Kiai, "attacking" is the counterpart of aiki, "receiving". (Actually kiai means "the meeting of the ki's, but in practice, in the dojo it is attacking.) In aikido, kiai is used when force is needed, such as in jo waza, where you strike with the stick or block a strike. It is not separate from the strike, but a part of it. The sound will ensure you of the your own power to strike. A loud shout will perplex and distract the uke, so that if he is an opponent, he will fear your self-confidence. A loud kiai can actually prevent an unskilled and uncertain opponent from punching you, so that scuffling is not even necessary. Surprisingly many will stop and think for three to five seconds, and then decide not to attack. When you have trained for a long time, kiai comes automagically. You need not to always shout: a thought kiai may be just as effective. Then again, it won't have the shocking effect.
The sound "kiai" itself is not a good word, because it is formed mostly in the mouth. The kiai is best, when its sounds resonate in the belly: ai, ei, haa, etc. You can imagine how to moo like a cow, deep from the belly, so that you feel how the sound makes your diaphragm, sternum and abdomen vibrate. Then shorten the sound and make it louder, but do not use the throat! Use your upper abdomen!
The sound should not come from the throat, such as "EEEK!", or from the mouth. It should not contain glottal stops, like the "k" sound. The RReal RRolled R, the hissing S and the breathing sounds F and H are good consonants in a kiai, because they don't require closing or moving the lips, so that the sound can go freely through the mouth.
Here are some examples of kiai shouts. (Pronounce phonetically, not in an English way!)
- HAI - sounds like Gypsy...
- EI - has a higher pitch than HAI, but nevertheless, the pitch of I is quite low. Ei is "no" in Finnish.
- SEIS and EI - seis means "stop" in Finnish, "ie" means "no" in Japanese.
- HAA - very loud, but may sound stupid if you don't put all your strenght into it.
- SAA - the same as the previous. Expand it to saatana to make it a Finnish swearword.
- PERKELE - What this loses to the P and the K, it gains in its meaning. It looks like these swearwords were designed for shouting them hard.
Kiai is projection.
Special thanks to: gn0sis, isogolem