Brahma Sutras, aphorisms about Brahma, comprise four Chapters, sixteen Sections, one hundred ninety one Topics and five hundred fifty five Sutras. The First Chapter deals with Samanvaya or Reconciliation by way of Interpretation, the Second Chapter is called Avirodha or non-contraditiction, the Third Chapter relates to Sadhana or Spiritual Practice and finally the Phala or the Accomplishment.
Chatusutri refers to the first four of the Brahma Sutras and Shankaracharya’s Bhashya on them. The introduction by Shankara to BrahmasUtra bhAShya is called upodghAtaH. This portion starting with the sentence 'yuShmadasmat....' and ending with the sentence 'yathAchaayamarthaH....pradarshayiShyAmaH' is what is popularly termed ' 'adhyAsabhAShya'. The actual bhAShya for the first four sutra-s along with this 'adhyAsabhAShya' may be collectively called the 'chatussUtrI'.
Shankara declares that all the Upanishads have this avowed purpose of eradicating the samsaara-causing ignorance,viz., adhyAsa, by bestowing the knowledge of the One Atman.
