The term prasthāna-traya (also written sthāna-traya) is of ancient Vedāntic usage and designates the three foundational 'starting-points' (prasthāna) of Indian philosophical theology. 'Prasthāna' means a point of departure or a foundation — and the term captures the idea that all Vedāntic reasoning must depart from and remain answerable to these three bodies of scripture. The three are: (1) the Upaniṣads (also called 'śruti-prasthāna' — the foundation of revealed scripture), which are the direct verbal testimony of the Vedas concerning the nature of Brahman, the individual ātman, and liberation; (2) the Brahma Sūtras of Bādarāyaṇa (also called 'nyāya-prasthāna' — the foundation of reasoning), which systematize and adjudicate the sometimes diverse teachings of the Upaniṣads through logical aphorisms; and (3) the Bhagavad Gītā (also called 'smṛti-prasthāna' — the foundation of remembered scripture), which presents the teachings of Bhagavān Śrī Kṛṣṇa to Arjuna and brings together the doctrines of jñāna, bhakti, and karma in an accessible narrative form.
In the Śrī Vaiṣṇava tradition, the prasthāna-traya holds supreme importance because Rāmānujāchārya composed his three major works as commentaries on precisely these three texts: the Śrī Bhāṣya (commentary on the Brahma Sūtras), the Gītā Bhāṣya (commentary on the Bhagavad Gītā), and the Vedārthasaṃgraha (which deals primarily with the Upaniṣadic testimony). This trio of commentaries constitutes Rāmānuja's definitive statement of Viśiṣṭādvaita Vedānta. Vedānta Deśika and subsequent ācāryas produced further commentaries on these three texts in Sanskrit and Maṇipravāḷam, deepening the sampradāya's engagement with them across centuries.
It is important to note that while the prasthāna-traya is the common foundation of all Vedāntic schools (including Advaita and Dvaita), the Śrī Vaiṣṇava tradition does not treat them in isolation from its own distinctive scriptural heritage. The Nālāyira Divya Prabandham is sometimes called the 'Tamil Veda' (Drāmiḍa Vedānta) and is treated as co-equal in authority with the Sanskrit prasthāna-traya within the Śrī Vaiṣṇava sampradāya. Nāthamunigaḷ's recovery of the Divya Prabandham and its elevation to co-canonical status is one of the defining marks of the Śrī Vaiṣṇava tradition vis-à-vis other Vedāntic schools. The sampradāya thus functions with a five-fold (or expanded triple) prasthāna: the three Sanskrit foundations plus the Divya Prabandham and the rahasyagranthams of the āchāryas.