Even just among Yang Style Tai Chi, there are many styles and forms. The most popular is the one developed by master Yang Chengfu, the so called Large Frame 108 form. The are forms from the earlier generations, the Yang Banhou / Yang Shaohou Fast Form and Small Frame, the Yang Jianhou Middle Frame. Then we have the Cheng Manching 37 Form, the Yeung Saucheung (Yang Chengufu’s son) forms, Dong/Tong lineage forms, the Guang Ping form, the secret Imperial forms, and now of course myriads of Wushu-infused athletic forms. Plus many others.
In the end though, as long as the form follows and that the practitioner adheres to the Tai Chi Principles (which are laid out fairly clearly in the Tai Chi Classics), they are all good.
The original Tai Chi or what became Tai Chi, probably derived from just a few postures similar to Xingyi. Indeed, Founder Wang Xinagzhai said the original Tai Chi was just “Three Old Cut” – although that reference was never verified by others.
Regardless, the Principles were distilled after the elders discovered the marvelous outcome of certain (internal) practices. It truly is the gem of the Tai Chi practice. The forms are just vehicles.
Note that even for master Yang Chengfu, his form when he was young is quite different from when he was older.
