"Song" (translated as a state of looseness, relaxation, devoid of tension etc.) is one of the most important and fundamental essentials of Taijiquan, and is the ongoing goal of every Taijiquan player.
This is because "song" enables the body to sink; sinking facilitates softness and pliancy; softness and pliancy leads to lightness and agility; lightness and agility results in extreme sensitivity and the neutralising skill that enables entry to the higher levels of Taijiquan.
Within the dynamism of movements, the body must be loose and soft. No part of the body should have a trace of any unnecessary musculoskeletal as well as mental or energetic tension. This is an extremely difficult state to attain.
Even with guidance from a good teacher, the state of "song" can be achieved gradually only after a long period of self discipline and correction, of which there is no end point. It involves a multi-layered understanding of essential principles. It can be said that almost all of the essentials of Taijiquan are directly or indirectly associated with "song". Any action that does not adhere to principle will affect to some extent the quality of "song". For instance, if the frame is not balanced and stable, the muscles and joints contract in order to restore balance during movements, using unnecessary strength as well as creating musculoskeletal tension. The mind become anxious and the attempts become frustrating, affecting mental calmness. Therefore, achieving balance and correct structure is one of the methods for achieving "song".