What is the connection between Shinto and Islam as if to suggest they came from a common religious source? I think we can be sure that they have no common religious source. But can we say this about Buddhism and the Upaniṣads? No we cannot. They have, you could say, a relationship or a connection, maybe because the overarching context they operate from is the same and very ancient. But I dare not say this in front of today’s Buddhists! Why is that?
To answer the foregoing question it should be obvious that Buddhism, in recent memory, has been somewhat of a magnet that draws agnostics, atheists and most, notably, irreligionists (those hostile to religion) to its temples and centers.
These types are usually westerners who lean heavily towards scientism; who don’t believe that man is, fundamentally, a spiritual creature just like a fish is an aquatic creature or a bird is a creature of the air. Man, for these types, is a seeker of pleasure but in modern life is not finding it as hoped in a sufficient amount. In fact, all that he finds is more and more daily displeasure and in some cases, downright suffering. So he thinks that he’d better look into Buddhism to help with his daily irritations which bring him nothing but displeasure. Maybe meditation would help.
And there you have it. Our modern day western Buddhist. But what is missing in this pop view of Buddhism? It is the very spiritual context of Buddhism, itself, that is missing which includes rebirth, karma and the pressing need to overcome samsara which is the repeating cycles of birth and death that individuals undergo without end unless they attain nirvana.
When you start comparing Buddhism with the Upaniṣads, contextually, they are very much the same. In other words, both share a common framework such that when you peel away the superficial veneer the same light, so to speak, illuminates them both. But this grand framework is nothing for the natural creature or better said, the biological creature. It is for the spiritual person, the ariya (S., ārya), that is, one who walks the spiritual path.
As we might expect, the Buddha was not an irreligionist. The Buddha, in fact, recognizes the existence of many kinds of gods such as Indra and Brahmā, for example. He was not a hater of gods but understood their place and their limitations (he spoke about some gods called ‘debauched in mind’ who only sought pleasure). This was also with the Upaniṣads. We should not forget that the first and second chapter of the Samyutta Nikaya (The Connected Discourses) are discourses with the gods (devatā) and the young gods (devaputta).
The Buddha shifted the notion of god as the one supreme god (who was not a creator god) to the attainment of nirvana which is beyond even the mental construct of a supreme god. In nirvana, any and all anthropocentric significance is superseded. This includes prayer and worship. This is not far from the Upaniṣads. Yajñavalkaya says, “Whereby everything reduces to Oneness, who then is left to worship whom?”
With the attainment of nirvana, man is no longer the measure of all things. Measurer and the measured return to the one source from which they first emerged. In fact, this is their absolute truth which transcends their former relative positions born of discrimination.
Understanding the role of self or atman in both Buddhism and Upaniṣads is to see different levels of self. What attaches to the human body of birth with all of its senses is a lower self. It is the self looking at the world from the perspective of the biological body of birth as this is who I am which would be the bodily person or sakkāyo. But there is another higher self who makes choices acting as a controller. This self decides to become, let’s say, a Buddhist. It does meditation rather than go out with the boys to have some beers. This is the protector or lord of the lower self which over identifies with the sakkāyo. Then there is the innermost self (praty-ātman) which attains nirvana in which the distinction between nirvana and self disappear. All this corresponds somewhat with the Upaniṣads in the forms of dehātman=sakkāyo; the jivatman= nātha self (protector or lord of self found in the Dhammapada); and paramatman (paccatta/praty-ātman).
The Upaniṣads speak of the pañcakoś or five sheaths which make up the bodily person, namely, the gross sheath, the breath sheath, the mind or manas sheath, the intellect sheath, and the bliss sheath. The five sheaths are said to be impermanent (anitya). This is not unlike Buddhism’s conditioned pañskandha or five aggregates which are never other than suffering and impermanent, that is, the bodily self (rūpa), the feeling self (vedana), the mental self (sañña), the volitional self (saṅkhāra), the self of consciousness (vijñāna). These selves are not who we really are. Of each one the Buddha says: this is not mine, this I am not, this is not my self. In this regard, we transcend the pañskandha. We realize our transcendent position by attaining nirvana in the very self (praty-ātman).
There are many other similarities but the important thing is that a relation exists between the Upaniṣads and Buddhism. The overarching context of both is that we can only escape from suffering by realizing the transcendent and no other way. As Dr. S. G. Deodikar point out in his book, Upaniṣads and Early Buddhism, “there is hardly any difference between original Buddhism and advaita of Upaniṣads. No wonder that in due course, Indian epics ranked the Buddha along with the other incarnations or avatārs of Viṣṇu.”