Latin Adjectives, part 1

Latin adjectives aren't all that difficult if you've got the nouns under control. After all, they have the same three features that nouns have: case, number and gender. And those are the features to focus on. Pay no attention to that declension behind the curtain—to steal a line. The reason some students like to fix on declension matching as well as case, number and gender is that 1st and 2nd declension nouns and adjectives are taught first. They see this:

casae rubrae

Excellent! The adjective has the same ending as the noun. All is good. Well, of course they have the same ending. Case, number and gender are all the same. Since the declension also matches—first declension in the example—the endings are identical. That's the real explanation.

Naturally enough, when a noun and adjective happen to be in the same declension, this will rightly be the situation. Whenever vir (2nd declension) is modified by magnus, -a, -um (1st/2nd declension), we will see identical endings.

viro magno  
viris magnis

Again, all is right with the world. I know what your thinking: what if declension is different? No problem. We still agree in case, number and gender.

manui dextrae

Dative, singular and feminine. The endings are different because manui is 4th declension and dextrae is 1st declension. If you want to say

manui dextrui

you need to remember that only case, number and gender count. Pay no attention to that declension behind the curtain. Next time: 3rd declension adjectives.