I just found this in today's email from Stanley Pranin's Aikido Journal.
The Founder can be seen applying atemi or “preemptive strikes” right up until the end of his life. But today, atemi have fallen into disuse in aikido. I believe this is due to a misunderstanding of its purpose. Atemi is an action used to preempt uke’s aggressive intent through a distractionary manouever in the form of a strike. The use of atemi is not for the purpose of hitting or “softening up” uke prior to performing a technique. Its role is similar to that of the kiai in that it disrupts uke’s concentration.
Beyond “Sensen no Sen”
A traditional explanation of strategies in a Japanese martial arts context often involves a discussion of three levels of combat initiative: “go no sen,” “sen no sen,” and “sensen no sen.” These strategies are defined as follows: “Go no sen,” meaning “late attack” involves a defensive or counter movement in response to an attack; “sen no sen,” a defensive initiative launched simultaneously with the attack of the opponent; and “sensen no sen,” an initiative launched in anticipation of an attack where the opponent is fully committed to his attack and thus psychologically beyond the point of no return. The latter strategy is generally considered to be the highest level in the classical martial arts scenario.
Good quote. I should clairify my mentioning of deai and sen sen no sen earlier now that you psted this. In aiki ninjutsu we use all these concepts but name them differently in some cases. Sen no sen as described above is the Banzenkan's conception of deai, it has a defferent name so as not to confuse students between sen no sen and sen sen no sen. Sen sen no sen for us is exactly as described above. Go no sen is different for us however. While we understand the concept of go no sen as the response to the physical attack, we refer to go no sen as manipulation of of the opponent's sen sen no sen. For us, go no sen requires us to move to a position where we bait the attacker, he then makes the commitment to the attack and we move to a superior position after the attack is decided upon but before it is thrown. It gives one the feeling of fight a ghost in my opinion. You know there is something there so you attack it, but it doesn't connect. It leaves one feeling stupified.
Another way we illustrate the point is deai (or sen no sen) is like going to a party and getting there right on time. Sen sen no sen, is getting to the party early and they are still setting up decorations and are surprised to see you there. Go no sen (in the Banzenkan) is giving directions to the party but purposefully giving the wrong address, so the guy shows up on time (attacks when he realistically should), but goes to the wrong place (attacks a target that really doesn't exist anymore).
Hopefully I made some sense to anyone who cares to read my poorly worded explanations.