俱舍論頌疏論本 1.139

1.139

釋曰：成第六依故者，立意界所由也。眼等五識各有別依，謂眼等五根。第六意識無別所依，為成此依，故立意界。十八界應知者，結成十八界也。既立意界，由此六識各有所依，成十八界，所依、能依境界各六故，成十八界。所依六者，謂眼等六根。能依六者，謂眼等六識。境界六者，謂色等六境。

The commentary says: "To establish the basis of the sixth" gives the reason for establishing the mind element. The five consciousnesses, the eye[-consciousness] and the rest, each have their distinct basis, namely the five sense faculties, the eye and the rest. The sixth, mental consciousness, has no distinct basis; in order to establish this basis, the mind element is established. "The eighteen elements should be known" concludes the establishment of the eighteen elements. Once the mind element is established, because the six consciousnesses each have their respective basis, the eighteen elements are established; since there are six each of bases, based [consciousnesses], and cognitive objects, the eighteen elements are established. The six bases are the six faculties, the eye and the rest. The six based [consciousnesses] are the six consciousnesses, the eye[-consciousness] and the rest. The six cognitive objects are the six fields, visible forms and the rest.