Tendai presents itself as a grand synthesis of Buddhist doctrine and practice, gathered under the light of the Lotus Sutra. The Lotus Sutra is regarded as the Buddha’s final and complete revelation, the fullest expression of truth in which all earlier teachings are understood as expedient means, tailored to the capacities of beings yet ultimately converging in a single vehicle to Buddhahood. From this perspective, the diverse scriptures and doctrines of Buddhism are not contradictory, but different expressions of one underlying reality. This comprehensive vision encourages the study and integration of many teachings rather than the rejection of any particular strand.

At the heart of Tendai thought stands the doctrine of the Threefold Truth: emptiness, provisional existence, and the middle that holds both together. All phenomena are empty of independent self-nature, yet they also function provisionally in the world of experience, and the middle truth is the non-dual realization that these two aspects are inseparable. Closely related is the teaching of ichinen sanzen, “three thousand realms in a single thought-moment,” which describes how each moment of consciousness contains the full range of possible realms of existence, each realm mutually including the others. This vision of radical interpenetration undergirds the affirmation that all beings, in every condition, are intimately linked and capable of awakening.

Tendai further articulates the doctrine of original enlightenment, hongaku, which holds that all beings are inherently enlightened and that practice serves to uncover or realize this ever-present Buddhahood rather than to acquire something new. This universal Buddhahood is extended even to insentient beings such as plants and stones, so that the entire natural world is seen as participating in the field of enlightenment. Such a view dissolves rigid boundaries between sacred and profane, sentient and insentient, and encourages a profound reverence for all forms of existence.

In terms of practice, Tendai is marked by an inclusive and integrated approach. Meditation is systematized in the four kinds of samadhi—constantly sitting, constantly walking, half-walking and half-sitting, and neither walking nor sitting—alongside the classic union of calming and insight. Ethical discipline through bodhisattva precepts, devotion to the Lotus Sutra, and veneration of Buddhas and bodhisattvas are all embraced. Esoteric elements such as mantras, mandalas, and ritual are incorporated and harmonized with exoteric teachings, so that contemplative, devotional, ethical, and ritual dimensions are woven into a single path oriented toward the realization of the one vehicle of Buddhahood for all beings.