This theory was orginally a single concept without clear differentiation. It was recorded in the Dai Family Xin Yi Quan 戴氏心意拳, where each time one trained a fist, one had to first practice it several times with a soft jin, then one would do a closing movement and then practice it a few times with a hard jin. The intention was to first practice slowly, and ensure that the movments were accurate, and to completely use the yin energy, co-ordinating the movement between hand and feet. Through repeated practice one would collect the jin in the body, accumulate a ball of Qi and issue it with power and sound with an integrated and explosive force, in a complete movement. Hebei Xingyiquan inherited the above method, and took a more direct approach, where one had to first learn the hard jin, so that one would achieve power, and could apply it quickly. Once one had mastered the fierce and hard way of practice, then they would begin to repeatedly train the An jin and Hua Jin. The practice method of the three jin are mainly used in the five element fists, with each fist practiced in three ways, first one would master the hard movement so that they can face the enemy, then one would begin to practice sets, and after that one would go back to the beginning to train An jin. When one was proficient, one would train the 12 Forms 十二形 before finally training the Five Elements Hua Jin. The differences and training methods of the three jin are listed below: Ming jin: Hard Jin, long distance, extension, stepping hard into the front foot, fierce attacks, arm strength. This is the power of metal, and explodes forward, without thinking of retreat. Just like stated in the Sword Classic of Yu Dayou : " Every step moves forward, unmatched under heaven" 俞大猷劍經所謂：「步步前進，天下無敵。」The Boxing Classic states, "Rushing up and rushing down with a tiger posture, fighting hard, entering hard without blocking." 拳訣謂：「搶上搶下勢如虎，硬打硬進無遮攔。」Ming jin requires one to first train the 64 gong 六合四稍功, the three centers (hearts) need to be solid 三心要實 and the Qi needs to sink into the Dantian. The body needs to ready the five bows, and train so that one is stable and low, hard and fierce, one needs to have great courage and the hunyuan power infuses the whole body, which has the effect of increasing power and speed, and is stable and accurate. When striking one is able to knock the opponent back several feet, like "hanging a picture on a wall" or breaking the wall with a step. The classics state, let one, "build one's foundation, strengthen one's body, the bones and body become solid like a rock of iron, and the form and energy field are imposing like the Tai mountain. 拳經謂：使人「築其基，壯其體，骨體堅如鐵石，而形式氣質，威嚴狀似泰山」。This is the foundational practice for changing the bones and tranforming the Jing into Qi. An Jin: Soft jin, short jin, braking feet 剎車腳, blocking hand 窒手, the back foot following 跟後腳, using the jing to hit 精打, the power of the legs. The is the wood energy, the steps are small, and are able to advance and retreat. Each step is like an encampment「步步為營。」 An jin is the energy of being round outside but square inside, when training the outside looks soft and round and 'moist / slippery', but when issuing power, the internal is square and hard and at right angles. When one strikes the opponent only retreats half a step but has an internal injury. The Classics states, let one "expand and lift their diaphragm, lengthen their muscles/ tendons, the expansion is limitless" 拳經謂：使人「騰其膜，長其筋，勁縱橫聯絡，生長而無窮也。」This is the practice for training the tendons, muscles, and for transforming Qi into Shen. Hua Jin: elastic strength, twisting strength. The mystique of change, the wonder of dissolving. One fist needs to develop a dragon's waist, to twist and turn 龍腰擰扭, to use opposing energy 用阻力 and to hit slowly. The steps are lively, and able to move in a zig zag triangle, and its applications come from the 12 forms. The five fists contain more than six ways of disappating the opponents energy. The form contains six changes and the fists attacks in eight directions. 所謂「式含六變，拳打八方。」 The classics state, "Cleanse and empty the inside, lighten the body, the signs that indicate the interior is clean and empty : the flow of the shen and qi can be used, moving in a circle without hindering the moving and turning of the body, and one is as light as a feather". Hua jin is not divided into bright or dark, hard or soft. Ming jin is Yang, An Jin is Yin, thus Hua Jin is mixing of Yin and Yang with Ying and Yang interpenetrating each other. The Shen and the intention has penetrated the whole body, washing the bone marrow, this is training the Shen to return to emptiness. The three jin, from a theoretical perspective are divided as above. Thus, Ming Jin is jin or power that is easily seen, An jin is hidden and cannot easily be detected. Ha jin is negating the enemy's force and returning it to the enemy. During the training process, each level of training of the five elements has a strict demarcation. Like hand work, foot work, body method, each fist has a unique and fixed training method. It is a complete and complicated process. Ming jin is in the hands, the an jin is in the elbows, hua jin is in the body. Ming jin is hard, an jin is soft, hua jin is elastic. Ming jin trains the Jing, An jin trains the Qi and Hua jin trains the Shen. Ming Jin goes out and returns in a straight line, An jin only begins when stillness reaches its zenith, Hua Jin remains inside and is not revealed. Ming Jin uses power, An Jin uses jin, and Hua Jin uses the intention. Finally they all interpentrate each other, shifting the soft to the hard and shifting the hard to the soft. Hua jin is complete control of Ming jin and An jin, mixed into one body. Actually the three jin are shown within the Xingyiquan system, with form and intention as below: The Five Element Fists contain the Three Jin 五行拳中亦分三勁： Ming Jin : Pi Quan, Zuan Quan 明勁：劈拳、鑽拳。 An Jin: Beng Quan, Pao Quan 暗勁：崩拳、炮拳。 Hua Jin: Heng Quan 化勁：橫拳。 The Twelve Forms are also divided into the Three Jin 十二形中亦分三勁： Ming Jin: Tiger, Horse, Chicken, Eagle 明勁：虎形、馬形，雞形、鷹形， An Jin; Bird, Snake, Bear, Lizard 喑勁：鳥台形、蛇形、熊形、鼍形， Hua Jin: Dragon, Monkey, Swallow, Harrier 化勁：龍形、猴形、燕形、鷂形、 Modern practioners do not explicitly demarcate three levels of training jin, and mainly train Ming jin, as it looks good and is fierce, and stop there. As for An Jin and Hua Jin, many do not understand them and do not practice them. They think that by practicing slowly, and using less force is An jin and do not understand the way to practice Hua Jin at all.http://benotdefeatedbytherain.blogspot.tw/2013/02/a-treatise-on-xinyi-quans-three-jin.html