Second major point: the arms and hands. In Cheng’s form and push hands, we virtually never see the use of any force whatsoever, nor even the change of the hand/wrist configuration to issue power,
as almost all other styles (including most Yang family) do. After watching Cheng repeatedly neutralize and uproot students—most of them considerably larger and heavier than he—truly without using force in his hands or arms, I have come to understand the method, the physiological science if you will, of what he is doing:

We are primates (descendants of tree-swingers), and we also live “civilized” lives in which the majority of our actions are accomplished by neurological messages sent to the muscles of the hands and arms. We open a door, we answer the phone, we hammer a nail, we wash a dish, we type on a computer, we write, we draw, drive a car, give a massage—all primarily events occurring through the neuromuscular circuits of the upper body, primarily arms and hands/fingers. However, when playing push hands, for example, the impulse to respond to a push—or take make one of your own, is quite weak and ineffectual when made from the arms/upper body alone. We try to use the whole body, center the movements in the waist, etc, but we fail because the circuitry to the arms and hands is so predominant, that we are never really integrated, rooted, effortless, etc as Tai Chi desires us to be. Cheng Man Ching, by making his arms and hands completely neutral, soft, empty, etc, forces
the impulse to respond top an attack—or to make one’s own offensive move—to be distributed neurologically to the rest of the body—ie, the legs and trunk, producing movement that is, yes, integrated, rooted, and (relatively) effortless. The body in fact, becomes more “intelligent” when the option of using the arms and hands to respond is “taken off the table”. The reason Cheng moves with such ineffable grace, superb coordination, and obvious functional potency is not because he is a great natural athlete, but because he has suffused his entire body with the “intelligence” of the human hand.

Think of the incredible dexterity, speed, changeability, subtlety of the human hands playing a Chopin piano sonata; now imagine an entire body that is imbued with the same qualities. And of course, as with all things Tai Chi, the opposite is also true:the power of an integrated whole body that can lift a boulder from the ground—imagine that power concentrated in the hands. Some version of both these transferences is what occurs when, using Cheng’s method, the arms and hands are kept soft and empty. It is not, as some would have it, a moral or philosophical principle, to use no force (in the arms and hands), but rather a practical, empirical method by which a higher level of functioning can be achieved. A mundane example: have you ever gone to open a refrigerator door, or a window, and because it turned out to be stuck somewhat, you wound up pulling your body out of balance, while the fridge door (or window)remained shut? And conversely, if you try the same door again, but imagine your arm and hand to be quite weak and devoid of strength, so that you have to pull the door with your legs and back, does it not now fly open effortlessly, in the face of your integrated, whole-body power? The “secret” if you will, is giving the “command” to the whole body, and denying the hands/arms the first crack at solving the problem. In Cheng’s Tai Chi, this process is repeated endlessly, both in form, push hands, and sword work—until it becomes natural, the “default” mode of using the body. And the result is mastery.