Anyone who's trained long enough to become familiar with even a single kata should be aware of their imaginary opponents: the 8 attackers surrounding you, pressing on you from all sides. You've been taught (hopefully) to see them clearly in your mind's eye. "You gotta smell the garlic on their breath!" O'Sensei Kim used to say. These 8 opponents are all bigger, faster, and stronger than you. How can you possibly defeat 8 fearsome attackers, all of whom are physically superior to you? That is the challenge of the kata. But the only way to gain the benefits of meeting that challenge is to develop your imagination, your ability to visualize those opponents, and to translate those images into feelings and movement in your body.
Wow, imagination? Feelings? Visualization? That sounds hard. Or soft and fluffy. Or both. Some people would rather just spar or do self-defense with a live opponent. Ok, no problem! But guess what? You still need your imaginary opponent to train properly!
Your partner as imaginary opponent
So what is this imaginary opponent fellow? Whenever you face your training partner, you must imagine that she is encased in a shell, as if their body is bigger than it actually is. (For me, that shell is soft and foamy, making my partner look like the Stay Puft Marshmallow Man from Ghost Busters). If you are a beginner, the shell should be 6" thick. As you advance, the shell can shrink down to 2". This is your imaginary opponent superimposed on your training partner's body.Let's look at the benefits of visualizing your partner's imaginary body.
Safety margin
When training in kata, it's pretty hard to get injured (and if you do, it's usually your own fault). But training with a live partner is inherently risky. The harder and faster you train, the riskier it becomes. Even a small mistake can have painful consequences. When you picture your target being 6" away from your partner, you have a built-in safety margin. Even if someone zigs when they should have zagged, your chance of accidentally hitting your partner is greatly reduced.Don't practice perfect error
Some people try to avoid injuring their partner by stopping their punches or kicks before they actually land, or they connect but don't use full power. Some schools allow strong blows but not to the body's vital points. But there are problems with both of these approaches.
Similarly, if you practice clobbering each other, but only allow striking to non-vital targets, or use padded protective gear, you are playing by rules that don't exist in the street. That's fine for sport karate, but that is not the intent of the martial arts. And even with armor, injuries are all but assured, because the emphasis is on power, not control.
Attacking the imaginary body is NOT pulling your punch
When you attack your opponent, you attack their imaginary body. Your punch or kick or strike must reach proper distance on the surface of that body and then penetrate it. You can then execute the technique properly without pulling it, or consciously missing. You can target vital points like the eyes, throat, or groin with safety.As a beginner, you should start training slowly and softly, letting your body get used to the movement before applying speed and power. Trying too hard too early only serves to perfect error again. Even going softly and slowly, though, you should see your partner's imaginary body. As you progress, you can pick up the speed, striking the imaginary body with greater power, but always with precision. Once your control warrants it, you can start reducing the size of your opponent's shell but always leaving that safety margin of 2".