瑜伽論記 4.225

4.225

順退分定，謂有鈍根；順住分定，謂有中根或利根性等者，此中但依四人成四故此說根，非依一人而成四種。下第十三說：四撿行經說依一人次第修故，道理亦有上根而下順退，亦有下根上順不退，其退分定退，其住分定與染心相入出，既不勝進亦不退下，順勝分定，定約別人修定，是利根，不與染心而相入出，第四亦爾，順決擇分定能生無漏，非勝分定。第十三說：四撿行經中順勝分定非退非住，唯是勝進非趣決擇故，決擇即分名決擇分，是支義類義。

Regarding "the concentration favorable to deterioration pertains to dull faculties; the concentration favorable to maintenance pertains to medium faculties or sharp faculties, etc.": here, the four are established based on four kinds of persons, which is why faculties are discussed in this way, rather than establishing the four kinds based on a single person. Below, in Fascicle 13, it says: the Sūtra on the Four Types of Conduct is explained based on a single person cultivating sequentially. In principle, there are also those with superior faculties who deteriorate downward, and those with inferior faculties who progress upward without deteriorating. Concentration favorable to deterioration deteriorates; concentration favorable to maintenance alternates in entering and emerging with defiled minds, neither advancing nor deteriorating; concentration favorable to distinction is definitively based on different persons cultivating concentration who have sharp faculties, and does not alternate in entering and emerging with defiled minds; the fourth is likewise. Concentration favorable to penetration can produce the taintless, and is not concentration favorable to distinction. Fascicle 13 says: in the Sūtra on the Four Types of Conduct, concentration favorable to distinction neither deteriorates nor maintains, but is solely superior progress, not heading toward penetration; penetration is itself the part, hence "part favorable to penetration" (nirvedha-bhāgīya), which means an auxiliary or category.