Declensions :
Nouns in -a.
They belong to the
1st declension (-a, -ae).
Nouns in -a are mostly feminine, but some of them – when they denote men – can be masculine. Examples: causa, copia, Italia, Gallia, natura, aura, provincia. Masculines : agricola, poeta.
| case | singular | plural |
| nom. voc. | causa | causae |
| gen. | causae | causarum |
| acc. | causam | causas |
| dat. | causae | causis |
| abl. | causa | causis |
Nouns in -um.
They belong to the
second declension (-um, -i). They are neuter nouns, so the rule is applied that nom. acc. voc. have the same form.
| case | singular | plural |
| nom. acc. voc. | castrum | castra |
| gen. | castri | castrorum |
| dat. abl. | castro | castris |
Nouns in -us.
They are in majority masculine, some of them are feminine and neuter. Masculine and feminine nouns in -us belong to the 2nd declension (-us, -i) or to the 4th declension (-us, -us). It is difficult to foresee to which declension a given noun belongs.
Nouns in -us, 2nd declension (-us, -i):
| case | singular | plural |
| nom. | numerus | numeri |
| voc. | numere | numeri |
| acc. | numerum | numeros |
| gen. | numeri | numerorum |
| dat. abl. | numero | numeris |
If the ending is -ius, the vocative is in -i instead of -ie: filius - fili.
Nouns in -us,
4th declension (-us, -us):
| case | singular | plural |
| nom. voc. | exercitus | exercitus |
| acc. | exercitum | exercitus |
| gen. | exercitus | exercitorum |
| dat. | exercitui | exercitibus |
| abl. | exercitu | exercitibus |
Neuter nouns in -us, like tempus or genus, belong to the 3rd declension. Also some feminines in -tus (salus, virtus). They will be covered later.
Nouns in -u.
Nouns in -u are neuter and belong to the
4th declension.
| case | singular | plural |
| nom. acc. voc. | cornu | cornua |
| gen. | cornus | cornuum |
| dat. abl. | cornu | cornibus |
Nouns in -er and noun vir. Nouns in -er most often belong to the 2nd declension, like nouns in -us and -um. Many of them lose -e- in case forms (before all endings). The exceptions are vir (viri), puer (pueri). Exceptions: pater, mater, frater belong to the 3rd declension.
| case | singular | plural |
| nom. voc. | ager | agri |
| acc. | agrum | agros |
| gen. | agri | agrorum |
| dat. abl. | agro | agris |
Nouns in -es and -ies.
Nouns in -es belong either to the
5th or to the
3rd declension. Nouns in -ies belong to the 5th declension (-es, -ei).
| case | singular | plural |
| nom. voc. | dies | dies |
| acc. | diem | dies |
| gen. | diei | dierum |
| dat. | diei | diebus |
| abl. | die | diebus |
The
3rd declension. Most other nouns belong to the 3rd declension. Its characteristical ending is -is in gen.sing., but the form of the noun can change. In dative it's -i, in acc. -em, in abl. -i or -e, in nom.acc. plur. -es, in gen. plur. -um or -ium, in dat.abl. plur. -ibus. In case of neuter nouns, accusative is equal to nominative, and nom. acc. plur. ends in -a or -ia.
What nouns belong to the 3rd declension ? Nouns ending in :
-a (only some neuter nouns of Greek origin) : -a > -atis : poema, poematis
-e : -e > -is : mare, maris
-o : changes into -onis, more rarely into -inis (always in nouns in -tudo) : legio, legionis, Nero, Neronis, imago, imaginis, multitudo, multitudinis
-c (very rare) : lac, lactis
-l : sal, salis, animal, animalis
-en : -en > -inis : flumen, fluminis, nomen, nominis
-er : -er > -ris: pater, patris, mater, frater
-r : honor, honoris
-t : caput, capitis
-x : -x > -cis or -gis : vox, vocis, dux, ducis, rex, regis
There are also nouns in -s:
-as : -as > -atis : civitas, civitatis, aetas, aetatis
-es : nouns in -es are particularly insecure, they can belong also to the 5th declension (res, rei, same: fides, spes) ; they can change -es into -is (nubes, nubis, moles, molis, vates, vatis, caedes, sedes) or into -itis (miles, militis, eques, equitis, same: dives, comes, gurges), -idis (obses, obsidis), or in one case to -edis (pes, pedis) ; nouns in -ies belong to the 5th declension
-is : -is most often > -is
-os : -os > -oris, but the word os changes into oris or ossis according to the meaning
-us : only some neuter nouns belong to the 3rd declension, and then they change -us > -oris or -eris (tempus, temporis, genus, generis), some feminines : salus, salutis, virtus, virtutis
-rs : -rs > -rtis (ars, artis, pars, partis)
-ns : -ns > -ntis
-bs > -bis, -ceps > -cipis (princeps), -ps > -pis (urbs, urbis, ops, opis).
Third declension, masculines and feminines:
| case | singular | plural |
| nom. voc. | legio | legiones |
| acc. | legionem | legiones |
| gen. | legionis | legionum |
| dat. | legioni | legionibus |
| abl. | legione | legionibus |
Third declension, neuter nouns:
| case | singular | plural |
| nom. acc. voc. | corpus | corpora |
| gen. | corporis | corporum |
| dat. | corpori | corporibus |
| abl. | corpore | corporibus |
Ablativus in -i appears always in neuter nouns in -e, -al, -ar (mare, animal). The same nouns have nominativus pluralis in -ia (maria, animalia) and gen.plur. in -ium (marium).
Many nouns have genitivus pluralis in -ium instead of -um. These are: masculines and feminines having -is, -es in nom. sing. changing into -is in gen. plur. (like navis, navis, navium, nubes, nubis, nubium, exceptions are: canis and iuvenes) and having two consonants before genitive ending -is (pars, partis, partium; but pater, mater, frater, parens are exceptions). Also the nouns cor, cordis and os, ossis belong here.