Tai-Chi essential 5 of 10:
沉肩坠肘 (Shoulders with chi)
沉肩坠肘 沉肩者，肩松开下垂也。若不能松垂，两肩端起，则气亦随之而 上，全身皆不得力矣。坠肘者，肘往下松垂之意，肘若悬起，则肩不能沉， 放人不远，近于外家之断劲矣。
My rendition of essential 5: “During form practice, one must be able to feel the movement of one’s loosened shoulder joints, and able to feel the elbows dropping down (pulling the shoulder joints away) and directing such movements of the shoulder joints”. To achieve this one’s shoulders must be loosened first. If one’s shoulders are not loosened, they would be pulled up rather than moved around in the sockets when one’s hands move about. And chi will be misdirected and the whole body will become powerless (even though essential 1 to 4 have been practiced to create the power in the first place). If the elbows are not dropping down and pulling the shoulder joints away, one can’t feel the movement of the shoulder joints and can’t execute a continuous pushing action during pushing hands.
Paul’s additional comment: This essential act should be achieved through loosening one’s shoulder joints. Zhan Zhuang practice can help to loosen one’s shoulder joints. One of my previous post also deals with loosening one’s shoulder joints (check here). Without first loosening one’s shoulder joints, the essential just become empty talk. Through this essential act, power generated by the feet (and perfected by essential 1 to 4) can be carried up to the hand without obstructions. I noticed that some practitioner misinterpreted this essential as only meant to be lowering one’s elbow to protect oneself and not to move one’s shoulder before punching during combat.