The philosophy of ancient India is quite diverse and complex in structure. So complex, in fact, that many, Indians included, give up on making sense of this kaleidoscope. This article is a humble attempt to present a streamlined simplification of this complicated set of ideas and concepts.
The word "Vedanta" literally means "end of the Veda" in Sanskrit. In common use, however, the word is used with reference to the concluding portions of the Vedic literature, known also as the Upanishads. While the Vedas were composed between 3500 B.C. and 500 B.C., the Upanishads began to come together towards the end of this period, which coincided with the lives of Buddha and Mahavira, the founders of Buddhism and Jainism. Thus, all these three share common traits.
Though not the only authority, the Upanishads are beyond question the highest authority as far as the Vedanta and the schools which claim this name are concerned. The name Vedanta is applied to all the five systems of philosophy, going under the names of Samkara, Ramanuja, Nimbarka, Madhva and Vallabha, because all these five systems alike lay claim to their being specially and directly derived from the Vedanta. Really speaking, the other five orthodox schools are also said to derive their support from the Upanishads.
For example, the Nyaya and Vaisesika schools quote passages from the Upanishads in support of their particular reasoning, especially when they are treating of the nature and attributes of the soul, or of the difference of nature between Ishwara, the unpersonified divine and the inanimate world. Above all, the Samkhyas, a very old and influential school, whose general influence is clearly seen throughout the philosophical literature of India, are seen to make a very great use of passages from the Upanishads, though it must be pointed out that even according to themselves, their main-stay is not the Upanishads, but reasoning pure and simple.
The greatest insights into life and the human being can be found in this vast canon of literature. However, the very vastness of the work can sometimes lead to confusion. One can often find contradictory statements in two different books, and sometimes in the same book itself. Thus for instance, in one place it is said that there was existence in the beginning. In another place it is said that there was non-existence in the beginning. In one place it is said that all is intelligence, which is one and unique. In another place, on the other hand, there is a reference to two persons, one of whom eats and the other only looks on. Apart from this, the nature of the Sanskrit language -- in which these texts are written -- also lends itself to various interpretations. One and the same passage can be interpreted in several ways.
However, in many instances, this seeming contradiction is intentional. This is especially so in the Vedanta, the most refined of the Indian subcontinent's philosophical traditions. The sages who put this canon together, for the most part realized that pure logic alone cannot take one to an understanding of creation, which is quite illogical in nature. They were quite clear that "illogical" is not the same as "unsystematic". A deep sense of harmony and system underlay the organization of the universe, they said. However, this underlying sense of order could not be grasped by the mind, which was geared towards what is necessary for the survival of humanity, not for the pursuit of understanding the roots of creation. We see scientists making similar statements today, when they say that the human mind cannot understand quantum mechanics or relativity, except by playing with equations.
This truth was known to the sages of ancient India, and thus, they used the logical treatises of the Vedanta as a tool to take one to a point of refined logic, beyond which the reader could enter the realm of illogic. One method used for this was to take contradictory paths of reasoning and reach the same conclusion, thus placing the whole of one's logic on shaky ground.