太極拳經 張三丰 Principles of TaiChi Chuan by Zhang San-Feng

太極拳經 張三丰

一舉動周身俱要輕靈，尤須貫串。氣宜鼓盪，神宜內斂，無使有缺陷處，無使有凹凸處，無使有斷續處。其根在腳，發於腿，主宰於腰，行於手指，由腳而腿而腰，總須完整一氣，向前退後，乃能得機得勢。有不得機得勢處，身便散亂，其病必於腰腿求之，上下前後左右皆然。凡此皆是意，不在外面，有上即有下，有前則有後，有左則有右。如意要向上，即寓下意，若將物掀起而加以挫之之力。斯其根自斷，乃攘之速而無疑。虛實宜分清楚，一處有一處虛實，處處總此一虛實，周身節節貫串，無令絲毫間斷耳。

長拳者，如長江大海，滔滔不絕也。掤、履、擠、按、採、挒、肘、靠，此八卦也。進步、退步、左顧、右盼、中定，此五行也。掤、履、擠、按，即乾、坤、坎、離、四正方也。採、挒、肘、靠，即巽、震、兌、艮、四斜角也。進退盼顧定，即金木水火土也，合之則為十三勢也。

Principles of TaiChi Chuan by Zhang San-Feng

With every movement string all the parts together, keeping the entire body light and nimble.

Calmly stimulate the Qi, with the Spirit of Vitality concentrated internally.

Avoid deficiency and excess; avoid projections and hollows; avoid severance and splice.

The energy is rooted in the feet, issued through the legs, directed by the waist, and appears in the hands and fingers.

The feet, legs, and waist must act as one unit, so that whether advancing or withdrawing you will be able to obtain a superior position and create a good opportunity.

Failure to obtain a superior position and create a good opportunity results from the body being in a state of disorder and confusion.

To correct this disorder, adjust the waist and legs. All directions — upward and downward, forward and backward, leftward and rightward — need the same requirements.

All of these are to be directed by the Mind-Intent and are not to be expressed externally.

If there is above, there must be below. If there is advancing, there must be withdrawing. If there is left, there must be right. If the initial intent is upward, you must have downward intent.

If you want to lift something upward, you must have the intent of pushing downward. Therefore, its root will be severed, and it will be toppled immediately and certainly.

Clearly discriminate the substantial and insubstantial. There is an aspect of substantial and insubstantial in every part of the body.

When the entire body is integrated with all parts, connected together, it becomes a vast connection of positive and negative energy units. Each positive and negative unit of energy should be connected to every other unit and permit no interruption among them.  

Long Boxing (TaiChi Chuan) likes a long river flowing into the wide ocean ceaselessly.

Peng, Lu, Ji, An, Cai, Lie, Zhou, and Kao are related to the eight trigrams. Forward step, Backward step, Look left, Gaze right, and Central equilibrium are five elements.

Peng, Lu, Ji, An, correspond to ☵, ☲, ☳, and ☱ in the four principle compass directions. Cai, Lie, Zhou, and Kao correspond to ☰, ☷, ☶, and ☴ in the four corner directions.

Forward step, Backward step, Look left, Gaze right, and Central equilibrium are related to metal, wood, water, fire, and earth – the five elements.

These combination [8+5] are called the Thirteen Dynamics.

Reference:
http://www.egreenway.com/taichichuan/chang1.htm#Principles
https://brennantranslation.wordpress.com/2013/05/25/the-taiji-classics/