“The Bhagavadgīta which is called an Upanısad, also the Smrti, par excellence, and the Śvetāśvatara Upanisad are works of Vedānta, but show clear traces of the influence of the Āgamas. Garbe has pointed out the influence of the Bhāgavata(Vaisnava) Āgamas on the former The latter bears equally clear traces of the influence of the Śaiva cult. Both works seem to be due to an ancient synthesizing movement in which was attempted a higher standpoint than the monism of the Upanisads, the pluralism of the Sānkhya and the Vaiśesika and the three tattvas (triple reality) of the Āgama schools, a standpoint from which all three can be reconciled and treated as different aspects of the higher point of view."
The Āgamas in general claim to be based on the Nigama or Veda There is also the view that both are derived from a common root or Mūla Veda Hārīta, for example, states in his Dharma Śāstra that Śruti is of two kinds— the Vedic and Tantric (or Āgamic) (श्रुतिप्रमाणको धर्म.। श्रुतिश्च द्विविधा । वैदिकी तान्त्रिकी चेति ।). In later times, however, there seems to have arisen a school which held that the Āgama was inferior to, and less authoritative than the Nigama and that the Āgama path was only for those who were not equal to treading the Vedāntic path It is to refute this view that, about ten centuries ago, Śrī Yāmunācārya, the father of the Vaisnava Viśistādvaita school of Śrī Rāmānuja, seems to have found it necessary to write his famous work, the Āgama prāmānya, for upholding the view that Āgama is as equally authoritative as the Nigama or Veda - a view acceptable to all the three great Ācāryas- Śri Sankara, Śrī Rāmānuja and Śrī Madhva--so far as we may infer such a view from the fact that all of them were the greatest Vedāntins as well as most devout followers of the Āgama path It is this fact that has been referred to in the following statement of the late P T Srinivasa Iyengar.
