Our tai chi movements utilise three dimensions at all times:

1. Vertical
2. Horizontal
3. Forwards & backwards

Every posture, every movement, is a combination of these three dimensions.
It has to be. It is the physics. Width, height, length.

Certain body parts enable us to use three dimensions:

1. up & down, using hand and back
2. side-to-side, using the waist, hips and legs
3. movement between the feet

 Pick any tai chi exercise or movement and consider it in light of this.

Pushing is the action of moving something using the application of force.
Force requires something to push off; this is called resistance.
Resistance is the opposing force.

Tai chi never uses force against force, so it can only be applied when there is very little resistance.
We only ever apply 4 ounces of pressure.