I don't know if what I'm going to ask about counts as spoilers, but here it is.

Since I'm pretty far into the game and haven't found all that many spell scrolls, am I to assume that you HAVE to experiment to get most other spells? I don't know if the game will eventually hand you a scroll for EVERY spell in the game.

I can sort of see how you could intuit new spells. Put two (or more) related symbols together to get a result (poison + shield = poison shield. fire + shield = fire shield). I've tried experimenting quite a lot under this concept, but am really having no luck, all the same.

There aren't a particularly large number of spells to learn- only four for each type of magic (well, 5 for air), plus light and darkness spells. The types of spells are also similar between the different elemental types (short range damage, long range damage, arrow enchant, elemental shield), plus the rune combinations for each type of spell are similar enough that if you've found a spell scroll for one spell then you can typically intuit what the runes will be for the corresponding spell of a different element type.

That said, I also remember coming across spell scrolls for almost every spell in the game, although some of them were hidden and others showed up pretty late in the game.