I thought I would add a little to Louis' interesting contribution.
Barbara Davis' The Taijiquan Classics
also has a little material on Qi Jiguang. Since I have no personal connection to her or her book, I would say that it is a must-buy. I am ashamed to say that I have not finished reading it yet, but what I have read so far is quite interesting. Louis has posted some comments about it before.
Davis discusses some of the origin theories and the difficulties peculiar to Chinese historical materials in evaluating them. She has some interesting things to say specifically about Qi Jiguang. Here is a quote form her chapter "A Brief History of Taijiquan":
"The Ming Dynasty (1368-1644) saw publication of A New Treatise on Disciplined Service
(jixiao xinshu) by General Qi Jiquang (1528-1587). Qi's book included a chapter called the "Boxing Classic" (Quanjing) [Davis has a footnote here saying that this chapter is reproduced in Wile's T'ai Chi's Ancestors
, pp. 7-35.] In that chapter, Qi listed more than a dozen boxing styles. He selected thirty-two moves from them and constructed an amalgamated routine. The chapter includes pictures of the moves and mnemonic ghymes about their applications (see Figure 2). Qi noted that boxing was not of use against superior arms, but was still useful for its discipline. The book also included an excerpt of Yu Dayou's (1503-1580) treatise on weapons called the "Sword Classic" (Jianjing), which exhibited concepts such as softness, listening, and sticking that we now associate with taijiquan." (pp. 4-5)
A few pages later, Davis has:
"Many of the Chen-style moves are similar in name and appearance to martial arts moves depicted Qi Jiguang's book, A New Treatise on Disciplined Service
, mentioned above. In view of the overlap betweeen Chen-style moves and Qi's moves, some have speculated that Chen Wangting studied Qi's manual and derived his system of boxing from it. (Footnote 10: To make a stronger link between Chen-style taijiquan and Qi's material would necessitate, among other things, a thorough survey and analysis of boxing names and moves used in these early periods, since names of moves and the moves themselves vary even within present-day taijiquan sytles. Other Chen family written material would also have to be analyzed in more detail. See the start of this process in Hu, 'Ch'en Chung-sheng' and 'Ch'en-shih chia-p'u.')" (p.
I find out all this quite fascinating, however quite complex to evaluate. For example, even a "proven" link between Chen-style Taijiquan and Qi's material does not necessitate that Chen Wangting consulted Qi's manual. Chen and Qi could both have drawn on knowledge of other sources with a common origin.
Another example is understanding how much external commonalities, like similar postures, truly reflect internal commonalities. In other words, how much does an analysis of Chen's raw material ultimately tell us about what he created for Chen Style as a whole?
Lastly, we have the issue of the continuous cross-current of martial ideas and styles, like Qi's use of Yu Dayou's Sword Classic
. Does emphasizing one thread of Taijiquan's development give insufficient weight to the sharing between martial arts and the artists skilled in those arts? In other words, how much of anything is truly developed from scratch or maintained in pristine form without external influence?