 Throughout heaven and earth is the mind-heart (xin), whose changes are unpredictable. It is inexorably manifested in myriad different forms. The mind-heart has no fundamental substance. Fundamental substance is that which is achieved by its efficacious effort. Therefore, to plumb the principle (li) is to probe the myriad different forms of this mind-heart, not the myriad different forms of the myriad things. (Huang MRXA: preface 9) 