Latin Adjectives 1st and 2nd Declension

It is confusing to those learning Latin that nouns and adjectives do not have to be in the same declension.

In Latin, adjectives must agree with the nouns they modify in case and number, as well as gender. This means that like nouns, Latin adjectives must be declined.* Latin 1st and 2nd declension adjectives are declined like nouns in the 1st and 2nd declensions, but be careful. It so happens that like nouns, there are also 3rd declension adjectives, but this is coincidence and there are no 4th or 5th declension adjectives. So, since there are more declensions for nouns than adjectives, the number of the declension of the noun cannot possibly have to match the number of the declension of the adjective. It's even misleading to think of adjectives as belonging to the 1st OR the 2nd declension. They belong to both but look different depending on gender. For this reason, it's better to refer to such adjectives as 1st AND 2nd declension adjectives.

The Latin from which we get our word "republic" comes from a 5th declension feminine noun (res) and a feminine adjective (publica). If the 5th declension noun were masculine (e.g., meridies 'midday'), the adjective would take the masculine form publicus.

As stated above, Adjectives need to match only the gender, number, and case of the noun they modify.

A first and second declension adjective can modify any noun.

The first and second declension adjective used here as a model is bonus, -a, -um, the Latin word for "good" showing the full masculine form first, followed by the ending of the feminine next, and finally the ending for the neuter.

1. The word "girl" is puella in Latin, a first declension noun, and like most first declension nouns, it's feminine. The adjectival form corresponding with puella -- a noun in the nominative singular -- is bona.

   Declension of Bona Puella (Good Girl) in Latin:

   Singular
   • nominative bona puella
   • genitive bonae puellae
   • dative bonae puellae
   • accusative bonam puellam
   • ablative bona puella
   Plural
   • nominative bonae puellae
   • genitive bonarum puellarum
   • dative bonis puellis
   • accusative bonas puellas
   • ablative bonis puellis
2. The word for "boy" in Latin is puer. This is the nominative singular of a second declension masculine noun. The form of the model adjective we're using, that corresponds with puer -- that is, the form of the adjective that agrees in number, case, and gender -- is bonus.

   Declension of Bonus Puer (Good Boy) in Latin:

   Singular
   • nominative bonus puer
   • genitive boni pueri
   • dative bono puero
   • accusative bonum puerum
   • ablative bono puero
   Plural
   • nominative boni pueri
   • genitive bonorum puerorum
   • dative bonis pueris
   • accusative bonos pueros
   • ablative bonis pueris
3. The English word "word" is verbum in Latin. This is a second declension neuter noun. The form of the model adjective "good" that corresponds with verbum is bonum. Note that since this is a neuter, we can not say whether bonum verbum is nominative or accusative, although it is clearly singular.

   Declension of Bonum Verbum (Good Word) in Latin:

   Singular
   • nominative bonum verbum
   • genitive boni verbi
   • dative bono verbo
   • accusative bonum verbum
   • ablative bono verbo
   Plural
   • nominative bona verba
   • genitive bonorum verborum
   • dative bonis verbis
   • accusative bona verba
   • ablative bonis verbis

The paradigm form you will usually see for a 1st and 2nd declension adjective is:

bonus -a -um
boni -ae -i
bono -ae -o
bonum -am -um
bono -a -o

boni -ae -a
bonorum -arum -orum
bonis -is -is
bonos -as -a
bonis -is -is

*You may run into indeclinable adjectives, which, obviously, are not declined.