因明入正理論疏 2.42

2.42

述曰：第二文也。牒前因後指法云「此中所作性」者，是宗之法，能立因言。由是宗法，故能成前聲無常宗，名為因也。有故字者，前無今有，顯立因法，必須言故。不爾，便非標宗所以。前略指法，由此略無。前指法中指示二因；今唯牒一。前者欲顯同品定有，餘二言遍，三相異故，別顯二因；今略結指，故唯牒一。

The commentary says: This is the second text. Taking up the previous reason, it then points out the rule, saying, ''Being produced' here' is the property of the subject (pakṣadharmatā), the statement of the reason that proves. Because it is a property of the subject, it can prove the preceding thesis that sound is impermanent; hence it is called the reason. As for having the word 'because' (故): it was absent previously and is present now, showing that when stating a reason property, one must say 'because'. If not, it would not be the ground for presenting the thesis. Previously the rule was pointed out briefly, and thus it was omitted. In the previous pointing out of the rule, two reasons were indicated; now it takes up only one. Previously, wishing to show definite presence in the sapakṣa, the other two [characteristics] were said to be pervasive, and because the three characteristics differ, two reasons were separately shown; now it briefly concludes and indicates, and so only takes up one.