IIRC the original rule was that you can't have two classes that both have any spellcasting, doesn't matter whether it's "full" or "half" or "three quarters". Unless you take an archetype that removes spellcasting from one of the classes. So no paladin/sorcerer combos for example, unless you take one of the paladin archetypes with no spellcasting.<br/><br/>But to answer your question:<br/><br/>Full casters can reach spell level 9, e.g. wizard, cleric<br/>Three-quarter casters can reach spell level 6, e.g. bard, inquisitor<br/>Half casters can reach spell level 4, e.g. ranger, paladin