大乘義章 8.72

8.72

第一釋名。眼等六根、色等六塵及與六識，是其十八。能生曰根，能生識故。能坌名塵，坌污心故。然此色等，當法立名，名六境界。而言塵者，偏對染心以彰名也。良以淨心多緣理生、染依事起，故偏對染以名塵矣。能了曰識，了諸塵故。此之十八，經名為界，亦名為性。界別名界，性別名性，諸法性別故名為界（此一門竟）。

First, explaining the names: the six faculties such as the eye, the six objects such as form, and the six consciousnesses constitute the eighteen. That which can generate is called a faculty (indriya), because it can generate consciousness. That which can defile is called an object/dust (guṇa/viṣaya), because it defiles the mind. However, these forms and so forth, established in name corresponding to the dharmas, are called the six sensory domains. The term 'dust' specifically reveals its name in contrast to the defiled mind. Truly because a pure mind mostly arises by conditioning principle, whereas defilement arises relying on phenomena, it is specifically designated 'dust' in contrast to defilement. That which can cognize is called consciousness (vijñāna), because it cognizes the various objects. These eighteen are named 'realms' (dhātu) in the sūtras, and also named 'natures' (prakṛti/svabhāva). Realm differences are named realms; nature differences are named natures; because the natures of dharmas are distinct, they are called realms. (This concludes the first gate.)