When it comes to counting, you can find either Cardinal or Ordinal Numbers. Ordinal numbers tell you which order a noun is in, as in, first, second, or third – and so on. Ordinal numbers in Latin function as adjectives and are declined like first and second declension adjectives, so they will change endings to match the number, gender, and case of the noun that they describe.
e.g., Prīma vacca fugiēbat. The first cow was fleeing.
Secundam vaccam cūstōdīmus. We guard the second cow.
Cardinal numbers, on the other hand, say how many there is of something, and mostly are indeclinable adjectives – meaning they don’t change their endings. The only exceptions are the numbers for ūnus (one), duo (two), trēs (three), and multiples of centum (a hundred).
- ūnus is declined almost like a first and second declension adjective, but with some differences in the genitive and dative forms.
- duo is declined irregularly, though you may spot some familiar endings.
- trēs is declined like a third declension adjective.