The central theory of the three schools of thought is the doctrine of the middle way, which takes the nonexistent middle way as the essence of the world. Specifically, it is divided into two truths and eight not-in-the-middle theories. The second really refers to the true meaning and the vulgar meaning. The true meaning is the truth of Buddhism, all laws are empty, and the vulgar meaning is the secular truth, and all laws are available. On the basis of two truths, Ji Zang put forward the theory of four truths. The first is truth and vulgarity; Secondly, the general truth is that there is also time, which really means that there is neither time nor time; Third, the second is vulgar reason, and the second is true meaning; Fourth, the truth that the first three words can express is vulgar, and the incredible realm that cannot be expressed is the true meaning. The second truth was originally intended to facilitate the hypothesis of speaking and education, and the purpose was to persist. Four fold and two truth emphasize the realm of no income. Eight does not mean discussing the meaning of the middle way from four aspects: entity, time, space and movement. It has the idea of "never being born or dying, never being different, never coming or not going", which is used to break the evil and clear the right, that is, to break all kinds of prejudices held by ordinary people and show the reality of the middle way in an all-round way. This doctrine of the mean is also the Buddhist theory of the three schools. From the middle point of view, there is no Buddha and no sentient beings without income, but from the perspective of the world, there are both Buddhas and sentient beings, and all sentient beings have Buddha nature, but they cannot become Buddhas because of infatuation. All sentient beings, as long as their thoughts conform to the mean, can become Buddhas immediately, while all dull-rooted sentient beings need a long time to become Buddhas.