Four Square Forces can be applied in a circular manner. There is no difference between a "Square" force and a "Circular" force.
The Four Square Forces are the four main forces in the Taiji martial art system.
Some contemporary writers consider that the Four Square Forces can only be used in 4 straight forward directions. According to these writers, the Four Corner Forces were introduced to make up the balance such that a practitioner can deal with his opponents from all directions. Some even said that the Four Corner Forces are high level forces which are more powerful than the Four Square Forces and that they are embodied in and practised through the "Circular Forms". These views are however, a departure from the Taiji martial art principles.
Four Square Forces can be applied in a circular manner. There is no difference between a "Square" force and a "Circular" force, if you know how to do it. Likewise, there is no such distinction between a "Square Form" and a "Circular Form" if you know the essence of the art. Hence, there is no need to introduce to the system "new " measures to "make up the balance".
What then are the Four Corner Forces?
According to "On the Art of Taiji", the Four Square Forces provides a Taiji practitioner the ammunition required in action. However, a practitioner, unless extremely skillful, will inevitably alter his best positioning in action. What can he do then? The answer is in the Four Corner Forces.
The Four Corner Forces are remedial tools available to a Taiji practitioner when he loses his optimum position. Hence, they are supplemental to the Four Square Forces and the practitioner should recover back to the Four Squares after regaining the optimum position. When a practitioner uses the Four Corner Forces, he is in a recovery mode.
[typo (underlined) fixed on 1 May 2014]
