From the time of Chen Wangting (1580-1660), the history of tai chi is fairly well known and documented. However, it is widely believed that tai chi has roots going back at least a couple of hundred years more.
Zhang Sanfeng (张三丰), a Taoist monk, is a legendary figure said to have been inspired when he witnessed a snake fighting a crane in the Wudang mountains (left, Wudang mountains in spring 2017, my photo). Zhang allegedly wrote the Taijiquan Jing. Jīng (经) means classic text or canon. The Jing is the earliest of the documents called the Tai Chi Classics. Here are a couple good online translations:
The Jing includes the basic tenet that Jìn (劲) is rooted in the feet, generated though the legs, directed by the waist, and expressed through the fingers. Jin, in the context of tai chi, means force or energetic power.
The eight energies are enumerated in the Jing—掤 péng, 捋 lǚ, 挤 jǐ, 按 àn, 采 cǎi, 挒liè, 肘 zhǒu, and靠 kào—as well as the five directions: 进步 jìnbù (advance), 退步 tuìbù (retreat), 左顾 zuǒ gù (attend to the left), 右盼 yòu pàn (anticipate right), 中定 zhòng dìng (hold the center). Together these are identified as the thirteen essential postures of tai chi.
Below, Taoist temple from the summit of Wudangshan (my photo, 2017):
That the body should move as a unit, that the form should be continuous and unbroken: these familiar and central principles of taijiquan are contained in the Jing attributed to Zhang Sanfeng. Here is a good biography (so to speak) of Zhang: http://qi-encyclopedia.com/?article=Zhang-Sanfeng
Another legendary figure in the obscure origins of Tai Chi is Wang Zongyue (王宗岳), who may or may not have been a student of Zhang Sanfeng. Wang is generally credited with authoring a second classic text, Taijiquan Lun, the Tai Chi Treatise. Lùn (论) means theory or treatise.
Here are a couple of good online translations. The first offers an interesting note about the authorship of the treatise.
The entire section on the martial arts in the Qi Encyclopedia (http://qi-encyclopedia.com/?portal=Martial%20Arts) is an excellent source of translations and articles about the classic texts of Tai Chi. So is Lee Scheele’s online tai chi notebook: (http://www.scheele.org/lee/taichi.html).
The Taijiquan Lun contains the idea that taiji begins with wújí (无极), which translates as eternity or infinity but in practice, it seems to mean stillness, neutrality, or more specifically the neutral, quiet, meditative stance from which every moving form begins.
From wuji, when the movement begins, yin and yang, the opposites, become distinguishable. Left and right. Fast and slow. Upward and downward, hard and soft, and so on. Every movement within the form is definable in terms of yin and yang, opposites. When movement stops (at the end of the form), yin and yang once more come together into the quiet meditative state.
Some additional vocabulary for these basic concepts: dòngjìng (动静) is movement (dong) and stillness (jing). The characters in the treatise are traditional. The simplified characters for yin and yang are阴阳 (yīnyáng). Yin and yang separate (分 fēn) and come together (合 hé).
There should be neither lack nor excess: I interpret this to mean that there must be a balance of yin and yang in every movement—this is something that one of my teachers, Grandmaster Aiping Cheng, has just recently been telling me. The challenge is to identify the yin and the yang in a movement, and then to understand how to balance them.
Two more important concepts from the Lun: 走 zǒu and粘 zhān or nián. Romanizations vary for these words. What I have just given is the standard Pinyin and simplified characters. Zou is sometimes written Tsou, zhan as chan. Zhan and nian mean the same thing: sticky.
Zou (or tsou) is the word for yielding to force. Zhan or nian is the word for sticking, the technique of following your opponent, maintaining contact, and matching his speed (fast or slow) and position (high or low).
Wherever the opponent attacks, he should find emptiness; when he withdraws he can’t get away. These fighting skills are not easily mastered, but they are critical: without technique, fighting can never be anything but the strong overcoming the weak with brute force.