Brahma Sutras / Vedanta Sutras of Badarayana.
The Brahma sūtras, also called Vedanta Sūtras, constitute the Nyāya prasthāna, the logical starting point of the Vedānta philosophy (Nyāya = logic/order). No study of Vedānta is considered complete without a close examination of the Prasthāna Traya, the texts that stand as the three starting points.
While the Upanishads (Śruti prasthāna, the starting point of revelation) and the Bhagavad-Gītā (Smriti prasthāna, the starting point of remembered tradition) are the authoritative Vedānta source texts, it is in the Brahma sūtras that the teachings of Vedānta are set forth in a systematic and logical order. The Brahma Sūtras reconcile seemingly contradictory teachings of the various Upanishads, by placing each text in a doctrinal context. The word sūtra means thread, and the Brahma sūtras literally stitch together the various teachings of the Upanishads and the Gītā into a logical and self-consistent whole. However, the Brahma Sūtras are themselves so terse that they are often incomprehensible without the aid of the various commentaries handed down in the main schools of Vedānta thought. The Brahma Sūtras are also known by other names: Vedānta Sūtras, Uttara Mimāmsā-sūtras, Śāriraka Sūtras, Śāriraka Mimāmsā-sūtras and the Bhikshu sūtras.
The Vedānta Sūtras themselves supply ample evidence that at a very early time, i.e. a period before their own final composition, there were differences of opinion among the various interpreters of the Vedānta. Quoted in the Vedānta Sūtras are opinions ascribed to Audulomi, Kārshnāgni, Kāśakŗtsna, Jaimini and Bādari, in addition to Bādarāyaņa.
The Brahma Sūtras consist of 555 aphorisms or sūtras, in 4 chapters (adhyāya), each chapter being divided into 4 quarters (pāda). Each quarter consists of several groups of sūtras called Adhikaraņas or topical sections. An Adhikaraņa usually consists of several sūtras, but some have only one sūtra. The first chapter (Samanvaya: harmony) explains that all the Vedānta texts talk of Brahman, the ultimate reality, which is the goal of life. The second chapter (Avirodha: non-conflict) discusses and refutes the possible objections against Vedānta philosophy. The third chapter (Sādhana: the means) describes the process by which ultimate emancipation can be achieved. The fourth chapter (Phala: the fruit) talks of the state that is achieved in final emancipation.