When one is defining the Internal Martial Arts they are, of course, speaking of Tai Chi Chuan, Pa Kua Chang, and Hsing i. These arts are considered soft, and they are designed to build chi power. Interestingly, while there is similarity, there must be difference, and the differences can better be understood by examining the specific geometries of each fighting discipline.
Then there is Pa Kua Chang, which is a circular art in which chi power is said to spiral through the limbs and torso.
Last is Hsing i, which is more straightforward, developing the soft, internal power fist.
Now, Tai Chi doesn’t go anywhere. One deals with an attacker with subtle motions, not giving way, but rather redirecting force, then utilizing one’s own power.
Pa Kua goes in circles, which is a lateral motion.
Hsing i comes straightforward, more of an aggressive attacking sort of art.
The point here is that Tai Chi is the point on the ground, Pa Kua, though circular, describes sideways motion, and Hsing i creates forward and back motion.
Thus the three geometries create plus, or a cross.
While this is not mystical, it does tend to create three methods of combat strategy which, when put together, create a wholistic fighting method.
If the attack is delivered with irresistible force, the tai chi student can shift to pa kua and move aside.
If the attack is not aggressive enough, one can shift to using i and mount a quick but penetrating attack.
Thus, fight or flight, slip or shift, the student who knows all three arts will have much more combat potential than the fellow who doesn’t. And that is the summation, be it a sketch it should still be handy in the overall viewpoint, of the three geometries of the Internal Martial Arts.