P’o-san Hsien-i (Refuting the three and revealing the one) is the function associated with the Subtlety of Knowledge. Given that the Three Vehicles (Śrāvaka, Pratyekabuddha and Bodhisattva) mistake the three teachings (Tripiṭaka, Common and Separate) that are designed for them as the Ultimate Truth and become attached to these teachings, the Buddha felt that it is necessary to destroy their attachment in order to reveal the knowledge of the Buddha as the One Vehicle. Therefore, by introducing the one ultimate Buddha-vehicle, the Three Vehicles are prevented from being attached to the three teachings. The refutation and the revelation are associated with the function of the Buddha’s knowledge. Without this function, the Relative Truth of the Three Vehicles and the Ultimate Truth of the One Buddha-vehicle will not be known. (Vol. 2, Page 444)