There are three initiatives (“Sen”). The first concerns the situation, when you attack the opponent from your own side, the second concerns the situation when you are attacked by the opponent and the third when you and your opponent attack each other simultaneously. These are the three initiatives.
When you attack, you should carry it out so that your body is poised to the outside prepared to attack, but at the same time hold both legs and the spirit back inside and neither relaxed nor tensed move the spirit of the opponent. This is Ken-no-sen.
When an attack comes from the opponent, you should take it in hand so that you at first do not worry about your own body, then in the appropriate proximity release your spirit and therewith according to the movement of your opponent seize the initiative.
And when you and your opponent attack simultaneously, you should keep your body upright and straight and with your sword, with your body, with your legs as well as with your spirit seize the initiative. Seizing the initiative is of utmost importance.
Today we still talk about three sen, usually with the titles Sen sen no sen, Sen no sen, and Go no sen. This is to attack your opponent first (at which point is often debated) at the same time but to get in there first, and after he has attacked when we defend and respond. We can get quite complex about this but the meaning has never changed from Musashi’s day.
I attack, we attack, he attacks. Musashi says that when we attack first we should do it from the outside (beyond the kiri-ma, the cutting distance). We hold back our spirit and our legs (our ki and our tai) and from this state of relaxed readiness, we move the spirit of the opponent. In other words, we disrupt his thoughts about attacking, we seize the initiative before he can form his.
This is not a matter of jumping in first, of being fast. If the opponent is in a similar sense of readiness and you jump in to attack at best you are likely to get an ai uchi, a mutual cutting. You must move his spirit first, put him back on his heels so that he can’t respond to your attack.
Sen sen no sen is something we need to look at in our iaido practice. The kendo federation standard kata begin with Mae, and the instruction begins with something like “recognizing that your opponent intends to attack, you draw your sword and cut him across the forehead.” I won’t pretend I looked that up, but it will be close enough. The target is the head, and if you set this up with a partner you will soon see that your opponent has not moved upward from seiza, he has not, in fact, moved much at all. So we have somehow intuited, we have sensed, assumed, that he is about to start attacking and we have cut him across the face? How is this different than murder? Sen sen no sen is not “cut him before he can start to attack” if he isn’t, in fact, in a fight with you at the moment, it’s murder, and if he is in a fight with you, jumping in will trigger his response (he is in go no sen) and you may fail in your attack, or as mentioned, you may simply get an ai uchi.
As Ohmi sensei has said many times, first you kill him, then you swing your sword. First he must be defeated, then you can begin your attack. Move his spirit.
The case where he attacks first (you are on the other side of what we just talked about) is one where you must take his attack in hand, you must defend, so that you don’t worry about your body, your body is safe. Then you can release your spirit at the proper distance and time to take the initiative away from him and strike. Musashi has written about several ways to do this and we will encounter them soon. The general idea is that when attacked you must deal with the attack first, then counterattack. There is no sense here of sutemi, of assuming an ai uchi is to be desired. Musashi was concerned with teaching his students to win, not to die in a costly way.
The final case discussed here is when “we attack”, when both attack together. In this case alone, Musashi tells us we need to maintain our posture and go in with Ki Ken Tai Ichi, we have to attack with our spirit, our sword, and our body so that we seize the initiative. If our opponent falters in his spirit, or his body or shows an opening in his posture or the path of his sword, we will break through and take advantage of it.
Experience is the key here, and there is probably no better practice than honest kendo. Honest in that we aren’t worried about the rules, but we are worried about cutting without being hit at the same time. It’s not uncommon to watch people jump in, twitch their head aside so they are cut on the shoulder while cutting their opponent on the head. That is playing to the rules, but it’s not all that useful “on the street”.
If you don’t do kendo, you need to pay attention to how you practice your kata. There are ways to study sen in kata, but it takes some dedication.