These together with the “Maitrayaniya” or “Maitri” Upanishad constitute the principal Upanishads. Ramanuja uses all these Upanishads as also the “Subala” and the “Culika”. He mentions als the “Garbha”, the “Jabala” and the “Maha” Upanishads. Vidyaranya includes “Nrsimhottara-tapani” Upanishad among the twelve he explained in his “Sarvopanishad-arthanubhuti-prakasa.” The other Upanishads which have come down are more religious than philosophical. They belong more to the Purana and the Tantra than to the Veda. They glorify Vedanta or Yoga or Samnyasa or extol the worship of Shiva, Shakti or Vishnu.
Modern criticism is generally agreed that the ancient prose Upanishads; Aitareya, Kausitaki, Chhandogya, Kena, Taittiriya and Brhadaranyaka, together with Isa and Katha belong to the eighth and seventh centuries B. C. They are all pre Buddhistic. They represent the Vedanta in its pure original form and are the earliest philosophical compositions of the world. These Upanishads belong to what Karl Jaspers calls he Axial Era of the world, 800 to 300 B.C, when man for the first time simultaneously and independently in Greece, China and India questioned the traditional pattern of Life.
As almost all the early literature of India was anonymous, we do not know the names of the authors of the Upanishads. Some of the chief doctrines of the Upanishads are associated with the names of renowned sages as Aruni, Yajnavalkya, Balaki, Svetaketu, Sandilya. They were, perhaps, the early exponents of the doctrines attributed to them. The teachings were developed in Uparishads or spiritual retreats where teachers and pupils discussed and defined the different views.
As a part of the Veda, The Upanishads Belong to Shruti or revealed literature. They are immemorial, Santana, timeless. Their truths are said to be breathed out by God or visioned by the seers. They are the utterances of the sages who speak out of the fullness of their illumined experience. They are not reached by ordinary perception, inference or reflection, but “seen” by the seers, even as we see and not infer the wealth and riot of color in the summer sky.
The seers have the same sense of assurance and possession of their spiritual vision as we have of our physical perception. The sages are men of “direct” vision, in the words of Yaska, “Sakshat-krta-dharamana”, and the records of their experiences are the facts to be considered by any philosophy of religion. The truths revealed to the seers are not mere reports of introspection which are purely subjective. The inspired sages proclaim that the knowledge they communicate is not what they discover for themselves.
It is revealed to them without their effort. Though the knowledge is an experience of the seer, it is an experience of an independent reality which impinges on his consciousness. There is the impact of the real on the spirit of the experiencer. It is therefore said to be a direct disclosure from the ‘wholly other’. A revelation of the divine.
Symbolically, the Upanishads describe revelation as the breath of god blowing on us. Of that great being, this is the breath, which is the “Rig Veda”. The divine energy is compared to the breath which quickens. It is a seed which fertilizes or a flame which kindles the human spirit to its finest issues. It is interesting to know that the Brhadaranyaka Upanishad tells us that not only the Vedas but history, sciences and other studies are also “breathed forth by the great God’.
The Vedas were composed by the seers when they were in a state of inspiration. He who inspires them is a God. Truth is impersonal, “apaurushaiya” and eternal, “nitya”. Inspiration is a joint activity of which man’s contemplation and God’s revelation are two sides. The Svetasvatara Upanishad says that the sage Svetasvatra saw the truth owing to his power of contemplation “tapah- prabhava” and the grace of god, “deva-prasada”. The dual significance of revelation, its subjective and objective character, is suggested here.
The Upanishads are vehicles more of spiritual illumination than of systematic reflection. They reveal to us a world of rich and varied spiritual experience rather than a world of abstract philosophical categories. Their truths are verified not only by logical reason, but by personal experience. Their aim is practical rather than speculative. Knowledge is a means to freedom. Philosophy, “Brahma-vidya” is the pursuit of wisdom by a way of life.