Initiate, Respond, Meet (sen no sen, go no sen, and tai no sen)
These are three, midlevel Japanese training principles. They are meant to encourage the practitioner to think through their art and be aware of the various situations one might encounter. It should be noted that a variety of martial arts use each of these terms differently.
Sen no sen means to take the initiative. Most practitioners think of this as to attack and in fact it can be just that. Once you know the attacker is coming at you and you cannot talk your way out of it – attack. Be aggressive and yet have a calm spirit. This could be a situation where there is no escape; your attacker has assumed some fighting stance and is moving toward you to attack. Sen no sen dictates that you need not wait for them to actually throw the first punch, but you may take the initiative by striking or grappling. It can also mean attacking the attack – for example attacking the fist coming at you with your elbow in order to destroy it.
Go no sen means to respond to the attack. This is the generally preferred feeling of self-defense. Use the attacker’s energy against them. Allow the person to commit and take advantage of their weakness. Use the attack as a means to defeat the attack itself.
Tai no sen means to mutually attack. As your opponent attacks, you attack. In times when dueling with swords was common, tai no sen was used when your opponent was stronger, thus you might seek a mutual slaying. Today, tai no sen is more of a feeling of moving through your opponent as they attack.
These three thoughts on strategy are to make the practitioner aware of how the tools can be used. Keep in mind this is just a stepping stone along the way, and more advanced heiho will take their place.