T'ai Chi is a Martial Art

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T'ai Chi is truly benevolent and peaceful, yet it is also concentrated and determined, and no less a fighting art than Kung Fu, Karate or Tae Kwon Do.  Each movement can, and does, have any number of self defense applications.  No, of course, you don't move slowly, if you're called upon to defend yourself.  But, just as Bruce Lee emphasized in Jeet Kune Do, you move with economy of effort and abide by principles of calm and centering.  If you need to move quickly, therefore, move quickly.  If not, then don't.