These books were purchased by me in the past 30 years or so. The best book appears to be "On the Art of Taiji", a Qing classic, a photo copy of which was reproduced in a book published in early 80's. "On the Art of Taiji" discusses in depth on the importance of getting back to the "original body condition" through martial art trainings. It also talks about the stage of "Know your own self" and the stage of "Know others".
This book was written in old traditional Chinese language and is very difficult to understand - even for a native speaker. I have tried to explain the contents of it in simple English Language - see some of my previous articles.
It is not an instructional manual. You need to learn the basic trainings and application skills from a master who knows the art.
Another book I like most is "A Collection of Taiji Classics" published in the mainland in early 90s. It includes the texts of most well known Taiji classics (including extracts of "On the Art of Taiji"). It is a documentary textbook and does not include commentaries by contemporary writers (that's why it is good).
The classics provides:
1. The definitive principles on the art - what the art is about, what to learn and what the goal is.
2. Guidelines for the students to follow so that they will not depart from the basic principles in their trainings.
No matter how good a book is, it cannot replace a master - the classics do not teach you "how" to do it. A good master should be able to demonstrate to his students in action the taiji principles (as set out in the Taiji classics and not some contemporary "invention") and provide the right training methods to the students so that they can do the same thing within a reasonable period of time. A student can also know if he has been following the right master, using the classics as the yardstick against what has been taught.
I also have a lot of books published by contemporary Taiji practitioners. I regret to say that many, if not all, of these books are not helpful. It may be that some of these writers are skillful (giving them the benefit of doubt), they did not disclose any valuable information to the readers in these books. Many of these books usually include a set of photos (covering more than 2/3 of the book) with the writers practising the form, plus a reproduction of a few pieces of Taiji classics (covering 10 more pages), with some simple (or intentionally complicated) explanations. It is unlikely that a learner could improve his skill by reading these books.
I wish I could find out some positive methods to get rid of these contemporary writers' books on my bookshelf. I of course wish to have all my money back - together with interest!