俱舍論頌疏論本 2.18

2.18

釋曰：眼等五識有尋有伺，由與尋、伺恒共相應。謂眼等五識有二種因，故與尋、伺恒相應也。一行相麁、二外門轉，由此二因，故眼等識與尋、伺俱，其義決定，故說唯言。

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'.