Expertlatin
Latin declension is the set of patterns according to which Latin words are declined—that is, have their endings altered to show grammatical case, number and gender. Nouns, pronouns, and adjectives are declined (verbs are conjugated), and a given pattern is called a declension.
How do you know what declension to use in Latin?
It is actually super easy to identify the declension of a Latin noun. You look at the noun's genitive singular form and see what ending it has. This ending tells you which declension it belongs to.
Why are there 5 declensions in Latin?
Diēs, for example, became the only masculine in the fifth-declension, while domus can't decide whether it's second or fourth. But almost no nouns actually remained "irregular"; Latin was very good at forcing them into these five categories. And thus, the variety of PIE nouns became Latin's five-declension system.
