Hindu tantra is a post-Vedic phenomena whose seed forms can be located in Vedic, Brahmanic, and even ancient autochthonous sources. However, while we can located certain strain and ideas pre-existing what he would term Tantric schools, it was not until much later that we see these schools developing.
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Padoux is quick to point out that Tantra is functionally sectarian.That is, there is no coherent or concrete doctrine of theory or practice that can be consulted, decoded and re-presented in Western academic terms, but rather an amalgamation of many divergent, often conflicting and competing, sectarian groups.
He chooses to delineate these groups based upon traditional ideas of sectarian division: Shaivite, Vaishnaivite, and Shakta, while simultaneously acknowledging the difficulty in distinguishing these three streams in some lineages.
"The main division of Sects is made between worshipers of Vishnu (Vaishnavas), of Shiva (Shaivas) and of the Goddess (Shaktas), the last two being sometimes difficult to distinguish clearly, if only because Shiva and Shakti are metaphysically inseparable and therefore necessarily conceived, even in temples, in some relationship."
These sectarian division are even further subdivided into schools or guru lineages, some of which include Trika (padoux's favorite) Spanda, Kula, and Kapalika etc., though Padoux is hesitant to delineate the
differences between them.