But in the long run two causes must have acted with ever-increasing force, to give an impulse to the systematic working up of the teaching of the Upanishads also. The followers of the different Vedic sakhas no doubt recognised already at an early period the truth that, while conflicting statements regarding the details of a sacrifice can be got over by the assumption of a vikalpa, i.e. an optional proceeding, it is not so with regard to such topics as the nature of Brahman, the relation to it of the human soul, the origin of the physical universe, and the like. Concerning them, one opinion only can be the true one, and it therefore becomes absolutely incumbent on those, who look on the whole body of the Upanishads as revealed truth, to demonstrate that their teaching forms a consistent whole free from all contradictions. In addition there supervened the external motive that, while the karmaka/nd/a of the Veda concerned only the higher castes of brahmanically constituted society, on which it enjoins certain sacrificial performances connected with certain rewards, the j/n/anaka/nd/a, as propounding a certain theory of the world, towards which any reflecting person inside or outside the pale of the orthodox community could not but take up a definite position, must soon have become the object of criticism on the part of those who held different views on religious and philosophic things, and hence stood in need of systematic defence. At present there exists a vast literature connected with the two branches of the Mima/m/sa. We have, on the one hand, all those works which constitute the Purva Mima/m/sa-/s/astra--or as it is often, shortly but not accurately, termed, the Mima/m/sa-/s/astra--and, on the other hand, all those works which are commonly comprised under the name Vedanta-/s/astra. At the head of this extensive literature there stand two collections of Sutras (i.e. short aphorisms constituting in their totality a complete body of doctrine upon some subject), whose reputed authors are Jainini and Badaraya/n/a. There can, however, be no doubt that the composition of those two collections of Sutras was preceded by a long series of preparatory literary efforts of which they merely represent the highly condensed outcome. This is rendered probable by the analogy of other /s/astras, as well as by the exhaustive thoroughness with which the Sutras perform their task of systematizing the teaching of the Veda, and is further proved by the frequent references which the Sutras make to the views of earlier teachers. If we consider merely the preserved monuments of Indian literature, the Sutras (of the two Mima/m/sas as well as of other /s/astras) mark the beginning; if we, however, take into account what once existed, although it is at present irretrievably lost, we observe that they occupy a strictly central position, summarising, on the one hand, a series of early literary essays extending over many generations, and forming, on the other hand,