The Praçna Upanishad, written in prose and apparently belonging to the Pippalada recension of the Atharva-veda, is so called because it treats, in the form of questions (praçna) addressed by six students of Brahma to the sage Pippalada, six main points of the Vedanta doctrine. These questions concern the origin of matter and life (prana) from Prajapati; the superiority of life (prana) above the other vital powers; the nature and divisions of the vital powers; dreaming and dreamless sleep; meditation on the syllable om; and the sixteen parts of man. The Mandukya is a very short prose Upanishad, which would hardly fill two pages of the present book. Though bearing the name of a half-forgotten school of the Rigveda, it is reckoned among the Upanishads of the Atharva-veda. It must date from a considerably later time than the prose Upanishads of the three older Vedas, with the unmethodical treatment and prolixity of which its precision and conciseness are in marked contrast. It has many points of contact with the Maitrayana Upanishad, to which it seems to be posterior. It appears, however, to be older than the rest of the treatises which form the fourth class of the Upanishads of the Atharva-veda. Thus it distinguishes only three morae in the syllable om, and not yet three and a half. The fundamental idea of this Upanishad is that the sacred syllable is an expression of the universe. It is somewhat remarkable that this work is not quoted by Çankara; nevertheless, it not only exercised a great influence on several Upanishads of the Atharva-veda, but was used more than any other Upanishad by the author of the well-known later epitome of the Vedanta doctrine, the Vedanta-sara. It is, however, chiefly important as having given rise to one of the most remarkable products of Indian philosophy, the Karika of Gaudapada. This work consists of more than 200 stanzas divided into four parts, the first of which includes the Mandukya Upanishad. The esteem in which the Karika was held is indicated by the fact that its parts are reckoned as four Upanishads. There is much probability in the assumption that its author is identical with Gaudapada, the teacher of Govinda, whose pupil was the great Vedantist commentator, Çankara (800 A.D.). The point of view of the latter is the same essentially as that of the author of the Karika, and many of the thoughts and figures which begin to appear in the earlier work are in common use in Çankara's commentaries. Çankara may, in fact, be said to have reduced the doctrines of Gaudapada to a system, as did Plato those of Parmenides. Indeed, the two leading ideas which pervade the Indian poem, viz., that there is no duality (advaita) and no becoming (ajati), are, as Professor Deussen points out, identical with those of the Greek philosopher.