Ah, found it myself.
Someone posted this in the miscellaneous thread in the post, remarkably enough, about Sung in practice.
It is a translation of a video made by the Grand Master, so it helps to read it if you understand that the GM was demonstrating what he was saying as he said it.
The Essential Points were stated above. Next we shall discuss the approach for training. One of the approaches of training is fang song (let loose or relax). From this fundamental approach, we begin our practice.
"Let loose" in everyday life is easy to explain. lt's not so simple in taijiquan training. This is because taijiquan uses the philosophy of yin and yang and is concemed with the transformation and changes in these two concepts.
Fang song is an approach of training. It is a strategy; it is not something tangible. Today there are many practitioners of Yang style taijiquan, and unfortunately many have not fully comprehended the meaning of fang song, and they misinterpret its meaning. This is because song (relax or loosen) and ruan (soft) were put into the same category. Many think that song is ruan. What we consider as song is not ruan. Song requires that the joints and the muscles be intentionally letting loose, and extended. This is loosened up and extended out. Extended. [He illustrates.) It is not ruan. It is not this way nor this way. If it is this way, it will be difficult to express the jin.
By following the idea of -using your mind to relax, you will attain power naturally. You should intentionally let loose. Similarly to what I mentioned in the Ten Essentials-sink the chest and lift the back; sink the shoulder, drop the elbow, settle the wrist, and extend the fingers-it is not necessary to use forceful muscular strength. When you can sink the shoulder, drop the elbow, settle the wrist, and extend the fingers, you will have power without the need to exert forceful muscular strength. You simply let loose-relax and extend. You will have power without the need to exert forceful muscular strength. You will attain power naturally. Without having to think about it, you will have jin.
What is meant by song is not the song that means "slack and soft," it is the song that means loosen and extend."
Now let's discuss the differences between rou (gentle yielding) and ruan (soft). Ruan is generally defined as empty, that is, hollow. Rou, on the other hand, is ductile. For example, when we practice, if we do it this way, it appears hollow (empty). Therefore, the extension is done this way. It should be this way. But not like this. Not this way.
One must be extended. If we extend this way, the blood circulation is smooth and the body is comfortable. In this strike, the body is comfortable and smooth. All these movements are smooth.
When the waist moves, the hips and the torso move, then express to the fingers. This way is smoother.
Everyone should comprehend fully the meaning of fang song, let loose, in practice. One should be loose and extended, not loose and soft. I hope you will pay attention to this during practice. We require this kind of song: loose and extended. Not this one.
Extended, you see. When done this way, it will be more comfortable. "Press" is also very comfortable. But it doesn't matter which posture you are doing, it should all be like this. You should let loose in 'Fist under the Elbow" and in "Repulse Monkey." Extend, settle the palm, lift leg, and step backward. Fast or slow, the principle is the same. When doing it faster it's still the same. Strike forward with speed. We do it slowly, we do it with jin.
lt doesn't matter whether it is -Slant Flying" or "Part The Wild Horse's Mane." Of course the physical movements are not the same. "Slant Flying" requires a large step, to here. 'Part The Wild Horse's Mane" is primarily a ward off, which steps forward. However, they both need the walst movement and both need to be extended.
Power reaches the four extremities of the legs and hands. Doing it this way is more appropriate.
The training approach of fang song is to let loose; once we can distinguish it clearly, that is good.
In rou and ruan, the distinction is this: ruan (soft) is hollow or empty, whereas rou (gentle yielding), is ductile.
Fang song can be explained with the iron and steel analogy. Raw iron is processed under high temperature melting and other processes, then converted into steel. If we compare the raw iron to li, then the high temperature melting (refinement process) is analogous to fang song. High temperature melting turns the raw iron into liquid. lt is then refined until it becomes steel. This refining process is an approach to make steel; likewise,fang song is an approach, a method, analogous to the high temperature melting refinement process, required in turning iron into steel.
We compared localized li (forceful muscular strength) to raw iron. After high temperature melting or refinement processes, the fang song process, it is converted into steel, into what we call jin.
We conclude this topic here.