Buddha's omniscience

The Buddha stated that it is not possible to be all-knowing all at once.

That means it is possible for the Buddha to know and understand all things if he tried to learn it, but not simultaneously. This means he has the capacity (the intelligence) to know all things, but it doesn't mean that he indeed knew all things.

From MN 90:

Then the king said to the Buddha, “I have heard, sir, that the ascetic Gotama says this: ‘There is no ascetic or brahmin who will claim to be all-knowing and all-seeing, to know and see everything without exception: that is not possible.’ Do those who say this repeat what the Buddha has said, and not misrepresent him with an untruth? Is their explanation in line with the teaching? Are there any legitimate grounds for rebuke and criticism?”

“Great king, those who say this do not repeat what I have said. They misrepresent me with what is false and untrue.” ....

Then the king said to the Buddha, “Sir, might the Buddha have spoken in reference to one thing, but that person believed it was something else? How then do you recall making this statement?”

“Great king, I recall making this statement: ‘There is no ascetic or brahmin who knows all and sees all simultaneously: that is not possible.’”

“What the Buddha says appears reasonable.

But what kind of knowledge does the Buddha definitely possess? According to MN 71 quoted by santa100, he definitely possessed the three knowledges, and at the same time he denied complete omniscience.

As for knowledge apart from the three knowledges, the Buddha possessed the capacity to know and understand them, but he does not know them all at once.

However, much later tradition exaggerated the claims of the Buddha's omniscience, for e.g. Mil 6.2.8 and Mil 3.6.2. The Milindapanha was authored 400 to 700 years after the Buddha's passing away.

In Mil 6.2.8, Ven. Nagesena was asked why did the Buddha introduce the monastic rules little by little rather than altogether at once, since he was omniscient. He answered that although the Buddha knew all the monastic rules from the beginning, he did not want to scare people with too many rules, so he introduced new rules only when they were needed.

In Mil 3.6.2, Ven. Nagesena was asked the same question, but here he answered that a physician dispenses medicine only after the disease shows symptoms, even if he knew how to treat all diseases.

Mil 6.2.8 and Mil 3.6.2 make the same kind of excuses that was ridiculed in MN 76 (quoted below). So, I feel that it is not good to unnecessarily exaggerate claims about the Buddha, as it will put off intelligent people from learning the Buddha's teachings.

“Sandaka, take a certain teacher who claims to be all-knowing and all-seeing, to know and see everything without exception, thus: ‘Knowledge and vision are constantly and continually present to me, while walking, standing, sleeping, and waking.’ He enters an empty house; he gets no alms-food; a dog bites him; he encounters a wild elephant, a wild horse, and a wild cow; he asks the name and clan of a woman or man; he asks the name and path to a village or town. When asked, ‘Why is this?’ he answers: ‘I had to enter an empty house, that’s why I entered it. I had to get no alms-food, that’s why I got none. I had to get bitten by a dog, that’s why I was bitten. I had to encounter a wild elephant, a wild horse, and a wild cow, that’s why I encountered them. I had to ask the name and clan of a woman or man, that’s why I asked. I had to ask the name and path to a village or town, that’s why I asked.’

A sensible person reflects on this matter in this way: ‘This teacher makes such a claim, but he answers in such a way. This spiritual life is unreliable.’ Realizing this, they leave disappointed.

The Buddha knew everything about what was essential to know. The Pali suttas say:

11. Those who mistake the unessential to be essential and the essential to be unessential, dwelling in wrong thoughts, never arrive at the essential.

12. Those who know the essential to be essential and the unessential to be unessential, dwelling in right thoughts, do arrive at the essential.

Dhammapada

Here, ruler of gods, a bhikkhu has heard that nothing is worth adhering to. When a bhikkhu has heard that nothing is worth adhering to, he directly knows everything; having directly known everything, he fully understands everything; having directly known everything, he fully understood everything...

MN 37

On one occasion the Blessed One was dwelling at Kosambi in a siṃsapa grove. Then the Blessed One took up a few siṃsapa leaves in his hand and addressed the bhikkhus thus: “What do you think, bhikkhus, which is more numerous: these few siṃsapa leaves that I have taken up in my hand or those in the siṃsapa grove overhead?”

“Venerable sir, the siṃsapa leaves that the Blessed One has taken up in his hand are few, but those in the siṃsapa grove overhead are numerous.”

“So too, bhikkhus, the things I have directly known but have not taught you are numerous, while the things I have taught you are few. And why, bhikkhus, have I not taught those many things? Because they are unbeneficial, irrelevant to the fundamentals of the holy life, and do not lead to revulsion, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbāna. Therefore I have not taught them.

“And what, bhikkhus, have I taught? I have taught: ‘This is suffering’; I have taught: ‘This is the origin of suffering’; I have taught: ‘This is the cessation of suffering’; I have taught: ‘This is the way leading to the cessation of suffering.’ And why, bhikkhus, have I taught this? Because this is beneficial, relevant to the fundamentals of the holy life, and leads to revulsion, to dispassion, to cessation, to peace, to direct knowledge, to enlightenment, to Nibbāna. Therefore I have taught this.

SN 56.31

Generally [not particualrly] Theravadin speak of an all-knowingness that has little to do with the omniscient mind as presented by Mahayana teahcings.

A short 'definition' of omniscience, given by Geshe Gyaltsen:

The 'ultimate consciousness' that is the direct realization of emptiness and the 32 qualities - the ten powers, four fearlessness and eighteen unshared qualities - are parts of the omniscience, that is, they are omniscience. The 32 qualities are 32 branches of omniscience.

It means in particular, as found in Gyaltsab Je's commentary of the sublime continuum, Geshe Gyaltsen's teachings on this and on Tsongkhapa's Special Insight chapter of the Middle-Length Lam Rim:

• the omniscient mind of a buddha is free from all defilements - free from the two obscurations - and thus its suchness is called 'suchness without defilements' (nature truth body)
• the omniscient mind of a buddha is the only one mind that realizes the two truths (or 'the mode and varieties') directly simultaneously. Whenever cnventionalities appear to a sentient being, they appear together with the appearance of true existence because sentient beings have not abandoned knowledge obscurations (even a bodhisattva on the tenth bhumi). A buddha is the only being free from this [type of] dualistic appearance
• the omniscient mind of a buddha is free from conceptualization (and thus unmistaken)
• the omniscient mind of a buddha knows all existent of the three times
• the omniscient mind of a buddha realizes its object newly, that is by its own power
• the omniscience knows all the different aspects of each of the disciples.

Omniscience is the 'wisdom truth body', one the two bodies of the dharmakaya. While the 'naturally abiding linage' (suchness with defilements) is that which is suitable to become the 'nature truth body', the 'developmental linage' is that which is suitable to become the 'wisdom truth body', the omniscient mind of a buddha.

Before actualizing fully qualified special insight, calm abiding and special insights are two different mind. At the fourth preparation on the access level, there is a union of calm abiding and special insight, whereby they become one and the same mind. In a similar fashion, the omniscient mind of a buddha is a non-conceptual great compassion, a non-conceptual bodhicitta, the exalted wisdom, etc. as one and the same mind.

Omniscience is discussed at length in:

1. Texts on Buddha nature, such as Maitreya’s Sublime Continuum: The Essence of a One Gone Thus, with Commentary by Gyaltsap Darma Rinchen, and so forth.
2. Tsongkhapa's Middle-Length Lam Rim or Great Lam Rim, chapter on Special Insight.
3. Maitreya's Ornament of Clear Realization: A Commentary on the Prajnaparamita.

Omniscience or Sabbannuta Nana is one of six knowledges exclusive to a Sammasambuddha:

A Supreme Buddha possesses 6 kinds of knowledge not shared by others. These Incomparable Qualities are:

1. Asaya-anusaya Nana: Knowledge of the inclinations and latent/inherent tendencies of all beings.
2. Indriya-paropariyatti Nana: Knowledge of the mental faculties and their state of maturity in all beings.
3. Sabbannuta Nana: Knowledge of Omniscience and Omnipotence.
4. Anavarana Nana: Knowledge of penetrative clarity without obstruction i.e. unrestricted access to any objective field.
5. Yamaka Patihariya Nana: Knowledge of the Twin Miracle.
6. Maha Karuna Samapatti Nana: Knowledge of the attainment of Great Compassion by which He looks at the world

It means the ability to understand anything he sets his mind on, both in worldly sense and in ultimate reality. It works in association with another Nana called the Anavarana Nana, which is also one of the six. It means the knowledge of penetrative clarity without obstruction or unrestricted access to any objective field.

Omniscience is understood differently depending on one's school, capacity, and progress.

• a primitive ("hinayana") understanding, is that omniscience literally means simultaneously knowing all facts about everything.
• an orthodox Theravada explanation (as far as I understand it), is that omniscience is Buddha's unlimited/unobscured capacity to completely and properly understand/analyze anything and correctly reason about anything the Buddha adverts to or wishes to know. In modern terms this can be explained as a genius ad-hoc wit. In this view Buddha is somewhat like a super Sherlock Holmes who can deduce facts about people or events by noting and connecting even the smallest evidence. Particularly, this could be seen in Buddha's seeming ability to read people's minds or to know more about their lives than they publicized - and therefore to give customized guidance tailored to their perspective.
• one Mahayana explanation, is that omniscience is direct insight into the true nature of things (referred to, but not exhaustively explained by, the term "emptiness"). To give a modern metaphor, Buddha knows how the videogame of life works, and even though he might not have literally visited all the infinite computationally generated universes, he has fully understood the principles by which the game works - and so in this sense there is nothing principally new in this videogame that he does not know. He knows the extent of what's possible, what's impossible, he clearly sees the winning strategy as well as the various false strategies that people pursue. Because of omniscience, playing the game is no longer fun for the Buddha but out of compassion Buddha stays in the game to help others.
• a more advanced Mahayana perspective, is that omniscience is nothing other than prajna-paramita - which kind of subsumes both of the above. For more details see Conze's Large Sutra on Perfect Wisdom.

Some quotes and research on Buddha's omniscience are available here and here.

In MN 71, the Buddha clarifies the meaning of his omniscience to the wandering ascetic Vacchagotta:

Vaccha: ‘Venerable sir, I have heard this said: The recluse Gotama is all knowing and all seeing and acknowledges remainderless knowledge and vision in this manner, ‘while walking, standing, lying or awake, constantly and continually knowledge and vision is established, to me’.Venerable sir, those who say, these words, ‘The recluse Gotama is all knowing and all seeing and acknowledges remainderless knowledge and vision:while walking, standing, lying or awake, constantly and continually.’ Are they saying the words of good Gotama and are they not blaming the Blessed One falsely?

The Buddha: Vaccha, those who say, the recluse Gotama is all knowing and all seeing and acknowledges remainderless knowledge and vision, while walking, standing, lying or awake, constantly and continually. They, do not say my words, they blame me falsely.

Vaccha: Venerable sir, saying how would it be said, correctly not blaming the Blessed One falsely?

The Buddha: ‘The recluse Gotama knows the three knowledges. Saying it thus they would be saying the right thing, and not blaming me falsely. Vaccha, whenever I desire, I recollect the manifold previous births, such as one birth, two births, with all modes and all details, thus I recall the manifold previous births. Vaccha, when I desire, with the purified heavenly eye beyond human, see beings disappearing and appearing, in unexalted and exalted states, beautiful and ugly, in good and bad states,-- I see beings, according their actions. Vaccha, destroying desires, my mind released and released through wisdom, here and now by myself realising I abide. Vaccha, if it is said, the recluse Gotama knows the three knowledges, saying it thus, you would be saying the right thing and not blaming me falsely’.

Ven. Bodhi further elaborates by citing the Commentary in his note in "The Middle Length Discourses":

MA explains that even though part of the statement is valid, the Buddha rejects the entire statement because of the portion that is invalid. The part of the statement that is valid is the assertion that the Buddha is omniscient and all-seeing; the part that is excessive is the assertion that knowledge and vision are continuously present to him. According to the Theravāda exegetical tradition the Buddha is omniscient in the sense that all knowable things are potentially accessible to him. He cannot, however, know everything simultaneously and must advert to whatever he wishes to know. At MN 90.8 the Buddha says that it is possible to know and see all, though not simultaneously, and at AN 4:24/ii.24 he claims to know all that can be seen, heard, sensed, and cognized. This is understood by the Theravāda commentators as an assertion of omniscience in the qualified sense. See too in this connection Miln 102–7.