This the third of the Taijiquan Classics is a series of short statements that focus on martial arts self-cultivation through the development and coordination of the energetic functions of mind, qi, and body. The following entry including its annotations has been taken or adapted from various translations and commentaries. These sources are cited in the text, and in the list of Sources below. When no single source is given, the information was derived from more than one place and is listed as an editor's comment. 
Yang style illustrations based on Master Yang Chengfu's postures
1. Use the mind (xin) to calmly and deeply sink vital energy (qi), then gather and guide it into the bones ["harden the bones"].
"After long periods of practice of internal energy awareness, you will be able to command your mind to guide your internal energy to any part of your body at will …. In advanced stages one can condense the internal energy into the bone marrow throughout the body and generate the ch'i into the high-frequency vibrations known as the internal power, jing or (jin). [Liao 109-110].
2. Smoothly and completely circulate the Qi in the body. Then physical movements will easily obey the mind (xin).
When chi [qi] becomes the inner energy it is similar to the gas or steam that propels a modern piece of machinery…[which then] will perform its functions according to the direction of the operator. [Da Liu 109].
3. If the spirit of vitality (jing-shen) is raised, there will be no slowness or feeling weighted down. This is accomplished with the top of the head pulled up as if suspended from the heavens.
When practicing T'ai Chi you must first raise your spirit of vitality (the essence of the whole body). To do this, your head must be upright and feel as if it were suspended in the air so that an active and alert energy will arise from the upper dantian, (between the two eyebrows), to the pai hui [bai hui, GV20] acupuncture point (at the crown of the head). [from Liang 23].
4. Mental intention (yi) and Qi need to dynamically interact . Then there will be the marvelous pleasure of smoother and more dynamic movements. This is called the transformations and turnings of the empty and the full.
In taijiquan, intention and inner life energy (Qi) should continuously turn about and transform each other. Mind, energy, and movement can each function as Yin or Yang as each interacts with the other—and the opponent—changing from inputting or outputting. [Liao 112].
5. When issuing forth internal force (jin) be calm, relaxed and grounded, with your aim focused on one point.
"The transfer of power must be completely projected, concentrated in one direction only, in order to allow the vibration of your power to accelerate and exceed the speed of light." [Liao 113].
6. Stand comfortably straight and relaxed, ready to respond to an attack from any of the eight directions.
The eight directions here refer to the four sides and four corners surrounding the practitioner. [editor's comment].
7. Circulate and conduct the Qi as if you were threading a pearl with nine crooked pathways.
The pearl with its crooked passageways is a metaphor for the body and its many energy pathways (e.g. meridians, vessels, channels). [Davis 128].
8. Move power (jin) as if it were steel tempered one hundred times; no opposition can resist being destroyed.
9. Appear as a falcon seizing a rabbit; have the spirit (shen) of a cat catching a mouse.
"In performing the forms, you should be like the eagle which glides serenely on the wind, but which can swoop instantly to pluck a rabbit from the ground…. Your mind should be centered, like the placid cat, peaceful but able to respond instantly to the scurrying mouse." [Liao 115].
10. Be still as a lofty mountain; move like a great river.
11. Store energy as if drawing a bow. Release energy (fa-jin) as if shooting an arrow.
12. In what is curved seek the straight. Store and then release.
Within the spiraling movements of taijiquan, and inside the curved arms, legs and even fingers making those movements, the energy always moves inside in a straight line. [Da Liu 112].
13. Power (Li) comes from the spine. Steps vary according to the movements of the body.
Note: some translations have "jin" rather than "Li" and "back" rather than "spine." [editor's comments].
"Changing just your stance or your steps without moving your body will result in loss of control, improper posture, and loss of balance." [Liao 117]. In other words the entire body should move as a single unit. [editor's comment].
14-a. To receive is to promptly release.
When your opponent strikes the left side of your body, you neutralize [receive] his striking energy by withdrawing and turning your body to the left and at the same time you strike him with your right hand. [Liang 26]. "Release" is like "setting off fireworks." [Yabla.com].
14-b. Broken off, but reconnects.
"The word "fu" translated as "reconnects" also means "recovers," "returns," "resumes." [Yabla.com].
If the inner energetic [jin] connection from you to your opponent is temporarily broken, as long as your mental connection to him is still firm, it [the Jin] will immediately recover and connect. Then it can be externally issued as (in 14-a) an explosive "release." [editor's comment].
15. In going forward or back there must be folding [of the joints of the arms and legs]. In advancing or retreating there must be variation [in foot movements and body turning].
When you move in and out, your entire body acts like an accordion, folding and unfolding. When you move forward and backward, your stance changes in a varied, dynamic manner. [Liao 117].
16. Extremely soft, after that extremely hard (and strong).
[Editor's comment: Having the body relaxed and pliable enlarges its ability to increase its qi and jin.] "If air [which is very soft] is compressed into a tire, the tire becomes hard as a rock and can bear many tons for a long distance." [Da Lui 113].
17. Exhale and inhale correctly; then (there is the possibility of being) flexible, nimble and agile. The Qi should be cultivated in a natural and straightforward manner, then no harm.
Proper breathing—never forced or exaggerated—is best learned from a master teacher. This enables the gathering, development and storage of Qi, which is basic for both qigong and taijiquan. [editor's comment].
18. Strength (jin) by this [i.e., breath work] is stored in the bent [i.e., "curved" joints, body, movements] and becomes abundant.
19. The mind (xin) is the commander; the Qi is the flag; the waist (yao) is the banner.
The Mind, as Commander-Chief, directs the Qi, which is likened to the small flags that soldiers use in combat. The "banner" represents the large flag of the generals located at the center of the army, here being the waist (lower torso). The waist carries out the directions ("orders") of the mind. [editor's comment].
20. In practice, initially make big stretching movements and gradually reduce them to small compact movements. In this way eventually they will become perfectly fine and delicate. [Cheng & Smith 111].
The larger and more extended form will serve better for instruction and correction purposes. After gaining command of the art, you can then discover the same principles in a circular and concentrated form. If instead you begin with compact, concentrated movements, it might not be possible to later perform a large and extended movement correctly. [Liao 120].
21. (It has been said) – If the opponent is motionless then you are motionless. At the opponent's tiniest movement you move first.
You sense his intention and move before his Jin is emitted. [Dr. Yang 9].
22. Inner power (jin) seems relaxed, but it is not. Ready to be expressed, but not yet. If it breaks (snaps) off, the intention (yi) remains uninterrupted.
The energy outwardly appears relaxed but it is inwardly concentrated, ready to discharge at any moment. If the energy is broken off, the attention of your mind still remains. [Cheng & Smith 111]. See 14.b above.
23. (It has been said) – First in the mind then in the body. With the abdomen relaxed, the Qi permeates the bones. The mind (shen) is at ease; the body is calm. Carve and engrave these teachings into the center of your mind and heart [xin] so you always remember them.
24. Be sure to remember as soon as one part moves, every part moves. One part still, every part still. [Brennan].
The body always moves as a unit. Don't push with just a hand or arm, push with your entire body, mind, and Spirit. When you are still, be entirely still, with no stray motions. [Dr. Yang 10].
25. When moving back and forth, the vital energy (Qi) sticks to the back, and enters and is gathered into the bones of the spine.
When the ch'i [qi] adheres to the back of your body during the time of pulling and pushing, it will eventually permeate the bones, causing a natural intrinsic energy to be developed, which is tremendously powerful when released. [Liang 31].
26. Within, strengthen the spirit of vigor (jing-shen); on the outside appear calm and at ease.
27. Step like a cat. Use energy (jin) as if spinning silk.
Move with light and agile steps. Move inner-energy as if drawing silk from a cocoon, smoothly and without stopping or it will break. [editor's comment].
28. Keep the mind (yi) focused on the spirit of vitality (jing-shen), and not on the Qi. If you concentrate on the Qi, its circulation will become sluggish and you will become powerless and lack strength. A person not thinking about Qi obtains genuine hard strength.
When first learning about taijiquan, you need to mentally concentrate on sensing and moving the Qi. But when that goal is reached you should forget about the Qi (energy and breathing) and just go about using it—as in "don't think, just do." In western terms this could be called "Flow," or "In the Zone." [editor's comment].
29. The Qi is like a wheel; the waist (yao) is like an axle.
The circulation of Qi should be well balanced and constantly moving, as if turning a wheel. The waist (yao) and the mind move and direct this Qi, which interacts with Li (physical muscular strength) to create explosive fighting movements (fa-jin). [editor's comment].
Chinese Words Defined in the Context of Taijiquan:
Jin (or jing, or chin), 劲."Energetic power" or "inner-strength." A combination of "Li" (muscular power) and "Qi." [Dr. Yang 110].
Fa-jin, or 發勁/发劲. Externally and explosively issue or discharge Jin power. This has been likened to the energy that issues from the tip of a bull whip. Following a spiral movement of delivery, the energy is concentrated along an ever-narrowing ribbon of leather until it is expressed with great force and flawless precision at the delicate tip.
Jing-shen, 精神. Literally "spirit mind" or consciousness. But in taijiquan it more often means a "spirit of vigor, vitality and drive."
Li, 力 (sounds like "lee"). "Physical muscular strength."
Qi (or chi), 氣 (sounds like "chee"). The vital energy, or breath, that grants us life.
Shen, 神. Literally "Spirit," but as in English this term is open-ended with various seemingly contradictory definitions. I prefer "Mental Energy Consciousness." Others have: the source of instincts and behavior; spirit; soul, mind; god, deity; supernatural being." But in the vocabulary of taijiquan the best definition may be, "spiritual energy."
Xin - 心 (sounds like "shin"). Heart and mind: the merging of emotion, desire, goals, wishes, attitude and aspirations.
Yao - 腰. simply translated as "waist" but can also refer to the lower torso, or the pelvic region including hips, loins, and lower spine. Also the body's center of gravity, and the dantian.
Yi - 意 - (sounds like "ee"). Mental intention; a state of silent mindfulness of the will.
^ The title in Chinese is 十三勢行功心解 and is often translated as "The Mental Elucidation of the Thirteen Postures." "Thirteen Postures" is an early name of what is now called "taijiquan," or more commonly "tai chi." The word "posture" implies movement as in one gesture or position seemlessly flowing into another one. Author Wu Yuxiang's name in Chinese is 武禹襄.
^ The "editor" refers to John Voigt, editor of Qi Encyclopedia.
^The upper dantian is a place of energy storage and cultivation. In other traditions it might be called "the third eye." In taijiquan it is often placed between the eyebrows, but it is also considered to be several inches behind that spot in approximately the center of the head in the area of pineal gland.
Paul Brennan, translator. “Understanding How to Practice the Thirteen Dynamics”
[Expositions of Insights into the Practice of the Thirteen Postures] in An Outline of Taiji Theory. [includes the Chinese text].
Dr. Yang, Jwing-Ming. “Thirteen Postures: Training Comprehension of the Thirteen Postures” [pp. 1-12] in Tai Chi Secrets of the Wu & Li Styles. [The “Wu” in the title refers to Wu Style originated by Wu Yuxiang. The “Li” refers to his nephew, Li I-yu.] YMAA, 2001.