Latin Declensions: Why the Dictionary Gives You Two Forms of Every Noun
Open any Latin dictionary and every noun comes with a passenger:
, - king
, - body
, - land
The second word is the genitive singular, and it is not there for completeness. It is there because without it you cannot decline the noun at all.
What the genitive tells you
Two things, and both are load-bearing.
First, the declension family. The ending of the genitive is a label:
| Genitive ends | Declension | Example |
|---|---|---|
-ae | first | terra, terrae |
-i | second | dominus, domini |
-is | third | rex, regis |
-us | fourth | manus, manus |
- | fifth | dies, di |
Knowing the family tells you every ending the noun will take, for all six cases and both numbers.
Second, and more urgently, the stem. Strip the genitive ending and what is left is what every other form is built on:
| Nominative | Genitive | Stem |
|---|---|---|
| regis | reg- | |
| corporis | corpor- | |
| nominis | nomin- | |
| itineris | itiner- | |
| hominis | homin- | |
| partis | part- |
Look at that table properly, because it is the entire argument. You could not have guessed a single one of those stems from the nominative. becomes itiner-. becomes corpor-. Nothing in the citation form warns you.
This is why "learn the genitive with the noun" is the most repeated piece of advice in Latin teaching, and why it is right. A noun learned without its genitive is a noun you can recognise and cannot use.
The first two declensions
These are the friendly ones, and between them they hold a great many everyday nouns.
First declension, genitive -ae, overwhelmingly feminine. , , , , , in this course:
| Case | Singular | Plural |
|---|---|---|
| Nominative | ||
| Accusative | ||
| Genitive | ||
| Dative | ||
| Ablative |
Second declension, genitive -i, mostly masculine in -us or neuter in -um. , , , , , , , :
| Case | Singular | Plural |
|---|---|---|
| Nominative | ||
| Accusative | ||
| Genitive | ||
| Dative | ||
| Ablative |
Neuters in -um differ in one respect that applies to every neuter noun in Latin: the nominative and accusative are always identical, and in the plural both end -a. is both war as a subject and war as an object; is wars either way. That rule saves you a great deal of memorisation and costs you the ability to tell subject from object on a neuter noun, which context has to settle.
The third declension, and why it dominates
Genitive -is. It is the largest declension and it holds a strikingly high share of the most frequent nouns in the language. From this course alone: , , , , , , , , , , , , , , , , , , , .
That is a third of the nouns you have met.
Its endings, once you have the stem:
| Case | Singular | Plural |
|---|---|---|
| Nominative | reg | |
| Accusative | regem | reg |
| Genitive | regis | regum |
| Dative | regi | regibus |
| Ablative | rege | regibus |
Those endings are perfectly regular. All the difficulty of the third declension is in the nominative singular, which is a law unto itself, and all of that difficulty disappears the moment you know the genitive.
Apply it to , , stem corpor-, and neuter:
corpus, corpus, corporis, corpori, corpore - and in the plural corpora, corpora, corporum, corporibus, corporibus.
Same endings, with the neuter rule about nominative and accusative applied.
The fourth and fifth
Small, and worth knowing mainly because a few very common words live there.
Fourth, genitive -us: (hand), (house). The -u- runs through the paradigm: , , , , .
Fifth, genitive -: dies (day), (thing). Tiny family, enormous frequency - is rank 48 in this course and dies is 55, so you cannot avoid them. , , , , .
Adjectives do not have to match the family
A common early confusion, worth clearing up.
An adjective agrees with its noun in case, number and gender. It does not have to belong to the same declension, and often does not:
- a great king
- of a great king
- a great king (as object)
is using second-declension endings and is using third-declension ones. They look nothing like each other and they are agreeing perfectly, because agreement is about the grammatical categories, not about the sound.
Once you stop expecting adjectives to rhyme with their nouns, a great deal of Latin becomes readable.
What to take away
- Learn the genitive with the noun, from day one, always.
- The genitive's ending names the declension; its stem is what everything else is built from.
- The third declension is the biggest, holds the most frequent nouns, and is only hard in the nominative singular.
- Neuter nouns always have nominative equal to accusative, and
-ain the plural. - Adjectives agree in case, number and gender, not in declension.
Next: what Latin does with the freedom that all these endings buy it.