Can a human have over five Forces without being a Soldier?
Yes, but it requires a very dedicated and motivated person who is actively striving for something more than the average, or for something outside of themselves. (For other ways, see the Corporeal Player’s Guide) Just having six Forces does not give the advantages of being a Soldier (such as Symphonic Awareness and the ability to control one’s Essence deliberately), but it does make one prime recruitment material by either side!
