In Tai Chi Chuan, the foundation built by solo practice (jibengong, form, standing, dingzhi etc.) is evident and most practitioners who have studied the art for some time can easily say what it is. In a simple way, I could say that the foundation in Tai Chi is about whole body integration and coordination, building stability and balance (develop root), learning how to move from the core and centerline, and maybe a few other things worth mentioning.
However, there’s another aspect, foundation of Tai Chi as a martial art. I believe that people in general are not really aware about this or that they don’t really understand that the Martial Art has another side that can only be developed by partner practice. Push hands is fine, this often follow form practice. Most beginners start practicing simple push hands exercises early as it should be. And then we have techniques and methods as defense, parrying, attacking, punching, pushing, qinna, takedowns and throwing. But the practice in itself is not the foundation. You don’t build this foundation just by practicing with a partner if you are not aware of what you should focus on and try to develop.
First, even when practicing push hands or other combat drills and exercises, you should always carry with you and keep the integrity of the foundation you try to build in your solo practice, th whole body integration and coordination, balance (root), how to move from the core and centerline, etc. One aspect of partner practice is to put your “solo foundation” to the test.
The other side is the partner built foundation. Personally, I would sum up the qualities of this foundation as sensitivity, following, mirroring, filling in, as well as getting a sense of angle and distance. From this, there are some skills or jins developed, in Tai Chi Chuan expressed as tingjin, listening skill and dongjin, understanding skill (not to be confused with dong = “moving”). However, you don’t need to understand the names of the jins or care about them. These are qualities developed from the partner foundations practice. When you practice with a partner, always mind the the Tai Chi mechanics of body movement. But also be light, mind your sensitivity, follow with utmost precision, be always aware about the space and distance between you and your partner and experiment with angle.
In Tai Chi Chuan, looking at a “technique” as an absolute method is wrong. A technique or combat drill is there for you to practice and build your foundation. Regardless if you practice to intercept and punch, go in for a takedown or do a subtle joint manipulation, never think about it as a technique. These are all ways for you to see if you can relax, continue to breath deeply, practice on how to move from your center, test your balance and alignment and to teach you from what distance and angle you can utilize your body in the best way and achieve the best leverage.
If you always mind the details, then eventually acting from the correct body method will become second nature. And then the skills will be developed naturally. Never reach out too far or you’ll forget what is near. In solo practice, approach everything you do in your practice methodically and put meticulous attention to the small details of body movement and mechanics. In partner practice, keep the same approach and attitude, but also be aware of, and put special attention on, the aspects that you can only develop from partner practice. This is my own humble opinion and my own humble advice. But it is also something of the best advice I could possibly give a beginner or to someone who is somewhat new to the art of Tai Chi Chuan.