In language the Brahmanas are considerably more limited in the use of forms than the Rigveda. The subjunctive is, however, still employed, as well as a good many of the old infinitives. Their syntax, indeed, represents the oldest Indian stage even better than the Rigveda, chiefly of course owing to the restrictions imposed by metre on the style of the latter. The Brahmanas contain some metrical pieces (gathas), which differ from the prose in which they are imbedded by certain peculiarities of their own and by a more archaic character. Allied to these is a remarkable poem of this period, the Suparnadhyaya, an attempt, after the age of living Vedic poetry had come to an end, to compose in the style of the Vedic hymns. It contains many Vedic forms, and is accented, but it betrays its true character not only by its many modern forms, but by numerous monstrosities due to unsuccessful imitation of the Vedic language. A further development are the Aranyakas or "Forest Treatises," the later age of which is indicated both by the position they occupy at the end of the Brahmanas and by their theosophical character. These works are generally represented as meant for the use of pious men who have retired to the forest and no longer perform sacrifices. According to the view of Professor Oldenberg, they are, however, rather treatises which, owing to the superior mystic sanctity of their contents, were intended to be communicated to the pupil by his teacher in the solitude of the forest instead of in the village. In tone and content the Aranyakas form a transition to the Upanishads, which are either imbedded in them, or more usually form their concluding portion. The word upa-ni-shad (literally "sitting down beside") having first doubtless meant "confidential session," came to signify "secret or esoteric doctrine," because these works were taught to select pupils (probably towards the end of their apprenticeship) in lectures from which the wider circle was excluded. Being entirely devoted to theological and philosophical speculations on the nature of things, the Upanishads mark the last stage of development in the Brahmana literature. As they generally come at the end of the Brahmanas, they are also called Vedanta ("end of the Veda"), a term later interpreted to mean "final goal of the Veda." "Revelation" (çruti) was regarded as including them, while the Sutras belonged to the sphere of tradition (smriti). The subject-matter of all the old Upanishads is essentially the same--the doctrine of the nature of the Atman or Brahma (the supreme soul). This fundamental theme was expounded in various ways by the different Vedic schools, of which the Upanishads were originally the dogmatic text-books, just as the Brahmanas were their ritual text-books.