Thirteen Important Points in Taijiquan

Sink the shoulders and drop the elbows; contain the chest and pull up the back; the qi sinks to dantian; an intangible energy lifts up the crown of the head; loosen the waist and kua; distinguish empty and full; upper and lower follow one another; use mind intent, not strength; inner and outer are united; intention and qi interact; seek stillness in movement; movement and stillness are united; and proceed evenly from posture to posture. These thirteen points must be attended to in each and every movement. One cannot neglect the concept of these thirteen points within any of the postures. I hope that students will be cautiously attentative, and test and verify these in their practise.

Yang Chengfu (1883-1936) The Essence and Applications of Taijiquan translated by Louis Swaim
ISBN 1556435452

p. 12-13