We have now arrived at the third and last stage of Vedic literature, that of the Sutras. These are compendious treatises dealing with Vedic ritual on the one hand, and with customary law on the other. The rise of this class of writings was due to the need of reducing the vast and growing mass of details in ritual and custom, preserved in the Brahmanas and in floating tradition, to a systematic shape, and of compressing them within a compass which did not impose too great a burden on the memory, the vehicle of all teaching and learning. The main object of the Sutras is, therefore, to supply a short survey of the sum of these scattered details. They are not concerned with the interpretation of ceremonial or custom, but aim at giving a plain and methodical account of the whole course of the rites or practices with which they deal. For this purpose the utmost brevity was needed, a requirement which was certainly met in a manner unparalleled elsewhere. The very name of this class of literature, sutra, "thread" or "clue" (from siv, "to sew"), points to its main characteristic and chief object--extreme conciseness. The prose in which these works are composed is so compressed that the wording of the most laconic telegram would often appear diffuse compared with it. Some of the Sutras attain to an almost algebraic mode of expression, the formulas of which cannot be understood without the help of detailed commentaries. A characteristic aphorism has been preserved, which illustrates this straining after brevity. According to it, the composers of grammatical Sutras delight as much in the saving of a short vowel as in the birth of a son. The full force of this remark can only be understood when it is remembered that a Brahman is deemed incapable of gaining heaven without a son to perform his funeral rites. Though the works comprised in each class of Sutras are essentially the same in character, it is natural to suppose that their composition extended over some length of time, and that those which are more concise and precise in their wording are the more recent; for the evolution of their style is obviously in the direction of increased succinctness. Research, it is true, has hitherto failed to arrive at any definite result as to the date of their composition. Linguistic investigations, however, tend to show that the Sutras are closely connected in time with the grammarian Panini, some of them appearing to be considerably anterior to him. We shall, therefore, probably not go very far wrong in assigning 500 and 200 B.C. as the chronological limits within which the Sutra literature was developed.