Zach Hudson wrote:
Does anybody know (or have a guess at) why O'Sensei made the jo and bokken the primary weapons used in Aikido. Why not any of the many other kobudo weapons?
One answer is that O-Sensei didn't make these weapons the primary weapons of Aikido, later practitioners did. O-Sensei I am sure felt that sword work was core to understanding Budo which would put him in agreement with most Japanese martial artists. But after sword it was really spear in it's many variations that interested him. He avidly practiced Jukendo, used the Bo extensively and even gave separate rank in its use (ie Hikitsuchi Sensei), used jo in demonstrations and for teaching, and there are a number of well known pictures of him using a Boar Spear.
Why he felt that these weapons were important for Aikido students is due to the nature of technique and its relationship to hand technbique. Basically, sword is about cutting or slicing, (although you can certainly thrust) and relates closely to the turning body movements (Ura) of Aikido and the circular cutting movements of the throwing techniques. Spear relates most closely to the entering movements (omote) and the extension movements directly to the center of the partner (including atemi). While each weapon expresses these principles in a slightly different way and has its own "personality" the principles of Entering and Turning are really contained in both weapons as they are not separate principles anyway.