Saichō’s most innovative classification systems were devoted to revealing the differences between the practices advocated by the various Buddhist schools. One of the most important of these systems was based on a hierarchical classification of five types of bodhisattva found in the Pu pi ting ju ting ju yin Ching (Niyatāniyatagatimudrāvatārasūtra). Each type was compared with a man who was attempting to travel to a distant place. If the man boarded the wrong type of vehicle, he would never arrive at his destination because winds and storms would constantly delay him and force him to turn back. If he chose a more suitable vehicle, he would eventually arrive at his destination, but only after a very long period of time. If he rode the best vehicle, he would quickly arrive at his destination. The five types of bodhisattvas described in the sūtra and their vehicles were:

1. 1. The bodhisattva who followed sheep vehicle practices (yōjōgyō)
   2. The bodhisattva who followed elephant vehicle practices (zōjōgyō)
   3. The bodhisattva who followed the practices of the vehicle which endowed him with superhuman powers enabling him to reach the sun and moon (gatsunichi jinzū jōgyō)
   4. The bodhisattva who followed the practices of the vehicle which endowed him with the superhuman powers of a Śrāvaka (shōmon jinzū jōgyō)
   5. The bodhisattva who followed the practices which endowed him with superhuman powers like those of the Buddha (Nyorai jinzū jōgyō)

The sūtra did not describe the actual practices which each vehicle represented. Rather, the main theme of the sūtra was that not all religious practices were of the same efficacy. Some practices enabled a person to advance rapidly towards his religious goal without any danger of backsliding. Others, especially Hinayāna practices, caused him to regress, removing him further away from his goal than ever. Although the sheep vehicle and the elephant vehicle were both subject to backsliding, the other three vehicles were not.

In his writings Saichō frequently mentioned traditional Tendai classifications of Buddhist doctrine, such as the division of the Buddha’s teaching into five periods and eight types of teaching (goji hakkyō). In addition, he developed a number of new systems of classification which were designed to reveal various aspects of the superiority of Tendai teachings over those of other schools. Even before studying in China, Saichō had divided Buddhist schools into two categories, those based on sūtras (the words of the Buddha) and those based on Sāstras (works by Buddhist monks). Using this classification, Saichō criticized the two preeminent Buddhist schools in Japan, the Hossō and Sanron, because they were based on works (sāstras) by Buddhist monks rather than on the words of the Buddha. Twenty years later in the Hokke shūku he further refined this system by dividing the schools based on sūtras into two groups: the Tendai School, which was based on the Lotus Sūtra, and all other schools based on sūtras, such as the Kegon School.

Saichō’s view of the Perfect faculties of the Japanese people was partly based on statements in the Lotus Sūtra that the Buddha’s supreme teaching could be preached during the “latter evil age.” Saichō believed that the faculties of the Japanese people had matured and that they were ready to hear him expound the Buddha’s ultimate teaching found in the Lotus Sūtra. Although the Sanron and Hossō interpretations of the Lotus Sūtra had been studied previously in Japan, Saichō argued that they did not represent the correct interpretation of the Lotus Sūtra. The Tendai teachings concerning the Lotus Sūtra, transmitted directly to Saichō by Chinese T’ien-t’ai masters, were the only explanations of the sūtra which fully revealed it as the Buddha’s ultimate teaching. In order to stress this point, Saichō often referred to his school as the Tendai Hokkeshū (Lotus School), and thus closely linked the terms Tendai and Lotus Sūtra.

Chien-chen had brought the first T’ien-t’ai texts to Japan, but had not actively attempted to spread Tien-t’ai teachings. Instead, he had devoted himself to conducting Ssufen lü ordinations. As a result T’ien t’ai teachings were virtually forgotten several decades after Chien-chen’s death. In contrast, Saichō succeeded in spreading T’ien-t’ai teachings throughout Japan. By Saichō’s time the faculties of the Japanese people had matured. They were ready to listen to the Tendai interpretation of the Lotus Sūtra.

Saichō used the concept of the maturing of people’s faculties in a different way than Chih-i. Rather than applying the idea to individuals, Saichō argued that the Japanese people as a group possessed mature faculties. Saichō utilized Japan’s place in Buddhist history and the teachings concerning the decline of Buddhism to support his views. In the preface to the Ehyō Tendaishū dated 816, Saichō first presented this idea in several enigmatic, short sentences:

“In Japan the Perfect faculties (enki) of the people have already matured. The Perfect teaching has finally arisen.”

Several years later in his Shugo kokkaishō, Saichō further explained his view:

Now men’s faculties have all changed. There is no one with Hinayāna faculties. The Period of the True and of the Imitated Dharma have almost passed, and the age of mappō is extremely near. Now is the time for those with faculties suitable for the Hokke One-vehicle teaching. How do we know this? Because of what the Anrakugyōbon [Peaceful Practices chapter of Lotus Sutra] teaches about the latter days of the decline of the Dharma.

Chih-i categorized the maturation of man’s faculties and subsequent enlightenment in three stages. First, the karmic seeds connecting a person to Buddhism had to be planted (geshu). Although everyone possessed the Buddha-nature, a person first had to be exposed to the Buddha’s teachings in order to begin to realize this basic truth. He had to listen to elementary teachings which gradually drew him on to more profound teachings until his faculties matured (jōjuku). In the second stage, his faculties had matured and he was ready to hear the Buddha’s ultimate teaching, the Lotus Sūtra. Finally, in the last stage, the process was completed; freed (gedatsu) from his sufferings, he had achieved perfect enlightenment. For Chih-i this system was to be applied on an individual basis. One person might be at an advanced stage, while his neighbor might be at a lower stage.

One of the central teachings of the Lotus Sūtra is that during most of his life the Buddha preached expedient teachings for those with lesser faculties, but waited until the faculties of people had matured sufficiently before he preached his ultimate teaching, the Perfect teaching of the Lotus Sūtra, at the end of his life. As Saichō stated in the Hokke shūku, “The basic teaching of the One-vehicle (is not preached) until the proper time has arrived and (the audience) has the proper faculties. Only when their faculties have matured and the appropriate time has come does the Buddha preach it. Thus the Buddha waited until the Sudden faculties (tonki) of people had matured before preaching the One-vehicle Sudden Teaching.”

If a religious teaching is to be effective, it must be suited to the abilities and faculties of those to whom it is preached. If it is too profound for its listeners, they may be frightened by it and thus doubt their own abilities, or they may leave the assembly at which it is being preached. Even the earliest sūtras contain the idea that the Buddha adapted his teachings to fit the capabilities of his audience. The Buddha was often compared to a doctor who administered medicine to the sick. If the medicine (or doctrine) was not suited to their needs, it would not cure them. The Lotus Sūtra and the Hua yen Ching (Avatamsakasūtra) both contain passages which describe Śrāvakas and pratyekabuddhas who did not have faculties sufficiently mature to understand the Buddha’s more advanced teachings. These passages played key roles in Chih-i’s systems of classification of Buddhist teachings. The Hua yen Ching was criticized because it made no allowances for the faculties of its listeners. It was thus considered an ineffective teaching for most people, leaving them as if they were ‘deaf and dumb.’ The Lotus Sūtra, in contrast, did consider the faculties of its audience. According to the Lotus Sūtra, the Buddha waited until his listeners were ready to hear his ultimate teaching before preaching the Lotus Sūtra. Despite this, five-thousand people left the assembly at which the Buddha preached the Lotus Sūtra because of their “overweening pride.” On the basis of this passage, Chih-i was able to argue that the Nieh p’an Ching (Mahāparinirvāpasātra), traditionally regarded in China as the Buddha’s last sermon, had the function of saving these five-thousand monks and nuns. Chih-i thus classified the Nieh p’an Ching in the same period of the Buddha’s life as the Lotus Sūtra and noted that the Nieh p’an Ching included elements if the Perfect Teaching.