The central problem addressed in this paper is the explanation of the dharma-dhātu (法界) as it is presented by Cheng-guan (澄観, 738-839), the fourth patriarch of the Hua-yan (華厳) school of Chinese Buddhism. The Chinese equivalent of the Sanskrit word dharma-dhātu developed into a central idea expressing the ultimate truth and the world view of the Hua-yan sūtra as presented by Zhi-yan (智儼, 602-668) of the Hua-yan school. After passing through the systemization of Hua-yan doctrine by Zhi-yan and Fa-zang (法蔵, 643-712), this Hua-yan view of the dharma-dhātu was completed by Cheng-guan, and it is called the four kinds of dharma-dhātu. The present paper focusses on the following points: How did Cheng-guan understand the dharmadhātu and how did he explain it? By considering all his commentaries related to Hua-yan thought, I will show that his predominant interest was focussed on the problem of the dharma-dhātu, and I will try to show that the explanation given by Cheng guan is divided into three parts: 1) The dharma-dhātu as characterized by non-obstruction of noumenon and phenomena (理事無碍). This is the basis of Cheng-guan's understanding of the dharma-dhātu, and he comprehends these two as inexhaustible and non-obstructed. He develops the concept further, culminating the "Four dharma-dhātus theory". Here he was influenced by the text "On the meditation of Hua-yan dharmadhātu (法界観門)" ascribed to Du-shun (杜順). 2) The dharma-dhātu of cause and effect (因果) and dependent origination (縁起). When discussing the principal chararcteristics of the Hua-yan sūtra, he explains cause and effect and dependent origination as being placed on one line. He does this because he analyzes the sūtra as consisting of sequences of cause and effect. Consequently, if one considers the relationship of this idea to Bodhisattva practices (菩薩行), then the Hua -yan sūtra itself takes the position of practice, and the sequence of practice expressed as the circularity of the five steps of cause and effect (五周因果) becomes a concept of great importance. 3) The dharma-dhātu as the origin (根源性) and the ultimate (究極性). This is an interpretation starting from the point of view of nature-origination (性気), meaning that the dharma-dhātu is not only the truth one has to attain finally, but is at the same time the origin that brings forth all things. Cheng guan says about the dharma-dhātu that from the ultimate viewpoint it is not only the basis of the Hua-yan sūtra but of all other sūtras and dharmas as well, and it is from a fimdamental viewpoint the basis of the delusion (迷) and enlightenment (悟) of beings, from which the Buddha as well as Bodhisattvas appear. Because it is further regarded as not being separate from the Pure One Mind, it is defined as the basis of Bodhisattva practices. The way Cheng-guan understood the concept of "the dharma-dhātu viz. the one mind" is basically founded on the traditional "Awakening of faith" - like understanding predominant in the Hua-yan school, but one can detect some influence of the meditation of ?ūnyatā (空観) as well. Further, the understanding of the "Ten mysterious gates (十玄門) " as being the concrete content of the dharma-dhātu is considered to be based on the concept of "cittamātra (唯心, consciousness-only)", and this had a big influence in giving direction to the further development of Hua-yan doctrine after Yan shou (永明延寿, 904-75) later in the Song period (宗代). As mentioned above, we can interpret Cheng-guan's understanding of the dharma-dhātu as having three forms and categories. In addition, by means of interpretation one would recognize more clearly and deeply that the dharma-dhātu is an important feature of Hua-yan thought.
