維摩經玄疏 5.85

5.85

答曰：若是真諦之理，即是思議之理；若是中道佛性之理，即是不思議之理。故此經云「如我病者，非真非假；眾生之病，亦不真不假」，故知中道之理，與真諦有異。真諦名思議理者，非如來藏也；以中道之理，名不思議者，即是如來藏也。無所積聚乃名為藏，故名不思議理也。

Answer: If it is the principle of the conventional truth, it is the conceivable principle; if it is the principle of the Middle Way buddha-nature, it is the inconceivable principle. Therefore, this sūtra says: 'Like my illness, which is neither real nor false; the illness of sentient beings is also neither real nor false.' Hence know that the principle of the Middle Way is different from the absolute truth. That the absolute truth is called the conceivable principle is because it is not the tathāgatagarbha; that the principle of the Middle Way is called the inconceivable is because it is precisely the tathāgatagarbha. It is called a 'storehouse' precisely because nothing is accumulated; therefore it is called the inconceivable principle.