In the last Wizardry post, I said: “Wizards, lords and samurai gain spells a lot slower than the pure clerics and mages. Wizards gain spells at the same rate as mages and clerics, but the spell levels are divided between the two types making them weaker but more diverse casters. Lords and samurai gain about half the spells of the two pure casters.”
Now that I have played for a bit more, I noticed the actual rate of spell learning.
Mages and Clerics earn one spell at first level and then gain an additional spell every two levels. The progression is 1st, 3rd, 5th, 7th, etc. Roughly, your mage and clerics will have spell levels equal to their level minus one, divided by two. There is a limit of 9 spells available per level.
Wizards gain spells much slower. They gain 1 mage spell at first level and the next spell four levels later. Fun. Cleric spells start at level four and progress at every four levels. This causes you to alternate between mage and clerical spells.
Samurai and Lords gain spells at fourth level, then receive an additional spell every three levels. Lords gain clerical spells while Samurai use mage spells.