釋摩訶般若波羅蜜經覺意三昧 1.18

1.18

答曰：攬而可別名為相。心識之法既無形質，若不約此四運之念分別，則難可了知，若不可了知，則不可觀察，故須先以四相分別。若觀分明了達此相非相，即入一相平等。

Answer: That which can be grasped and distinguished is called a "characteristic." Since the phenomena of mental consciousness are devoid of physical shape and substance, if they are not distinguished with reference to the thoughts of these four movements, they will be difficult to understand. If they cannot be understood, they cannot be observed; hence one must first distinguish them by means of the four characteristics. If in contemplating them one clearly and thoroughly realizes that these characteristics are non-characteristics, one immediately enters the equality of the single characteristic.