成唯識論了義燈 7.72

7.72

或言總意別，意取四十心滿修四善根，文言略故，但云四十心。

Or else, the expression is general while the meaning is specific: the intent takes the completion of the forty mental states as the cultivation of the four roots of goodness, and because the text is abridged, it simply says "forty mental states."