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. It so happens that like nouns, there are also 3rd declension adjectives, but 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 1st and 2nd declension adjective can modify any noun.
The 1st and 2nd 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.
- The word "girl" is puella in Latin, a 1st declension noun, and like most 1st 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
- nominative bonae puellae
- genitive bonarum puellarum
- dative bonis puellis
- accusative bonas puellas
- ablative bonis puellis
- The word for "boy" in Latin is puer. This is the nominative singular of a 2nd 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
- nominative boni pueri
- genitive bonorum puerorum
- dative bonis pueris
- accusative bonos pueros
- ablative bonis pueris
- The English word "word" is verbum in Latin. This is a 2nd 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
- nominative bona verba
- genitive bonorum verborum
- dative bonis verbis
- accusative bona verba
- ablative bonis verbis
bonus -a -um*You may run into indeclinable adjectives, which, obviously, are not declined.
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
Parts of Speech
- Latin Case - Ablatives
- Latin Case - Nominative
- Latin Case - Vocative
- Latin Cases - The 7 Cases of Latin Nouns, Pronouns, and Adjectives
- Latin Declension Rules
- Latin Noun Suffixes - List of Noun Suffixes in Latin
- Latin Nouns of the 1st Declension - Endings
- Latin Nouns of the 2nd Declension - Endings
- Latin Nouns of the 3rd Declension - Endings
- Latin Nouns of the 4th Declension - Endings
- Latin Nouns of the 5th Declension - Endings
- Latin Adjectives 1st and 2nd Declension
- Latin Adjectives for Masculine 1st Declension Nouns
- Endings on Latin Adjectives for the Comparative
- Latin Personal Pronouns
- Latin Demonstrative Pronouns
- Latin Intensive Pronoun Ipse
- Latin Interjections - List of Common Interjections in Latin
- Latin Conjunctions
- Latin Conjunctions - List of Conjunctions in Latin
- Prepositions With the Ablative - Latin Prepositions
It is confusing to those learning Latin that nouns and adjectives do not have to be in the same declension. The adjectives have to go with the nouns and matching declension seems the obvious way to do this, but it doesn't work that way. The 1st declension isn't actually feminine and the 2nd isn't actually masculine. Besides, there are 5 noun declensions, but there aren't 5 linguistic genders.