furrykef wrote:"Num" and "quia" are entirely different, and in fact I'm confused as to why you think they're similar... ^^;
Num = negative question particle. Indicates that the speaker expects an answer of 'no'. "Num id crēdis?" = "You don't believe that, do you?" (The question may or may not be rhetorical.)
"Quia" simply means "because". You will also see "quod" with that meaning, though "quod" has other meanings as well.
furrykef wrote:Ahh... now that makes sense. ^^; I should have caught that, especially since I used to have the same question!
From what I can gather, it has to do with the way the sentences flow together more than anything. "Quia" (and "quod", for that matter) is generally like English "because", and "nam" and (sometimes) "enim" are more like archaic English conjunction "for" ("for he's a jolly good fellow", "for God so loved the world")... unfortunately, it may be a hard distinction to grasp if your native language doesn't make a similar distinction. I'm usually good at explaining things even when other people throw their hands up in despair at trying to explain it, but this has even me at a loss...
EDIT: I'm gonna take a stab at explaining it anyway. I think "quia" and "quod" imply a stronger connection with what was just said. You use them to answer the question "why?" -- sometimes the question is merely implied rather than explicitly asked. In this case, providing the reason is the primary purpose of the sentence. "Nam" and "enim" are used for more incidental information, as if to say, "Oh, by the way, that's because [blah blah blah]".