The whole universe is said to have the constituency of ‘three thousands,’ but the theory is quite different from other pluralistic systems. It is not an enumeration of all dharmas; nor is it the world system of three Chiliocosms. What is it then? We must explain these ‘three thousands.’ The expression ‘three thousands’ does not indicate a numerical or substantial immensity, but is intended to show the inter-permeation of all dharmas and the ultimate unity of the whole universe.

As the basis of ‘three thousands’ the Tendai school sets forth a world system of ten realms. That is to say, the world of living beings is divided into ten realms, of which the higher four are saintly and the lower six ordinary.

1. The realm of Buddhas. A Buddha is not inside the circle of ten, but as he advents among men to preach his doctrine he is now partially included in it.
2. A bodhisattva: a would-be-Buddha.
3. Pratyeka-buddha: a Buddha for himself, not teaching others.
4. Sravaka: a direct disciple of the Buddha. The above four are classed as the saintly stages.
5. Heavenly Beings: superhuman as they are, they cannot get perfectly enlightened without the teaching of the Buddha.
6. Asura: fighting spirits. Though partially heavenly, they are placed in the lower half of the realm.
7. Men: neutral in nature.
8. Preta: departed beings, otherwise called ‘hungry spirits.’
9. Beasts: innocent in nature, including the whole animal kingdom.
10. Depraved men: ‘hellish beings’ who are in the lowest stage.

These ten realms are mutually immanent and mutually inclusive, each one having in it the remaining nine realms. For example, the realm of men will include the other nine from Buddha to Hell, and so will any of the ten realms. Even the realm of Buddhas includes the nature of hell and all the rest, because a Buddha, though not hellish himself, intends to save the depraved or hellish beings, and therefore also has hell in his mind. In this sense, the realm of the Buddhas, too, includes the other nine realms.

This immanence of each of the ten worlds in all of them accounts for 100 worlds. Further, each of these realms has ten different features as we have seen above, i.e., form, nature, substance, force, action, cause, circumstance, effect, remuneration and the ultimate state. These are the ten features of Thusness. By discovering these ten features in the 100 worlds, this school arrives at the doctrine of 1,000 realms.

Moreover, each realm consists of three divisions: the species of living beings, the species of space-region or vessel to live in and the species of five aggregates (skandhas) taken separately from living beings—form (matter), perception, conception (idea), volition (will) and consciousness. Thus there are three thousand realms, constituting the whole of manifested reality.

In Buddhism, ‘three thousands’ usually refers to the great Chiliocosm consisting of 1,000 small, 1,000 middle, and 1,000 large worlds. With the Tendai School, however, it is not such a world system, but is the universe of all beings and things, i.e., the whole world of dynamic becoming.