while Badarayana's Brahma Sūtras focused on internalized philosophy as the spiritual path. The text reviews and critiques most major orthodox schools of Hindu philosophy as well as all heterodox Indian philosophies such as Buddhism, with the exception of Samkhya and Yoga philosophies which it holds in high regards and recurrently refers to them in all its four chapters, adding in sutras 2.1.3 and 4.2.21 that Yoga and Samkhya are similar. The text cites and quotes from the ten Principal Upanishads often, the Kaushitaki Upanishad and the Shvetashvatara Upanishad in several sutras, but also mentions Upanishads now unknown and lost. The contents of the text also acknowledge and analyze the various Vedic schools, and mentions the existence of multiple, diverging versions of the same underlying text. The sutras of the Brahma Sūtras are aphorisms, which Paul Deussen states to be "threads stretched out in weaving to form the basis of the web", and intelligible "when the woof is added" with a commentary. Chapter 1: What is Brahman? The first chapter is regarded in Vedanta tradition as Samanvaya (Harmony), because it distills, synchronizes and brings into a harmonious whole the seemingly diverse and conflicting passages in various Sruti texts. It consists of 134 sutras, with eleven Adhikaranas in the first Pada, seven Adhikaranas in second, fourteen Adhikaranas in third, and eight in the fourth Pada. The different sub-schools of Vedanta have interpreted the sutras in the last Pada differently, and some count only seven Adhikaranas in the fourth Pada. This Brahma Sūtras chapter asserts that all the Upanishads primarily aim and coherently describe the knowledge and meditation of Brahman, the ultimate reality. Brahman is the source from which the world came into existence, in whom it inheres and to which it returns. The only source for the knowledge of this Brahman is the Sruti or the Upanishads. The sutras 1.1.5-11 quotes the Samkhya school's view that the Principle of the world is unconscious, and instead asserts that the Principle of the world is conscious and the Brahman itself. The remaining sutras in Pada 1.1, all sutras of 1.2 and 1.3 assert that Brahman is the primary focus of the Upanishads, is various aspects of empirical reality, quoting various verses in support, from Taittiriya Upanishad, Chandogya Upanishad, Kaushitaki Upanishad, Mundaka Upanishad, Katha Upanishad, Brihadaranyaka Upanishad and Prashna Upanishad. The first chapter in sutras 1.4.1-15 presents the Samkhya theories on Prakriti, and presents its