Brahman and Atman
Two concepts that are of paramount importance in the Upanishads are Brahman and Atman. The Brahman is the ultimate reality and the Atman is individual self (soul). Brahman is the material, efficient, formal and final cause of all that exists. It is the pervasive, genderless, infinite, eternal truth and bliss which does not change, yet is the cause of all changes. Brahman is “the infinite source, fabric, core and destiny of all existence, both manifested and unmanifested, the formless infinite substratum and from which the universe has grown”. Brahman in Hinduism, states Paul Deussen, as the “creative principle which lies realized in the whole world”.
The word Atman means the inner self, the soul, the immortal spirit in an individual, and all living beings including animals and trees. Ātman is a central idea in all the Upanishads, and “Know your Ātman” their thematic focus. These texts state that the inmost core of every person is not the body, nor the mind, nor the ego, but Atman – “soul” or “self”. Atman is the spiritual essence in all creatures, their real innermost essential being. It is eternal, it is ageless. Atman is that which one is at the deepest level of one’s existence.
Atman is the predominantly discussed topic in the Upanishads, but they express two distinct, somewhat divergent themes. Younger upanishads state that Brahman (Highest Reality, Universal Principle, Being-Consciousness-Bliss) is identical with Atman, while older upanishads state Atman is part of Brahman but not identical. The Brahmasutra by Badarayana (~ 100 BCE) synthesized and unified these somewhat conflicting theories. According to Nakamura, the Brahman sutras see Atman and Brahman as both different and not-different, a point of view which came to be called bhedabheda in later times. According to Koller, the Brahman sutras state that Atman and Brahman are different in some respects particularly during the state of ignorance, but at the deepest level and in the state of self-realization, Atman and Brahman are identical, non-different. This ancient debate flowered into various dual, non-dual theories in Hinduism.