Like many other languages, Latin has a part of speech called a preposition. Prepositions in English include to, from, of, in, and about.Because English has no cases, it's easy to figure out how to use them. But Latin is not so lucky.
Most objects of prepositions in Latin take the accusative case, but there are a few that take the ablative.Since there is no real rule for which are ablative and which are accusative, you just have to memorize them.
But that doesn't mean it has to be boring, or even difficult! Thankfully, we have the mnemonic SIDSPACE*.
S - sin(e)
I - in
D - de
S - sub
P - pro
A - ab
C- cum
E- e(x)
But how are we going to remember all that?
Well, there's something you need to know about Sid. He's kinky. SIDSPACE isn't just Sid's Space, it's Sid's Special Space. Sid is very sinful. He's so amorous that he's not going into** someone, he's already in them. And when he does it, he likes to go deep. Surprisingly, he's not a dom, he's a sub**. He's pretty much a pro at what he does. One of his quirks is that he really likes people with abs. They really make him cum. Some people can't take the heat, so Sid has a lot of exes.
Yes. Despite how embarrassing it seems, it actually works. Just don't tell your Latin teachers, and you'll be fine. Maybe they'll even be really impressed at your sudden ability to recall which prepositions are ablative!
*This does not cover all ablative prepositions, rather, the most common ones. There are others like super and prae which you learn later on, but do not fit the mnemonic. However, these are not very common.
**In and Sub can take both the ablative and the accusative, depending on what meaning they have. As suggested in the example for in, when something is going into something else, that something else is accusative. It is only when the something is already in the something else that the something else takes the ablative. Sub works the same way, just for under rather than in.