Question: How do you know this?
Answer: It is stated in the Sutra of Infinite Meaning, "At the beginning the teaching of the Four Noble Truths was preached in Agama sutras ..., the Hodo sutras were preached next." The Nirvana Sutra also states, "The Hodo sutras were preached after the Agama sutras were."
Question: Hodo is an Indian term meaning Mahayana in Chinese and Japanese. The Flower Garland, Wisdom, Lotus and Nirvana Sutras all belong to the Mahayana Hodo sutras. Why do you then call only those sutras preached in the Hodo period the Hodo sutras?
Answer: In fact, not only sutras of the Hodo period are considered Hodo sutras but also Mahayana sutras as the Flower Garland Sutra, Wisdom Sutra, and Lotus Sutra also belong to this category. Nevertheless, these are clear reasons why only those teaching preached during Hodo period are called the Hodo sutras. Precedents for this can clearly be found in the Sutra of Infinite Meaning and the Nirvana Sutra. The enlightenment preached in the Agama sutras is strictly of the Hinayana teaching. The Buddha then preached the Mahayana teachings beginning with the Hodo sutras. The teachings from the Hodo sutras onward then are all considered Mahayana. However, since the teachings in the Hodo sutras are the beginning of the Mahayana teachings, there are called Hodo to distinguish these teachings from those preached after. For instance, when the Discourse on the Repository of Abbidharma Discussions analyzes cognition into eighteen elements, although only ten and a half of the eighteen are of matter, while the remaining seven and a half element are mind, they are called realms of matter because they begin with matter.