If you wish to delve deeply into the subject of the first Latin declension, see Wikipedia.
Si post fata venit gloria, non propero.
If glory comes after death, I'm in no hurry.[1]
The First Declension
The first declension nouns are all feminine nouns. As with all the declensions, the ending of the noun (its inflection) changes depending on case and number. Using the word aqua (water) as an example:
| Case | Singular | Plural |
|---|---|---|
| Nom | aqua | aquae |
| Gen | aquae | aquārum |
| Dat | aquae | aquīs |
| Acc | aquam | aquās |
| Abl | aquā | aquīs |
Every noun with a nominative singular ending in -a and a genitive singular ending in -ae is a first declension noun. Merely specifying how the nominative singular ends is not enough to identify which declension a noun belongs to, which is why the dictionary entry for a noun will always give both. The dictionary entry for the above word would be aqua, -ae.
Generalizing, the endings for the first declension are:
| Case | Singular | Plural |
|---|---|---|
| Nom | -a | -ae |
| Gen | -ae | -ārum |
| Dat | -ae | -īs |
| Acc | -am | -ās |
| Abl | -ā | -īs |
All the endings:  | ||
It is important to memorize and be able to retrieve at will the ending for any declension, case, and number. Any technique for memorization that works for you is fine. One technique is to listen to the endings spoken in order (first all the singular, then all the plural), and listen to them over and over until you can virtually hear the voice in your head. Every time you have a spare moment -- in the bathroom, in the shower, when you wake up, when you go to sleep -- try to hear the voice and repeat the endings. Then pick a random case and try to retrieve its singular and plural endings. This will help you select the correct ending for a given case and number at will.
Notes
- ↑ Martial, book V epigram X.