維摩經玄疏 5.137

5.137

三、類通三種佛性者：一，正因佛性；二，了因佛性；三，緣因佛性。《大涅槃經》云：「言佛性者，亦一亦非一，非一非非一。」亦一者，正因，真正解脫也；非一者，緣因佛性，方便解脫也；非一非非一者，了因佛性，即是實慧解脫也。

Third, analogously correlating the three kinds of buddha-nature: first, the buddha-nature as direct cause; second, the buddha-nature as revealing cause; third, the buddha-nature as conditioning cause. The Mahāparinirvāṇa Sūtra states: 'As for the buddha-nature, it is both one and not one, neither not one nor not not-one.' 'Both one' is the direct cause, true liberation; 'not one' is the buddha-nature as conditioning cause, the liberation of expedient means; 'neither not one nor not not-one' is the buddha-nature as revealing cause, which is the liberation of real wisdom.