Sen Principle

1. Go no Sen: Countering after the attack. This is the “typical” scenario found in early Senjutsu training where an attack is delivered by tori and uke executes a block and counter technique.
2. Tai no Sen: This is where uke delivers a countering technique simultaneously with tori‘s attack. This timing is seen in the first techniques of yakusoku kumite like Nijushiho Waza and Sankakutobi Shodan Ichi.
3. Sen no Sen: This is a strike that is timed to land before tori‘s attack can reach the mark. Sen no Sen is based on the scenario that tori commits to an attack, but uke manages to get in faster.

There is a fourth type of timing, called Sen Sen no Sen (or sometimes simply Sen), which is more of a preemptive strike. Sen Sen no Sen is a timing used when there is no question that violence is imminent, and a Senjutsukā chooses to strike first to bring the situation to a quick close.