First of all, what is a Tai Chi "form"? Basically, a form is a sequence of choreographed moves. The English term is not really a translation of anything in Chinese: the Mandarin term is "taolu", which literally translates as "set road " (set as in a set of moves), ie a sequence of movements that acts as a way to develop skill.
In our school, we keep the beginners' forms short and as accessible as possible to minimise the initial demands and to build confidence. The first, five-movement form can be practised repeatedly in a small, square space and is ideal for a quick run-through in the living room - so there are no excuses for not practising when it is raining! The next sequence adds another five movements, including a couple of more vigorous ones, so that both the Yin and Yang aspects of Chen Tai Chi are included. Finally, the full eighteen-movement short form of Grandmaster Chen Zhenglei, which adds six or seven new techniques, gives the beginner a good introduction to the different ways of moving, stepping and using energy in Chen-style Tai Chi.
But what is the point of learning these sequences of movement? If they are just choreography, wouldn't the student be better off going to a ballroom dancing class?
The East Asian martial arts typically use forms as a central feature of their training methodology, though modern Tai Chi seems to rely on them perhaps more than others; in a typical Karate class, for example, there would be much more emphasis on drilling single moves and various forms of sparring.
Taijiquan - as it is properly termed - began life as a fully functional martial art (the "quan" means "fist"), and it seems to me inconceivable that the original training regimes would not have involved less form training and much more physical conditioning, fighting application practice and sparring up to full contact level. The recent well-publicised defeat of a supposed Tai Chi "master" at the hands of an MMA fighter exposed the delusion that is unfortunately still current amongst some Tai Chi practitioners both in China and in the West that forms practice, qigong and meditation alone will confer self-defence capability.
This does not mean that forms practice was not an important aspect of training, however; it clearly was, though some modern martial artists are skeptical of their value and reject them completely. After all, in the contexts in which the martial arts evolved, which were often violent and in which criminality and banditry were rife, it seems highly unlikely to me that any useless method of training would have been retained; the time spent on forms training - and learning a Tai Chi long form does take a considerable amount of time - had to have been justified. And Tai Chi forms prove to have been remarkably persistent across the various styles and over more than three hundred years of history: the traditional long forms of the Chen, Yang, and Wu styles, for example, basically follow the same sequence and contain recognisably related versions of the same movements. I cannot see that they would have lasted if they had not been of practical use.
It seems to me that there might have been at least three important reasons for forms practice. One is that forms act as a sort of library of techniques of the style; in a culture where illiteracy was high they perhaps functioned as a sort of "memory-bank" to make sure that nothing got forgotten. Secondly, a form teaches combinations of movements; the drilling of single-movements allows a technique to be perfected (up to a point) but the form teaches how they might be linked together. The third reason, however, is, I believe, the most important and that is that the Tai Chi form helps the practitioner to develop the physical characteristics which Tai Chi requires: diligent practice literally starts to reshape the body so that it becomes more functionally effective.
As the focus of Tai Chi training has shifted more towards the health and well-being aspects of the art, this, I think, is the reason why there is now more of an emphasis on forms practice and other training techniques have become less important (in many schools, that is, not all). However, forms practice does mean that Tai Chi works the whole body all of the time: it teaches integrated movement which is directed towards a particular purpose (to push, pull, suddenly emit energy, etc). This makes it more complicated for the beginner, unfortunately; the Tai Chi student needs to develop some independence by actually learning the movement sequences of the form so that she/he can then concentrate more on developing the internal awareness that is necessary for the building of the Tai Chi body.
This, of course, is also what makes Tai Chi so mentally as well as physically stimulating!
Andrew Howard is a Chen-style Tai Chi Instructor teaching in West Dorset, UK.