Before entering into the philosophy of the Upani@sads it may be worth while to say a few words as to the reason why diverse and even contradictory explanations as to the real import of the Upani@sads had been offered by the great Indian scholars of past times. The Upani@sads, as we have seen, formed the concluding portion of the revealed Vedic literature, and were thus called the Vedanta. It was almost universally believed by the Hindus that the highest truths could only be found in the revelation of the Vedas. Reason was regarded generally as occupying a comparatively subservient place, and its proper use was to be found in its judicious employment in getting out the real meaning of the apparently conflicting ideas of the Vedas. The highest knowledge of ultimate truth and reality was thus regarded as having been once for all declared in the Upani@sads. Reason had only to unravel it in the light of experience. It is important that readers of Hindu philosophy should bear in mind the contrast that it presents to the ruling idea of the modern world that new truths are discovered by reason and experience every day, and even in those cases where the old truths remain, they change their hue and character every day, and that in matters of ultimate truths no finality can ever be achieved; we are to be content only with as much as comes before the purview of our reason and experience at the time. It was therefore thought to be extremely audacious that any person howsoever learned and brilliant he might be should have any right to say anything regarding the highest truths simply on the authority of his own opinion or the reasons that he might offer. In order to make himself heard it was necessary for him to show from the texts of the Upani@sads that they supported him, and that their purport was also the same. Thus it was that most schools of Hindu philosophy found it one of their principal duties to interpret the Upani@sads in order to show that they alone represented the true Vedanta doctrines. Any one who should feel himself persuaded by the interpretations of any particular school might say that in following that school he was following the Vedanta.
The difficulty of assuring oneself that any interpretation is absolutely the right one is enhanced by the fact that germs of diverse kinds of thoughts are found scattered over the Upani@sads which are not worked out in a systematic manner. Thus each interpreter in his turn made the texts favourable to his own doctrines prominent and brought them to the forefront, and tried to repress others or explain them away. But comparing the various systems of Upani@sad interpretation we find that the interpretation offered by S'a@nkara very largely represents the view of the general body of the earlier Upani@sad doctrines, though there are some which distinctly foreshadow the doctrines of other systems, but in a crude and germinal form. It is thus that Vedanta is generally associated with the interpretation of S'a@nkara and S'a@nkara's system of thought is called the Vedanta system, though there are many other systems which put forth their claim as representing the true Vedanta doctrines.
Under these circumstances it is necessary that a modern interpreter of the Upani@sads should turn a deaf ear to the absolute claims of these exponents, and look upon the Upani@sads not as a systematic treatise but as a repository of diverse currents of thought--the melting pot in which all later philosophic ideas were still in a state of fusion, though the monistic doctrine of S'a@nkara, or rather an approach thereto, may be regarded as the purport of by far the largest majority of the texts. It will be better that a modern interpreter should not agree to the claims of the ancients that all the Upani@sads represent a connected system, but take the texts independently and separately and determine their meanings, though keeping an attentive eye on the context in which they appear. It is in this way alone that we can detect the germs of the thoughts of other Indian systems in the Upani@sads, and thus find in them the earliest records of those tendencies of thoughts.