Latin declension

Latin declension is the set of patterns in the Latin language for how nouns and certain other parts of speech change form according to their grammatical case, number and gender. Words that change form in this manner are said to be declined.
Declension is normally marked by suffixation: attaching different endings to the declined word. For nouns, Latin grammar instruction typically distinguishes five main patterns of endings. The patterns are numbered from first to fifth and subdivided by grammatical gender. The term "declension" can refer either to the overarching phenomenon, or to one of these specific five patterns. For example, nouns that have a genitive singular form that ends in -ae are said to belong to "the first declension".
Adjectives are of two kinds: those like 'good' use first-declension endings for the feminine, and second-declension for masculine and neuter. Other adjectives such as belong to the third declension. There are no fourth- or fifth-declension adjectives.
Pronouns are also of two kinds, the personal pronouns such as 'I' and 'you ', which have their own irregular declension, and the third-person pronouns such as 'this' and 'that' which can generally be used either as pronouns or adjectivally. These latter decline in a similar way to the first and second noun declensions, but there are differences; for example the genitive singular ends in -īus or -ius instead of -ī or -ae and the dative singular ends in -ī.
The cardinal numbers 'one', 'two', and 'three' also have their own declensions. However, numeral adjectives such as 'a pair, two each' decline like ordinary adjectives.
Declension is a specific type of inflection, and is distinguished from other ways that words change form in the Latin language, such as the conjugation of verbs.

Grammatical cases

A complete Latin noun declension includes up to seven grammatical cases: nominative, vocative, accusative, genitive, dative, ablative and locative. The locative is limited to a few nouns: generally names of cities, small islands and a few other words.

Syncretism

Different cases commonly share the same form. The patterns of shared endings vary depending on a noun's grammatical number, gender, and declension class. The following are the most notable patterns of syncretism:

Number-based

The nominative and vocative are always identical in the plural.
The dative, ablative, and locative are always identical in the plural.
Gender-based
For neuter nouns, the nominative, vocative, and accusative cases are always identical. The nominative, vocative, and accusative plural almost always ends in -a.
Declension-based
The vocative and nominative singular are identical for all nouns except non-neuter second declension nouns ending in -us and a few learned borrowings of Greek origin.
The genitive singular is the same as the nominative plural for first-, second-, and fourth-declension non-neuter Latin nouns.
The dative singular is the same as the genitive singular for first- and fifth-declension Latin nouns.
The dative singular is the same as the ablative singular for all second-declension nouns, some third-declension nouns, and some fourth-declension nouns.
The locative singular is identical to the genitive in the 1st and 2nd declensions; to the dative or ablative in the 3rd declension; to the ablative in the 5th declension.
The non-neuter nominative and accusative plural are identical for all nouns of the 4th declension and 5th declension, and for many nouns of the 3rd declension.
Order of cases

The Roman grammarian Aelius Donatus, whose work was used as standard throughout the Middle Ages, placed the cases in this order:
This order was based on the order used by earlier Greek grammarians, with the addition of the ablative, which does not exist in Greek. The names of the cases also were mostly translated from the Greek terms, such as wikt:accusativus#Latin from the Greek wikt:αἰτιατικός.
This traditional order was formerly used in England, such as in The School and University Eton Latin Grammar. That order is still followed in most other European countries. Gildersleeve and Lodge's Latin Grammar also follow this order. More recent Latin grammars published in the United States, such as Allen and Greenough's New Latin Grammar and Wheelock's Latin follow this order except they list the vocative last.
However, in Britain and countries influenced by Britain other than the United States, the Latin cases are usually given in the following order: nominative, vocative, accusative, genitive, dative, ablative. This order was introduced in Benjamin Hall Kennedy's Latin Primer, with the aim of making tables of declensions easier to recite and memorise. It is also used in France and Belgium. In , a song in French by the Belgian singer Jacques Brel, Brel sings the declension of "rosa" as rosa, rosa, rosam, following the British order of cases.

History of cases

had essentially two patterns of endings. One pattern was shared by the first and second declensions, which derived from the Proto-Indo-European thematic declension. The other pattern was used by the third, fourth and fifth declensions, and derived from the athematic PIE declension.

Nouns

Regularly inflected Latin nouns have two principal parts: the nominative singular and the genitive singular. Each declension can be unequivocally identified by the ending of the genitive singular. This ending can be removed from the genitive singular form to find the noun's oblique stem, which is shared between all inflected forms aside from the nominative singular.
Latin declension is commonly taught in terms of attaching different sets of vowel-initial endings to the oblique stem. For example, the first-declension noun vacca 'cow' has the genitive singular vaccae, with the oblique stem vacc-. Its ablative singular can be formed by combining vacc- with the ending -ā, forming vaccā. The second-declension noun taurus 'bull' has the genitive singular taurī, with the oblique stem taur-. Its ablative singular can be formed by combining taur- with the ending -ō, forming taurō.
There are five declensions for Latin nouns:

First declension (''a'' stems)

Nouns of this declension usually end in -a in the nominative singular and are mostly feminine, e.g. and . There is a small class of masculine exceptions generally referring to occupations, e.g. , , , and .
The predominant letter in the ending forms of this declension is a. The nominative singular form consists of the stem and the ending -a, and the genitive singular form is the stem plus -ae.

	Singular	Plural
Nominative, Vocative	-a	-ae
Accusative	-am	-ās
Genitive	-ae	-ārum
Dative	-ae	-īs
Ablative	-ā	-īs
Locative	Gen.	Dat.

The locative endings for the first declension are -ae and -īs, similar to the genitive singular and ablative plural, as in ' 'in war' and ' 'at Athens'.

First declension Greek nouns

The first declension also includes three types of Greek loanwords, derived from Ancient Greek's alpha declension. They are declined irregularly in the singular, but sometimes treated as native Latin nouns, e.g. nominative instead of the original athlētēs. Archaic first declension Greek nouns and adjectives had been formed in exactly the same way as in Latin: nephelēgeréta' Zeus had in classical Greek become nephelēgerét'ēs.
For full paradigm tables and more detailed information, see the Wiktionary appendix First declension.

Second declension (''o'' stems)

The second declension is a large group of nouns consisting of mostly masculine nouns like and and neuter nouns like . There are several small groups of feminine exceptions, including names of gemstones, plants, trees, and some towns and cities: these take the same endings as masculine nouns.
In the nominative singular, most masculine nouns consist of the stem and the ending -us, although some end in -er, which is not necessarily attached to the complete stem. Neuter nouns generally have a nominative singular consisting of the stem and the ending -um. Regardless of gender, every second-declension noun has the ending -ī attached as a suffix to the stem of the noun in the genitive singular form. The predominant letter in the ending forms of this declension is o.
The locative endings for the second declension are -ī and -īs ; "at Corinth", "at Milan", and "at Philippi".

Second-declension ''-ius'' and ''-ium'' nouns

Nouns ending in -ius and -ium have a genitive singular in -ī in earlier Latin, which was regularized to -iī in the later language. Masculine nouns in -ius have a vocative singular in -ī at all stages. These forms in -ī are stressed on the same syllable as the nominative singular, sometimes in violation of the usual Latin stress rule. For example, the genitive and vocative singular Vergilī is pronounced Vergílī, with stress on the penult, even though it is short. In Old Latin, however, the vocative was declined regularly, using -ie instead, e.g. fīlie " son", archaic vocative of fīlius.
There is no contraction of -iī in plural forms and in the locative.
In the older language, nouns ending with -vus, -quus and -vum take o rather than u in the nominative and accusative singular. For example, could be servos, accusative servom.