Tai chi (taiji) is the universal principle behind birth and transformation. Though tai chi has no form, shape, sound nor colour; all forms, shapes sounds and colours are born and transformed through it. : And so tai chi simply refers to stillness and movement, while yin and yang refer to tai chi. ... In tai chi chuan, because the principles are based on the transformation of tai chi (taiji) - movement and stillness, yin and yang as well as opening and closing - one seeks stillness in movement and movement in stillness. Movement is primarily a study of empty and full, which refer back to yin and yang. Students should first know about the principles of stillness and movement in yin and yang before proceeding with their studies.