 How to discuss the relationship between the realm of experience and emptiness or Buddha-nature was another common theme in Buddhist philosophy. One of the more thorough and influential discussions is the Meditative Approaches to the Huayan Dharmadhātu (Huayan Fajie Guan Men 華嚴法界觀門), attributed to Dushun 杜順 (557–640) (see Fox 2009). According to Dushun, the world of experience can be viewed in four different ways. The first is as phenomena or events (shi 事), which is equivalent to the realm of form. The second is as emptiness, referred to here with the term li 理. The point is that, in one sense reality can be seen as the multitude of phenomena but in another sense it can all be seen as empty, which entails a kind of equality and interchangeability. The third perspective addresses the relationship between emptiness and phenomena, using the relationship between water and waves as a metaphor. The two are mutually encompassing and mutually dependent, just as there is no water without waves and waves are nothing other than water, yet we can focus solely on the wave or solely on the water. The point is that designating a wave is not the same as designating water, yet these designations do not “obstruct” each other. The very same reality can be taken as the phenomena of everyday experience and as emptiness.