adjective than of the noun; for each of the above adjectives has three forms of the Nominative Case:
| -us | -a | -um |
| (omitted in some adjectives like ‘asper’) |
Similarly we may arrange nouns in three classes:
| Nouns which take adjectives in -us (or those like ‘asper’) | Nouns which take adjectives in -a | Nouns which take adjectives in -um |
| numerus | audācia | castellum |
| nummus | casa | velum |
| patruus | specula | oppidum |
| vir* | amita | etc. |
| liber* | fortūna | |
| etc. | etc. |
- Note that in these cases the ending of the noun is not the same as that of the adjective which goes with it.
To these three classes of nouns it is convenient to give names, nouns of the first class are called masculine, those of the second class are called feminine, those of the third class are called neuter. And the forms of the adjective taken by the different classes of nouns are called by the same names.
In order to know to which class a noun belongs (and therefore which form of the adjective it takes), observe the following rules:-
Nouns of the 1st Declension are feminine, except those denoting male persons, which are masculine: thus insula, casa, ōra, amita, are feminine; agricola, nauta, poēta, incola, are masculine.
Nouns of the 2nd Declension ending in us or r are masculine: e.g. numerus, scopulus, patruus, liber, vir. Some exceptions will be found later.
Nouns of the 2nd Declension ending in um are neuter.
