Declension

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Latin is an inflected language, and as such its nouns, pronouns, and adjectives must be declined in order to serve a grammatical function. A set of declined forms of the same word pattern is called a declension. There are five declensions, which are numbered and grouped by ending and grammatical gender.

This is a summary of the declension of Latin nouns.

Which declension a noun belongs to

Latin is a heavily inflected language, which means that Latin indicates grammatical information by changing the ending of the words. Nouns are grouped into five declensions (noun inflection groups). If we change a noun’s ending to express its grammatical role, we say we “decline” it. To determine which declension group a noun belongs to, you have to look into a Latin dictionary.

In the case of nouns, for example, “friend”, you will find:

amicus, -i, m.

This is 3 pieces of information:

(1) amicus;

(2) -i;

(3) m.

(1) amicus; This means that the word “friend” in nominative (subject) case is “amicus”.

(2) -i; The abbreviated form “-i” means that the word “friend” in genitive (possessive) case is “amici” (something of friend, or friend’s something), thus the original ending “-us” changes to “-i”. This is the most important point. This ending “–i” determines that “amicus” belongs to the “second declension”, whose identifier is the genitive “–i”. As we have mentioned, there are 5 declensions, and each one of these has a unique, declension-specific genitive ending. It’s important because the genitive ending determines the other inflections as well. The five types of genitive ending and the five declensions determined by the different genitive endings are:

-ae = 1st declension, e.g.: Roma, -ae, f (Rome)

-i = 2nd declension, e.g.: amicus, -i, m (friend)

-is = 3rd declension, e.g.: rex, regis, m (king)

-ús = 4th declension, e.g.: senatus, -ús, m (senate)

-ei = 5th declension, e.g. fides, -ei, f (loyalty)

(3) m.; The “m.” means that it is a masculine noun. In Latin, all nouns have three genders, they are masculine, (abbreviated as “m”), feminine (abbreviated as “f”), and neuter (abbreviated as “n”). English has a similar phenomenon when we use “he”, “she” or “it”. The new thing in this is that Latin uses these genders for things or abstract concepts, too, like in the exemples above, “loyalty” (fides, -ei, f) is feminine in Latin, the “senate” (senatus, -ús, m) is masculine, “Rome” (Roma, -ae, f) is, again, feminine.

How to decline a Latin noun

The declension (inflection ) of nouns is done by cutting off the declension specific genitive ending (-ae, -i, -is, -ús, -ei) and replacing them with the various case endings that you'll find below.

Neuter rule

Neuter nouns have no accusative form separate from their nominative. It means that all neuter nouns have accusatives identical to their nominatives, and, additionally, all neuter nouns have a plural nominative-accusative form that ends in -a, regardless to their declension group.

The "-rum/-ís" declension-group

The first and second declensions have common characteristics:

	First declension		Second declension
	A-Stem		O-Stem
	mf terra, -ae, f land		mf tribúnus, -í, m tribune		n auspicium, -í, n auspice
	Singular		Singular		Singular
Nominative	terra	——	tribúnus	——	auspicium	——
Accusative	terram	–am	tribúnum	–um	auspicium	——
Genitive	terrae	–ae	tribúní	–í	auspicií	–í
Dative	terrae	–ae	tribúnó	–ó	auspició	–ó
Ablative	terrá	–á	tribúnó	–ó	auspició	–ó
	Plural		Plural		Plural
Nominative	terrae	–ae	tribúní	–í	auspicia	–a
Accusative	terrás	–ás	tribúnós	–ós	auspicia	–a
Genitive	terrárum	–árum	tribúnórum	–órum	auspiciórum	–órum
Dative- Ablative	terrís	–ís	tribúnís	–ís	auspiciís	–ís

The "-um/-bus" declension-group

The third and fourth declensions have common characteristics:

	Third declension								Fourth declension
	Consonant Stem				I-Stem				U-Stem
	mf léx, légis, f law		n iús, iúris, n right		mf cívis, -is, mf citizen		n mare, -is, n sea		mf senátus, -ús, m senate		n cornú, -ús, n horn
	Singular		Singular		Singular		Singular		Singular		Singular
Nominative	léx	——	iús	——	cívis	——	mare	——	senátus	——	cornú	——
Accusative	légem	–em	iús	——	cívem	–em	mare	——	senátum	–um	cornú	——
Genitive	légis	–is	iúris	–is	cívis	–is	maris	–is	senátús	–ús	cornús	–ús
Dative	légí	–í	iúrí	–í	cíví	–í	marí	–í	senátuí	–uí	cornú	–ú
Ablative	lége	–e	iúre	–e	cíve	–e	marí	–í	senátú	–ú	cornú	–ú
	Plural		Plural		Plural		Plural		Plural		Plural
Nominative- Accusative	légés	–és	iúra	–a	cívés	–és	maria	–ia	senátús	–ús	cornua	–ua
Genitive	légum	–um	iúrum	–um	cívium	–ium	marium	–ium	senátuum	–uum	cornuum	–uum
Dative- Ablative	légibus	–ibus	iúribus	–ibus	cívibus	–ibus	maribus	–ibus	senátibus	–ibus	cornibus	–ibus

The mixed declension ("-rum/-bus")

The fifth declension shares the characteristics of the other two groups:

	Fifth declension
	E-Stem
	mf diés, éí, m day
	Singular
Nominative	diés	——
Accusative	diem	–em
Genitive- Dative	diéí	–éí
Ablative	dié	–é
	Plural
Nominative- Accusative	diés	–és
Genitive	diérum	–érum
Dative- Ablative	diébus	–ébus