I am stuck with the same 6 spells and maxed them. Every time I buy a new spell it never shows up on the list to cast. I have mage and priest spells at 9 and 10 but yet I can't get any new spells to work. I have tried to raise int. but nothing. I don't why they don't work. I even maxed those out just in case their was bug where I needed to cast it at certain level of the spell still nothing. My mage is best used for increasing speed now instead of helping fight stronger monsters just like my priest is better at healing, curing, battle rage and shielding then attacking. Why won't new spells work? Am I doing something wrong?
I found the problem. I have played alot of games meaning that when I buy mage or priests spells they automatically go them but not avernum. I have to make sure to click on the correct person before buying. I'm now looking for unlock level 3. I want to get in the ancient crypt. From experience it is always good to level as much as possible before taking on the ending. I'm working on clearing all areas. I need unlock level 3 for some. I think I might have ran across it some time but don't remember where. Does anyone know where I can get unlock level 3?

I've only played Avernum 1-3 (and I'm playing Blades of Avernum at the moment).
If you select a spell in the status screen, the info tells you the minimum skill needed.
You only have to rise the mage/priest skill. Intelligence is unimportant in that regard.