[Endoperez]

There are two kinds of limits for spells and items: research requirement, and path requirement. Level 0 items are trinkets, and mostly require level 1 or 2 in a single path. Items from Construction 2 are minor and often only require level 1 in a single path, but some take level 3 (Enormous Cauldron of Broth takes Nature 3), and Soul Contract is very expensive (Blood 6 Fire 1, so 65 slaves and 5 fire gems).

Similarly for your mages, once you have researched level 4 in Evocation, all mages know the spell "Blade Wind". If they have 3 levels in Earth magic, they can cast it. If they have Earth 1, they can't. But if you give them Earth Boots (for +1 to Earth) and make them cast Conjuration spell Summon Earthpower (for +1 to Earth), even mages who only have one innate level in Earth can cast Blade Wind and other E3 spells.

Earth isn't very important for good items, but Earth 3 gives access to Dwarven Hammers which make all further forging 25% cheaper. They are supposedly one of the most important items available, often traded for in multiplayer if your nation can't forge one, and Earth-wielding pretender is a good choice for any single-player games where you want to try your hand at forging items.