Yilu trains the body in a soft way
Erlu trains the techniques in a vigorous way
With both combined, then you know Taijiquan
The main purpose of Yilu is to train the body to open according to the requirements of Taijiquan. The method can be hard or soft, but mainly soft. Being soft is for movements, the body parts cannot be soft. Because the movements are soft and the range is big, the body parts themselves do not change. On the contrary, the body parts can be recombined at ease. You can also take it this way, Yilu training is the process of making a table out of a tree. From tree to table, the wood material itself does not change, but the effect is changed. This kind of change is from the change of structure, not the change of wood itself.
Therefore, the training of Yilu is for changing the body structure. In general, Yilu is to train the body itself.
Erlu Cannon Fist is different. As the body itself is already trained, the structural force is gained, on top of which, we want to add gong. This is accomplished by movements. The basis of Erlu is to not think about body parts themselves, completely forget about them(the body parts are loose, no need to be considered), the focus is on the movements, which have to be done with a lot of power, speed and difficulties, being more strict according to the application requirements of Taijiquan. This is like you are hammering a nail, you don’t think about the nail, no matter how hard it is, you just swing the hammer and hit the nail with power.
At this point, Erlu is to train application techniques, which we spend a lot of time on. This is to train the methods of Taijiquan.
When both of these two elements are in position, you can do Taijiquan!
Originally posted in Chinese by Master Chen Zhonghua on https://www.zhenbudong.cn/archives/91052. Translation-Yuxin Liu