Just last night I was discussing with Alan Yokota about our Shorin-Ryu Karate Kata curriculum. Chibana Sensei felt that Itosu Sensei had too many Kata. In his discussions with Itosu Sensei, it was decided that Chibana Sensei would teach Itosu Sensei's core Kata, with the addition of the Matsumura Patsai, which he had learned from Tawada Sensei. Chibana Sensei trained with Tawada Sensei for three years in order to learn this Kata. The Chibana Chosin Kata curriculum is the orthodox Shuri-te Kata.
In Okinawa many of the old masters used the phrase, "hitotsu no Kata sannen (one Kata, three years)". In other words, to learn a Kata well, one would have to practice a singular Kata for three years. As mentioned Chibana Sensei trained with Tawada Sensei for three years in order to learn the Matsumura Patsai.
Each Kata or Kata series in Okinawa Shorin-Ryu Karate is a complete fighting system in itself. In other words, Okinawa Shorin-Ryu Karate is a mix of many styles. The Naihanchi Kata was the fighting system that Tudi Sakugawa (Teruya Kanga) learned in China. The Kusanku Kata was the fighting system taught by the emissary, Kusanku. The Patsai Kata Sho (Itosu) or Dai (Matsumura) was/were a complete fighting system by itself. The Chinto Kata was the fighting system of a Chinese fighter named Chinto. The Pinan Kata series is a very complete fighting system, which was created by Itosu Ankoh Sensei to teach the young students in the school system.
As far as I am concerned, the strongest complete fighting Kata are our three Kihon Kata, which were created by Chibana Sensei. Ironically, Chibana Sensei developed the Kihon Kata as a lead-in for the rest of the Kata. The Kihon Kata are a combination of very basic techniques, which makes them the strongest of all the Kata.
The Kata is a combination of basic (Kihon) techniques. One could practice each technique individually, without the Kata. Combat involves movement. This is where the Kata comes in. We are now concerned with the transition from one technique to the other. This transition or pressing (osae) involves timing and rhythm (iki no hyoshi [breathing rhythm]). Kumite practice becomes a distraction because a Kata is against multiple attacks and not just one opponent.
The osae for us is the most important aspect of our Kata practice. I have explained that the osae is the closing of distance. I like Goodin Sensei's word best; entry.
Considering all these factors, it is not one Kata for three years nor five years, but rather one Kata for a lifetime.