Sōng means releasing, jǐn means tensing. In Yiquan these are not two states to choose between but a pair that keeps turning into each other. Slack will not do, nor will stiff — what is sought is the space between, and a mobile one.
The image of the ball comes from the founder’s family: with too much force it bursts, with too little it flies off. The hands should hold it so that a light wind does not carry it away — not squeezing, not letting go. That is Song Jin in miniature: both sides are present at once, neither may prevail.
Letting go without collapsing. Released is what can respond at any moment. The opposite of song is not tension but stiffness.
Gathering without becoming hard. Tensed is what can hold force. The opposite of jin is not relaxation but slackness.
The jin in Song Jin is jǐn, “taut, tensed” — not jìn, the shaped force contained in Ting Jin or Mo Jin. Same romanisation, different word.
Yao Chengguang traces the image back to his father Yao Zongxun: the flag looks taut and still, yet it trembles in small, very fast waves, as if the wind wanted to tear it apart. From afar nothing seems to move — on contact it explodes. Song Jin is therefore not a mixture of some looseness and some tension, but a fast alternation between the two.
“Inside, alternating between loose and tense. Slack will not do; too tense cannot change.”
— Yao Chengguang on listening to force in TuishouWhoever exerts themselves usually tenses at the top — shoulders, arms, chest — and stays loose below. A medically oriented system of standing practice describes the stance as the exact reversal. Switch between the two.
In the stance: released above, tensed below; the form loose, the mind alert. The last row is the most important — tension sits first in the intent, not in the muscle.
Yao Chengguang describes the alternation in stance and Shili as the same in essence and different only in form. The tension needs only a little more force than ordinary looseness: a matter of coordination, not of effort.
In Zhan Zhuang the alternation happens on the spot. Nothing can be seen from outside; inside it goes back and forth between releasing and tensing.
Release, tense, release — in one single, unbroken movement from starting to end position. At the end, check briefly whether the wholeness is still there. Without this order there is a risk of “blind changes”.
The path breaks up into many points, with a change at each — like gears, with a faint grinding. From outside slow and seemingly powerless, inside a fine vibration.
“You want to move and at the same time you stop; you want to stop and yet you move.”
— Yao Chengguang, theory of ShiliSong Jin is not an exercise of its own but a quality contained in every stage — and tested differently at each.
When probing for force in the stance, the movement with the idea of resistance is the tensed phase, the pause the released one — even though one stays loose in both.
The point of contact is constantly moving. Whoever turns stiff or slack changes badly at that point and loses it. Only one who can change hears the other’s force.
Releasing force is the alternation in its shortest form: from looseness to tension in an instant, released again at once. The aim is a force that is sudden and at the same time continuous.
Song Jin presupposes the releasing that Yiquan calls Fang Song, but goes beyond it: Fang Song is the ability to loosen without going slack; Song Jin is the consciously guided alternation between releasing and tensing. What is described is body mechanics, not metaphysics — even if the pair behaves like yin and yang.