The taste of true Taijiquan from Yang Chen-fu
By Chen Wei-Ming, Shanghai, 1927
Extraction from "The collection of Chen Wei-ming's Taijiquan writings."
Second edition published in China, 1995 by People's Athletic Education.
From page 159.

Yang Chen-Fu said: "One must distinguish the pure from the motley. Many practice taiji nowadays but it is not the real taiji. The real has a different taste, and is easily distinguished. With real taiji, your arm is like iron wrapped with cotton. It is soft and yet feels heavy to someone trying to support it. You can feel this in push-hands practice. When you touch an opponent, your hands are soft and light but he cannot get rid of them. When you attack, it is like a bullet penetrating cleanly and sharply (gan cui), yet without using any force. When he is pushed ten feet away, he feels a little movement, but no strength and no pain. In touching him, you don't grab him. Instead you lightly adhere to him so that he can't escape. Soon his two arms become so sore he can't stand it. This is real taiji. If you use force, you may move him. But it will not be clean and sharp. If he tries to use force to hold or control you, it is like trying to catch the wind or shadows. Everywhere is EMPTY. It can be likened to walking on gourds on the water. You cannot get to where the substantial is. Put simply, the real taiji is marvelous."