacula nova "new arms and javelins" (n.pl.).

(d) Person and thing: the noun closer to the adjective often wins, or each noun gets its own adjective.

Predicate adjectives after a linking verb (sum, fīō, videor, putor) follow the same rules through the linking verb: vir bonus est "the man is good" (predicate adjective in nom. agreeing with subj.); fēminae bonae sunt "the women are good".

The morphological flexibility of Latin allows great word-order freedom: because the agreement signals the syntactic relation, the adjective can stand far from its noun for stylistic effect: magnam ille gerit cum hostibus pugnam "He wages a great battle with the foes" (Vergil-style hyperbaton).