The two BIG buckets for classes are martial (hit stuff with weapons) and casters (hit stuff with magic),some may add half-caster (hit stuff with weapons AND magic). We're going to break out some of the classes from the martial bucket into their own expert/skill bucket.
These classes focus on being the best at a particular skill, tool, craft, as opposed to Attack, Magic, Attack AND Magic. Martial, Skill, Half Cast, Full Cast. 4 buckets. Full Cast has 4 entries (arcane, divine, primal, and psionics). 4x4=16 so we need many more classes. ...yea..