[I]n the discourse of the Substance, [Chih-i] uses three analogies to distinguish correct or one-sided substance, from which he intends to imply that the Triple Dimension of Buddhism is embraced by the correct substance, namely, Teaching is reflected by the first analogy; Practice by the second one; and Realization by the third one.

The first analogy is concerned with three kinds of animal (a rabbit, a horse, and a big elephant) going across the river. The rabbit and the horse are not so strong, and thus, they swim through water without penetrating its depth, or without reaching the bottom (even though all of them reach the other shore). The rabbit and the horse analogize the Two Vehicles (śrāvakas and pratyekabuddhas). The water analogizes emptiness, and the bottom analogizes no-emptiness. Since the Two Vehicles have less knowledge and cannot penetrate deeply to reach the bottom, they can only perceive emptiness but cannot perceive no-emptiness. The big elephant is strong and can reach the bottom. This analogizes the bodhisattva, for the bodhisattva, whose knowledge is profound, can not only perceive emptiness but also no-emptiness. In the case of touching the bottom, there are two levels that symbolize the perception of the Separate Teaching, and that of the Perfect Teaching in terms of the Ultimate Truth. The bottom, in this case, is also the analogy for the Ultimate Truth. In the procedure of reaching the other shore, the small elephant can only touch the mud in the bottom, which analogizes that, even though the bodhisattva can perceive no-emptiness, this knowledge of the Separate Teaching is still not the ultimate. The big elephant that can penetrate deeply to the firm ground in the bottom analogizes that this perception of no-emptiness with the knowledge of the Perfect Teaching is ultimate. From the dimension of the Teaching, this analogy singles out the knowledge of the Perfect Teaching that contains the Ultimate Truth as the only substance. (page 112-113)