The 13 Postures is a short set of movement which introduces the core movements and ideas of Tai Chi Chuan. Though simpler than the Open Hand Form (First Duan, etc…) it encapsulates many core ideas of both Tai Chi and Taoism and is worthy of much study.
The 13 Postures are split into three segments, each repeated four times in four directions. The first two segments are directed towards the cardinal directions (South, East, North, West). The third segment is directed towards the diagonals.
Taken together, the three segments point towards the eight points of the compass, but more importantly at the eight points of the Bagua, the symbol of the I Ching. These eight points (marked by a trigram) represent the eight permutation of Yin and Yang energy.