Check out this thread, I think it is more up your field of expertise.

[CEB]

Rogier has asked questions regarding irimi and tenkan and how it may possibly related to sen no sen and go no sen. He asked this in the Karate forum. I believe you folks could add much to this subject matter.

Link to Thread (http://www.e-budo.com/vbulletin/showthread.php?s=&threadid=21428)

[Ian McDonald]

From my experience and personal inclinations, proper irimi is far beyond mere physical entering. It should be a complete physical and psychological destruction (or dissolution) of the opponent's ability and will to attack, whether you hit them or throw them or not. Properly timed irimi will be sen sen no sen, a preemptive strike or just not being there by the time the opponent targets and attacks. This timing is difficult to master. Tenkan is more "in the now" in the sense that the turning or pivoting is in response to directed energy. More like go no sen. With really good irimi, you will rarely. if ever, need large tenkan. Tenkan results from the natural tendancy to generate spirals and curves, (physics/ mechanics) when two forces (or objects) come together. Since two things cannot occupy the same space/time/phase, we can use irimi to enter a vacuum (or displace a particular object in space-time) and tenkan to create one. Study the question of why the concept and technique is always irimi-tenkan, not tenkan-irimi. The answer to that one (he says in his self-deluded arrogance) is how I arrived at the conclusion that irimi is the most fundamental and most important concept in aikido and swordsmanship. :idea: But that could be just semantics. Good luck.