To be precise, Tai Chi is categorized as an internal soft-style kung-fu. "Internal" means that the emphasis is on strengthening the internal body, the muscles, tendons, bones, internal organs, and it follows a quiet, meditative training that lets the body do the job without forcing it. While external training, such as in gym exercises and weight lifting, works on certain groups of muscles separately, internal training works on the whole body and the mind as one. The mind needs to be empty, clear and calm. Internal systems take longer to achieve, but it is very powerful and deceptively so, with no obvious or flashy moves like high jumps and kicks. Internal systems offer a more practical and economical approach to fighting. At the same time, Tai Chi has a greater healing effect on the body as opposed to other systems.
The characteristics of Tai Chi are deep breathing, circular movements, smoothness, and the capacity to be slow-yet-fast, with the nervous system completely attentive. The practitioner of Tai Chi doesn't try to use force against force, as in other styles. Hsing-Yi, for example, is a popular internal style of kung-fu that is harder rather than soft. "Will Boxing", and is characterised by aggressive, seemingly linear movements and explosive power A Tai Chi practitioner learns to yield to an opponent's force while keeping in contact with his body and seeking an opportunity to strike, instead of matching force against force. This best illustrates the Tai Chi principle of four ounces deflecting a 1,000 pounds, and is the essence of Tai Chi's power.