因明入正理論疏 1.22

1.22

七問：「何故不名果明，但名因明？」答：「果有果之明，非果皆即明。因有因之明，是因皆即明。果明不定，義亦有濫。因明兩定，義亦無濫，故名因明。本欲以因成果義故，不欲以果成因義故。」

Seventh question: "Why is it not called the illumination of the fruit (phalavidyā), but only named hetuvidyā?" Answer: "A fruit has its illumination of fruit, but not every fruit is itself an illumination. A cause has its illumination of cause, and every [such] cause is itself an illumination. The illumination of the fruit is undetermined and its meaning would also be confused. The illumination of the cause is determined in both respects and its meaning is without confusion; therefore it is named hetuvidyā. This is because one originally intends to use the cause to establish the meaning of the fruit, not to use the fruit to establish the meaning of the cause."