The Threefold Body (Trikaya) of the Buddha is mentioned as Buddhahood; its representative theory is held by the Tendai School.

Every Buddha of Perfect Enlightenment is supposed to possess three bodies. Although the original names of Dharma-kaya, Sambhoga-kaya, and Nirmana-kaya mean literally ‘Principle-body,’ ‘Enjoyment-body,’ and ‘Transformation-body,’ the term ‘body’ in the ordinary sense is rather misleading because it conveys the idea of a bodily existence.

The Principle-body or Truth-body is the Ideal or the Principle or Truth itself without any personal existence. It is identical with the Middle Path Truth.

The Enjoyment- or Reward-body is the person embodied with real insight, i.e., the body attained as the value of a long causal action. It is twofold: (a) The body for self-enjoyment, i.e., the person when he is enjoying his own enlightenment. (b) The body manifested for the enjoyment of others, i.e., bodhisattvas above the primary stage of saintly perfection.

The Transformation-body is a body variously appearing to save people. It is also twofold: (a) The body exclusively for bodhisattvas of the primary stage that is a superior body of Transformation. (b) The body for those who are prior to the primary stage.

Every Buddha has these three aspects. While a Buddha represents the Principle or Truth which he himself has realized, he is, on the one hand, the realizer of the ideal or the enjoyer of his Enlightenment and, on the other hand, is the giver of the ideal or the deliverer of all who are suffering or perplexed. Thus the Buddha is viewed as the ideal (Enlightenment) itself, the enjoyer of it (the Enlightened), the giver of it to others (the Enlightener). The Enjoyment-body is obtained by the Buddha as a reward for long effort, while the Transformation-body is freely assumed by him in order to meet the needs of others and the world.

The Three Bodies of the Buddha are further divided into four, five, six or ten, but the above stated Threefold Body of the Tendai School may be regarded as the fundamental theory of Buddhahood.

It is not Buddhistic to seek the original principle or to consider the absolute as separate or independent. Here the Tendai School at once comes back to the ideation theory but expresses it somewhat differently. It is set forth that a conscious-instant or a moment of thought has 3,000 worlds immanent in it. This is a theory special to this school and is called ‘three thousand originally immanent,’ or ‘three thousand immanent in principle,’ or ‘three thousand immanent in nature – or sometimes ‘three thousand perfectly immanent.’ The immanency, either original, theoretical, natural or perfect, conveys one and the same idea; namely, that the one moment of thought is itself 3000 worlds. Some consider this to be the nearest approach to the idea of the Absolute, but if you consider the Absolute to be the source of all creation it is not exactly the Absolute. Or, it may be considered to be a form of ideation theory, but if one thinks that ideation manifests the outer world by the process of dichotomy it is quite different, for it does not mean that one instant of thought produces the 3,000 worlds, because a production is the beginning of a lengthwise motion, i.e., timely production. Nor does it mean that the 3 000 worlds are included in one instant of thought because an inclusion is a crosswise existence, i.e., spacely coexistence.

Although here the 3,000-world doctrine is expounded on the basis of ideation, it is not mere ideation, for all the dharmas of the universe are immanent in one thought-instant but are not reduced to thought or ideation.

That the world is immanent in one moment of thought is the philosophy of immanence, phenomena being identical with conscious action. It may be called ‘phenomenology,’ each phenomenon, matter or mind, expressing its own principle or nature.

The principle each phenomenon expresses is the triple truth of harmony (as void, as temporary and as mean), i.e., noumenon originally immanent, perfectly immanent, immanency in principle and immanency in nature. This means simply that a thing or being itself is the true state. Hence the phrase: “Everything, even the color or fragrance, is identical with the Middle Path, the Truth.”

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.

The ultimate truth taught n the Tendai School is Thusness (Tathata), not thisness (tattva). Thusness means the true state of things in themselves, the phenomenal world being the state of things manifested before us. The true state of things cannot be seen directly or immediately. We must see it in the phenomena which are ever changing and becoming. Thus the true state is dynamic. The phenomena themselves are identical with the true state of things. The true state of things is Thusness, i.e., things as they are manifested, just as moving waves are not different from the still water. We generally contrast the still water with the moving waves, but moving or staying they are only the manifestation of one and the same water. What is being manifested or shown outwardly is nothing but the thing itself. There is no difference between the two.

This is the theory of the true state of all dharmas; that is, all elements manifested are the elements in their own state (sarva-dharma-svalaksana-ta). Or. to use another expression, the ‘worldly state (phenomenal) is permanent’ (lokalaksana-nityata).

According to the Tendai doctrine any dharma expresses itself in all three truths. All existences are thus mutually penetrating in all three truths.