The interaction of principle and phenomena
Cao-Dong School is characterized by two philosophic doctrines which do not clearly emerge elsewhere in the other chan schools of the late Tang and the Song periods. The first of these, the esoteric teaching of the Five Ranks, was created by Dongshan Liangjie and developed by Caoshan Benji. Its popularity and employment as a teaching device seems to have varied enormously from generation to generation—Dogen Zenji seems to have been little impressed with it—but it is reasonable to say that it has always had at the very least a background presence throughout the later history of Cao-Dong School. Indeed the Song-period chan histories agree in emphasizing Dongshan's Five Ranks as the original teaching of the school, and that alone probably would have precluded the possibility of its complete disappearance in later years.
The second characteristic Cao-Dong teaching, namely the interaction or "mutual interpenetration" of li and shi, principle and phenomena, is of especial relevance to the early Cao-Dong period. It is also included in the Record of Mazu, indicating its probable employment in the 8th-century Hongzhou School, descended from Mazu. It is mentioned explicitly in the Record of Dongshan, and can be seen as the basis or underlying strategy for the formulation of the Five Ranks, a systematization of how principle and phenomena integrate and act upon each other. Shitou Xiqian, in the fourth generation before Dongshan, emphasized the teaching of li and shi, and this more than any other single factor has led to the sense of a Cao-Dong pre-history that antedates the actual founding of the sect in the 9th century; that its real roots extend back to the middle of the century preceding; and that Shitou Xiqian must qualify not only as a "Cao-Dong ancestor," but perhaps to some degree as one of the school's unrecognized founders.
Another circumstance that heightens this attitude is the adoption for daily chanting of the two major doctrinal poems of both masters, namely The Agreement of Difference and Unity by Shitou and The Song of the Jewel Mirror Samadhi by Dongshan, thus conferring a kind of liturgical canonization in the temple ceremonies. Both poems have much in common, and in the Cao-Dong context they complement each other remarkably. They have also been highly regarded by the other chan schools, and they are generally regarded as masterworks of Chinese Buddhist literature in general.
The teaching of the interaction of principle and phenomena comes to Cao-Dong from the Huayan School, one of the most remarkably innovative schools of Chinese Buddhism, which emerged in the 7th century, during the lifetime of Huineng. The school receives its name from Huayan jing, the Avatamsaka sutra, or Flower Ornament Sutra. Among Mahayana sutras, the Avatamsaka is absolutely unique. It is an enormous work, actually a collection of separate writings which were combined in the late 3rd or early 4th centuries CE, very likely in the forgotten desert kingdoms located in the far southwest of today's China. It presents a panoramic vision of Mahayana Buddhist cosmology, which places Buddha at the center of a universe filled with numberless worlds and world-systems, surrounded by an assembly of buddhas and bodhisattvas who are gifted with all varieties of extraordinary telepathic powers, lost in rapture and fully absorbed in the all-pervading, blazing radiance of the Buddha's samadhi. In addition to this Buddhistic vision of paradise, the final section of the sutra tells the story of the youth Sudhana, who embarks upon a long pilgrimage to receive teachings from fifty different advisors, and thus serves as a model for all seekers following the bodhisattva path.
The Avatamsaka Sutra is not only the most grandiose visionary work in the history of Mahayana Buddhism, but certainly one of the most imaginative and inspired masterworks of religious literature anywhere. Philosophically, it unites the Mahayana teachings of emptiness and thusness and Buddha-nature, and in so doing it indicates the future of chan. It also identifies the human mind with the physical universe, which is also seen as identical with Buddha. In fact, the Buddha, the mind, sentient beings, and phenomena are one and the same. Seen from the ultimate truth of non-duality, the traditional view of dependent arising receives a suddenly positive meaning, since ignorance is also enlightenment.
The sutra is also full of symbolism expressing universal interdependence, interaction, identity of opposites, and unity within difference, themes which coincided to a considerable extent with pre-Buddhist native philosophic ideas in China. Translated into Chinese by Buddhabhadra around 420 CE, the Avatamsaka Sutra instantly magnetized the interest of Buddhist practitioners and scholars alike, just as it continues to fascinate to this day. In the mid-600's, its study gave birth to the Huayan School, whose founders attempted to explain systematically a series of philosophic ideas which they perceived in the sutra. These ideas aroused widespread and immediate interest in all the contemporary Chinese Buddhist schools, especially in the emerging chan schools. That the chan and Huayan directions seemed more than compatible is demonstrated by the career of the Fifth Patriarch Kueifeng Zongmi (780-841), who was also recognized as a master in the chan school founded by Shenhui and known as Hoze School [Japanese: Kataku]. Zongmi is an important figure of his times for several reasons, and quite obviously he must have considered chan practice as an appropriate consequence of Huayan ideas, derived in turn from the Avatamsaka.
The teaching of the identity and the mutual penetration of principle and phenomena, central to the establishment of Cao-Dong School, was evidently first formulated by Tuxun (557-640), who came to be regarded as the original founder of Huayan School. The early Huayan treatise ascribed without certainty to Tuxun and entitled Fajie kuan men (Reflections on the Dharma Realm) explains the relation between li (principle) and shi (phenomena), and the various modes of interpenetration of both. Because principle, meaning the general truths or principles which govern phenomenal reality, interacts worth phenomena "without mutual obstruction (wu ai), both principle and phenomena are able to enter into or penetrate each other; to include, incorporate and fuse with each other, without either losing its respective identity.
This conception receives further elaboration in the writings of Fazang (643-712), who mentions the teaching in the introduction to his commentary on Awakening of Faith in the Mahayana. Fazang was known later as Huayan sect's third patriarch, after he had developed the "golden lion" comparison, which became instantly popular. The statue of the lion represents its phenomenal existence, but the gold of which it is made is its principle, which is itself formless, but for that reason can adopt any form which is required. Because every part of the lion is made of gold, principle is necessarily present in each of the parts: the whole is identical with its parts, and vice versa. Consequently all phenomena manifest one principle, and this one principle achieves its expression in the world of phenomena.
If in Buddhist terms we equate principle with emptiness, which of course is the one quality that characterizes all phenomena, then emptiness is therefore form, and form is emptiness. Emptiness is for this reason "the spiritual source" (Shitou Xiqian) of phenomenal existence. This spiritual source is also identified, in the Huayan tradition, not only with dharmadhatu, the true "dharma realm" invisibly permeating all things, but also with tathagata-garbha. Phenomenal existence is now seen as the one mind and body of the Buddha. Just as the theories of emptiness, thusness and Buddha-nature are unified in Huayan thinking, they are continually integrated in the language of sign and symbol employed by the great chan masters.