This allows us to become less tense, to drop our conditioned habits, let go of thoughts, allow qi to flow smoothly, and thus to flow with the Dao. It is thus a kind of moving meditation that allows us to let go of the self (wuwo), and experience no-mind (wuxin) and spontaneity (ziran). A key aspect of Tai Chi philosophy is to work with the flow of yin (softness) and yang (hardness) elements. When two forces push each other with equal force, neither side moves. Motion cannot occur until one side yields. Therefore, a key principle in Tai Chi is to avoid using force directly against force (hardness against hardness). Lao Tzŭ provided the archetype for this in the Tao Te Ching when he wrote, "The soft and the pliable will defeat the hard and strong." Conversely, when in possession of leverage, one may want to use hardness to force the opponent to become soft. Traditionally, Tai Chi uses both soft and hard. Yin is said to be the mother of Yang, using soft power to create hard power. Traditional schools also emphasize that one is expected to show wude ("martial virtue/heroism"), to protect the defenseless, and show mercy to one's opponents. Practice Traditionally, the foundational Tai Chi practice consists of learning and practicing a specific solo forms or routines (taolu). This entails learning a routine sequence of movements that emphasize a straight spine, abdominal breathing and a natural range of motion. Tai chi relies on knowing the appropriate change in response to outside forces, as well as on yielding to and redirecting an attack, rather than meeting it with opposing force. Physical fitness is also seen as an important step towards effective self-defense. There are also numerous other supporting solo practices such as: Sitting meditation: The empty, focus and calm the mind and aid in opening the microcosmic orbit. Standing meditation (zhan zhuang) to raise the yang qi Qigong to mobilize the qi Acupressure massage to develop awareness of qi channels Traditional Chinese medicine is taught to advanced students in some traditional schools. Further training entails learning tuishou (push hands drills), sanshou (striking techniques), free sparring, grappling training, and weapons training. In the "T'ai-chi classics", writings by tai chi masters, it is noted that the physiological and kinesiological aspects of the body's movements are characterized by the circular motion and rotation of the pelvis, based on the metaphors of