Tai Chi: finding balance in complementary opposites

The entire article (linked through the title above) was beautifully written, however, the list of the Ten Essential Elements of Tai Chi at the end of the article are what I want to emphasize:

Yang Chen-Fu's Ten Essentials of Tai Chi
(what you should try to emphasize in your practice)

1. Head upright to let the spirit of vitality rise to the top of the head.
2. Hold in the chest and pull up the back
3. Relax the waist (VERY important)
4. Differentiate between insubstantial and substantial (stance).
5. Sink the shoulders and drop the elbows
6. Use intent rather than force
7. Synchronize upper and lower body
8. Harmonize the internal and external
9. Move with continuity
10. Move with tranquility

I had a student ask me: "After the third form (of the Yang 108-movement form, which is broken into three form-sets for teaching), what's left to learn?"

When these 10 elements fall into place in your form practice, you become "transported," and begin to discover what Tai Chi is really all about.