It is hardly possible to attempt a history of Indian philosophy in the manner in which the histories of European philosophy have been written. In Europe from the earliest times, thinkers came one after another and offered their independent speculations on philosophy. The work of a modern historian consists in chronologically arranging these views and in commenting upon the influence of one school upon another or upon the general change from time to time in the tides and currents of philosophy. Here in India, however, the principal systems of philosophy had their beginning in times of which we have but scanty record, and it is hardly possible to say correctly at what time they began, or to compute the influence that led to the foundation of so many divergent systems at so early a period, for in all probability these were formulated just after the earliest Upani@sads had been composed or arranged.
The systematic treatises were written in short and pregnant half-sentences (_sutras_) which did not elaborate the subject in detail, but served only to hold before the reader the lost threads of memory of elaborate disquisitions with which he was already thoroughly acquainted. It seems, therefore, that these pithy half-sentences were like lecture hints, intended for those who had had direct elaborate oral instructions on the subject. It is indeed difficult to guess from the sutras the extent of their significance, or how far the discussions which they gave rise to in later days were originally intended by them. The sutras of the Vedanta system, known as the S'ariraka-sutras or Brahma-sutras of Badaraya@na for example were of so ambiguous a nature that they gave rise to more than half a dozen divergent interpretations, each one of which claimed to be the only faithful one. Such was the high esteem and respect in which these writers of the sutras were held by later writers that whenever they had any new speculations to offer, these were reconciled with the doctrines of one or other of the existing systems, and put down as faithful interpretations of the system in the form of commentaries. Such was the hold of these systems upon scholars that all the orthodox teachers since the foundation of the systems of philosophy belonged to one or other of these schools. Their pupils were thus naturally brought up in accordance with the views of their teachers. All the independence of their thinking was limited and enchained by the faith of the school to which they were attached. Instead of producing a succession of free-lance thinkers having their own systems to propound and establish, India had brought forth schools of pupils who carried the traditionary views of particular systems from generation to generation, who explained and expounded them, and defended them against the attacks of other rival schools which they constantly attacked in order to establish the superiority of the system to which they adhered. To take an example, the Nyaya system of philosophy consisting of a number of half-sentences or sutras is attributed to Gautama, also called Ak@sapada. The earliest commentary on these sutras, called the _Vatsyayana bha@sya_, was written by Vatsyayana. This work was sharply criticized by the Buddhist Di@nnaga, and to answer these criticisms Udyotakara wrote a commentary on this commentary called the _Bha@syavattika_ [Footnote ref 90]. As time went on the original force of this work was lost, and it failed to maintain the old dignity of the school. At this Vacaspati Mis'ra wrote a commentary called _Varttika-tatparya@tika_ on this second commentary, where he tried to refute all objections against the Nyaya system made by other rival schools and particularly by the Buddhists. This commentary, called _Nyaya-tatparya@tika_, had another commentary called _Nyaya-tatparya@tika-paris'uddhi_ written by the great Udayana. This commentary had another commentary called _Nyaya-nibandha-prakas'a_ written by Varddhamana the son of the illustrious Ga@nges'a. This again had another commentary called _Varddha-manendu_ upon it by Padmanabha Mis'ra, and this again had another named _Nyaya-tatparyama@n@dana_ by S'a@nkara Mis'ra. The names of Vatsyayana, Vacaspati, and Udayana are indeed very great, but even they contented themselves by writing commentaries on commentaries, and did not try to formulate anyoriginal system. Even S'a@nkara, probably the greatest man of India after Buddha, spent his life in writing commentaries on the _Brahma-sutras_, the Upani@sads, and the _Bhagavadgita_.
As a system passed on it had to meet unexpected opponents and troublesome criticisms for which it was not in the least prepared. Its adherents had therefore to use all their ingenuity and subtlety in support of their own positions, and to discover the defects of the rival schools that attacked them. A system as it was originally formulated in the sutras had probably but few problems to solve, but as it fought its way in the teeth of opposition of other schools, it had to offer consistent opinions on other problems in which the original views were more or less involved but to which no attention had been given before.
The contributions of the successive commentators served to make each system more and more complete in all its parts, and stronger and stronger to enable it to hold its own successfully against the opposition and attacks of the rival schools. A system in the sutras is weak and shapeless as a newborn babe, but if we take it along with its developments down to the beginning of the seventeenth century it appears as a fully developed man strong and harmonious in all its limbs. It is therefore not possible to write any history of successive philosophies of India, but it is necessity that each system should be studied and interpreted in all the growth it has acquired through the successive ages of history from its conflicts with the rival systems as one whole [Footnote ref 91]. In the history of Indian philosophy we have no place for systems which had their importance only so long as they lived and were then forgotten or remembered only as targets of criticism. Each system grew and developed by the untiring energy of its adherents through all the successive ages of history, and a history of this growth is a history of its conflicts. No study of any Indian system is therefore adequate unless it is taken throughout all the growth it attained by the work of its champions, the commentators whose selfless toil for it had kept it living through the ages of history.