The Upanishads are driven by their inner thought to give some grounds for such assertions. Yet there is no attempt at logical speculation and demonstrative reasoning. The intuitive affirmations surge forth with the reality of the living faith of one describing an experience which he himself has had. They affirm that this ultimate reality cannot be grasped by learning or reasoning.
It reveals itself only in our heart through sublime purity, absolute self-control, self-abnegation, and cessation of mundane desires. Man not only becomes moral in his relations to his fellow beings, but becomes super-moral, as it were, by an easy control of the conflicts of his lower instincts and desires, and by superior excellence of character. It becomes possible for him to merge himself in an intuitive contact with the transcendental spiritual essence with which he can immediately identify himself.
The Upanishads again and again reiterate the fact that this spiritual essence is in cognizable by any of the sense-organs-by eye or by touch-that it is beyond the reasoning faculties of man and is therefore unattainable by logic, and that it is indescribable in speech and unthinkable by thought.
The apperception of it is not of an ordinary cognitive nature, but is an apperception of the essence of our beings; and, just as external nature was regarded as being held and maintained in Brahman, so the totality of our being, our sense- functions, and thought-functions were regarded as having come out, being held and sustained in this inner being.
It was also regarded as the Antar-yamin or the inner controller of our personality-the spiritual entity which is its root and in which lie sustained and controlled all our vital activities and cognitive and conative functions.
We can have an apperception of it only when we transcend the outer spheres of ordinary life and penetrate into the cavern oil which neither the physical luminaries nor the luminaries of thought and sense shed any light. Yet it is a light in itself, from which all other lights draw their illumination. It is subtle and deep, and reveals itself only to those who attain that high spiritual perfection by which they transcend the limits of ordinary personality.
We find anticipations of doubt as to the possibility of such a subtle essence, which was our inmost being, becoming identical with the highest reality of the universe from which everything else emanated. Various parables are related, in which attempts are made to prove the existence of a subtle essence which is unperceived by the eye. In the parable of the banyan tree we are told how the big tree can reside inside a grain-like seed.
In another parable it is shown that the salt which is invisible to the eye can be tasted in every drop of saline water. We have also the parable by which Prajapati instructed Virochana and Indra how two different states of the self can be distinguished from the corporeal body, the dream self and the dreamless self, and how it is the self of the deep dreamless sleep that displays the nature of the eternal unthinkable within us.
The deep dreamless sleep brings us into daily contact with the eternal self within us, which is dissociated from all changes, and which forms the essence of our whole being. In the dialogue between Yama and Nachiketas, when the latter seeks instruction regarding the fate of men at death, he is told that when inquiry is earnestly made the true self in man is discovered to be eternally abiding, and can be grasped only through spiritual contact and spiritual union. Taken in this sense, death is a mere illusion which appears to those who cannot grasp the one absolute reality.
There are other passages in which this absolute reality is regarded as on, which is undetermined in itself, but from which all our faculties and experiences emanate in concrete determinations. We have thus in ourselves an epitome of the emergence of the world from Brahman. From the subtle state of indifference in deep dreamless sleep one suddenly awakes to the varied experiences of ordinary life.
Similarly, concrete varieties of objects have emerged into being from the pure subtle being of Brahman, in which they existed in an undivided and undifferentiated state. Since that which emerges into manifold variety ultimately loses itself in the being of the transcendent cause, and since the transcendent cause alone remains unchanged through all the processes of emergence and dissolution, which alone is the truth. The multiplicity of things is false, for the truth in them is the one abiding essence.
The Upanishads are not philosophy, if we mean by the word philosophy a reasoned account or a rationalization of experiences; yet they contain suggestions of rationalization as to the nature of reality from concrete experience of dreamless sleep and from ineffable mystical experience. Though ineffable, the mystical experience is not regarded as an ecstatic communion with the divine; it is a revelation of the subtlest essence of our being, which lies far below the depth of the common animal man.
It is only when we transcend the limits of the ordinary biological man that we can come in contact with the pure personality which the Upanishads call the Atman or the self. This pure self is one in all and is identical with the highest reality of the universe.
It is pure spirituality and pure experience (Jnana) and, as such, the absolute concrete truth which is imminent and transcendent at the same time in all our experiences and in all objects denoted by it. It is infinite reality, limitless and illimitable.
The Upanishads thus lay the foundation of all later Hindu philosophy. All Hindu thinkers accept in more or less modified form the fundamental tenet of the Upanishads that self is the ultimate reality, and all experiences are extraneous to it.
By the beginning of the Christian era six philosophical schools or systems had emerged in Hinduism. Though differing vary widely, they were all looked on as orthodox, since they all accepted the inspiration of the Vedas and the claim of the brahmans to’ ritual supremacy.