俱舍論頌疏論本 2.18

2.18

Explanation: The five consciousnesses, such as the eye, have investigation and have analysis because they are always associated with investigation (vitarka) and analysis (vicāra). That is to say, the five consciousnesses, such as the eye, have two causes for always being associated with investigation and analysis: first, their mode of activity is coarse; second, they operate through external gates. Due to these two causes, the consciousnesses of the eye and the rest are accompanied by investigation and analysis; this principle is fixed, and therefore the verse says 'only'.