One is external self defense, the other is self defense of the self through internal discipline

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Folding

The folding move involves one entire side of the body; arm, torso, and leg, moving as a unit. In the example shown in the video left side then the right side of the body are folding and unfolding by keeping the other side of the body stationary.  The stationary part provides support, some of the power for the move and grounding. The left side of the body is yang, the right side yin, then it alternates with right sidy yang and left side yin, etc. The Yin-yang Internal Discipline of the Tai Chi junction is at the spine. One can visualize that the spine is a hinge, so each side of the body, like a door, can fold or unfold using that hinge. This is also a half-body move, right side vs. left  This move in Tai Chi Classics is described as "upper and lower body following each other" Another classical description is, "hand follows the foot, elbow follows the knee, and shoulder follows the hip". This is an important example of how to make a move but still keep each side of the body's alignment intact. This move can be achieved only when the turning power comes from the waist and the entire back's muscles. If one uses the upper body power for this move, the lower body will not likely be able to follow the upper body's move. The left foot will likely be lagging behind the move to form a twisted structure on the left side of the body greatly reducing the power of the move. see https://www.facebook.com/classicaltaichijimroach/