What are kata?What do kata do?
Kata means "shape" or "form". "Pattern" or "paradigm" are also good translations.Kata are said to be the heart of Karate and are often greatly mis-understood. Making geometric patterns in a prescribed order are how kata appear. Sets of moves linked together in combination.Solo kata performance is the norm in Karate, but why do we need kata?
Much can be made of performing kata for competition, in order to win medals. This isn't necessarily a good or bad thing, it's just one way of using kata.
Performing kata as exercise can be useful. It conditions the body when performed with an eye towards athletic excellence. It can also condition the mind. It can help with endurance and with mental rehearsal of combative training. For visualisation to be of any use in self defence however, you need to know what the moves do. That's usually referred to as the bunkai.
Once you know the bunkai you can see that you cannot perform that move with full speed and power on a living partner. That's why you need to perform the kata without one.
A note on language: the word kata is Japanese. In Japanese there are no plural sounds. You work out whether something is plural or singular from the context. That means that you can have one kata or five kata. There are no katas.