Re Shakti and tantra :- the "goddess power" and "spiritual weaving/ continuity" : A Buddhist perspective
Re Austin ( tribe: dark goddesses ):
". . .Now, I'm someone who doesn't even believe in any real difference between Vedic and Tantric religion, so is it just a "tribal" religion completely unrelated to Vedic or Tantric traditions to you? Or a foreign influence of some kind? I don't get it."
In Buddhist Sanskrit, Tantra has several essential meanings. One is "weaving" or "continuity", as in the integrity or interconnectedness of a yoga method. Related to this is the integrity or interconnectedness of the subtle components ( psychophysical aggregates ) of the human energy system. A deeper meaning is "primordial being" in the specifically Buddhist sense of Dharmakaya, as explicitly taught and practiced in the transmissions of the Great Perfection ( Atiyoga ) and Great Seal ( Mahamudra ).
In practical terms, the basic idea of Buddhist scripture and yoga is this: all beings are inherently pure of limitations and obscurations because all beings are natively one with dharmakaya / primordial purity. This is the foundational meaning or basis of Buddhatantra, Atiyoga and Mahamudra. It has nothing to do with a creator god or externalist kind of shakti religion.
There are quite a few translations of classical scriptures on "dharmakaya/ primordial being" and the Buddhist usages of the term "tantra". Of these, one of the most important is the Uttaratantra, the "Sublime Continuity of the Great Way" Explanatory Scripture. See
"Buddha Nature: The Mahayana Uttaratantra Shastra with Commentary by Arya Maitreya (Author)",
Publisher: Snow Lion Publications ( 2000 )
# ISBN-10: 1559391286
"Enhanced with exceptional and informative commentary by Jamgon Kongtrul Lodro Thaye, and with additional explanations by Khenpo Tsultrim Gyamtso Rinpoche, Buddha Nature is one of the finest, most accessible presentations on the basis and process of enlightenment within Buddhism. A seminal, benchmark publication, no dedicated student of Buddhist enlightenment can omit a careful and reflective reading of Buddha Nature."
This is for Great Way Buddhists a quintessential key to understanding the theory and practice of tantra, Buddha nature and the meaning of realization on the stages of the path ( bodhisattva-bhumi ). It is classical tantra which is not tribal and which is not Hindu, Bonpo, and so forth. So that definitively answers your question.
Having said this, I will turn now to the broader multicultural area which includes both Buddhist and non-Buddhist tantra. In summary, there are diverse streams of tantra, Austin, and these are sometimes interwoven. Examples follow.
1) Sanatana Dharma ( "Hinduism" ) has Shakti cult and devi yoga ( goddess practices ) and tantra woven in.
2) Buddhatantra has shakti cult and devi yoga and tantra woven in.
3) Bon ( pre-Buddhist ) central Asian mysticism has shakti cult and devi yoga and tantra woven in.
4) The 3H0 Sikhs begin their kundalini yoga practice sessions with the evocation "Adi shakti, Adi Shakti namo namo." And some of their sadhanas are claimed to go way way back, to very ancient times. This could be true of their "MAAAA" recitation / asana. The basic point in this respect is that the kundalini yoga parampara, which is a primary and classical shakti cycle of teachings, is very ancient and multiply sourced. This is definitely stated in several of the Kundalini Research Institute publications.
5) Jain dharma has some tantra woven in, but I know little or nothing about it other than historical attestation through their temple imagery.
Therefore it is clear that shakti type practice must be agreed to be trans-religious according to source Indian traditions. It is also clear that there is definite sharing of some of the yogas ( such as Devi mantras and Shiva yogas ) between Hindus and Buddhists, between Hindus and Bonpo, between Buddhists and Bonpos, and more generalized quasi-traditions.
Also we should keep in mind that the Buddhist traditions of internal energy yoga, pranayama and bandha, and devi yoga are INDEPENDENT of the Hindu sources and traditions. The Buddhist teachings and yogas are self-standing and do not depend directly or primarily or even in major usages upon the Hindu theory, practice or culture.
A key example of this is the Buddhist set of teachings known as the Great Perfection, or Atiyoga. This is a vast and powerful set of teachings and yogas which does not in any way derive ( in the Buddhist lineage ) from any Hindu teacher or lineage, nor any Bonpo teacher or lineage.
The Great Perfection / Atiyoga incorporates many fairly standard usages as found in Hindu and Buddhist ritual and tantra, including devi yoga. However, the Great Perfection is not based on shakti per se. The Great Perfection is based on the Breakthrough Precepts of Primordial Purity and Spontaneous Presence, in which appearance and liberating wisdom are co-arising. In Buddhist Sanskrit, the key technical term would be translated as "Primordial And Pervasive", not the same thing as shakti or kundalini yoga or devi worship as in the non-Buddhist schools.
The central deity of this transmission-lineage is Vajrasattva / Vajragarvi: this is the primary deity yoga which is transmitted in the Breakthrough ( dzogchen trekcho ) cycle. This is also the root deity from which manifested Joyous Vajra, the original human teacher of ( Buddhist ) Great Perfection ( in this historical time cycle ). Vajrasattva is not a Hindu deity, and the Bonpo do not use the Hundred Syllable Vajrasattva mantra.
It is a common mistake of Buddhists, Hindus, Bonpos and western "scholars" to think ( i.e. expect ) that Buddhist tantra, Buddhist gods and goddesses, Buddhist practices of internal energy yoga, Buddhist mantras and so forth derive mainly or substantially from non-Buddhist sources.
A key example is that of the Goddess Tara. Yes, Tara is both a Hindu and Buddhist goddess. But the Buddhist scriptures and mantras and deity yogas for Tara do not derive from specifically Hindu sources ( although they definitely overlap in secondary respects ). The Hindu tantras and mantras for Tara have distinctively different archetypes and scriptures.
These are not related to the Buddhist scripture, the "Arya Tare Mantra Mula Stottra Nama Skeri Kawing Shatika Nama" and so forth. This is a fairly common misunderstanding. In fact, there may well be more Buddhist Tara practice in Hinduism than there is Hindu Tara practice in Buddhism.
There are significant areas of overlap between Buddhist tantra and non Buddhist tantra. However, the fundamental principles models and practices of Buddhist soteriology, Buddhist scripture, Buddhist yoga and so forth would work the same whether the non-Buddhist traditions such as the Shiva yogas and Bon cho had ever existed or not. This is true from the basic cycles of teaching on pratimokshayana, the bodhisattvayana, the Buddhatantra, up through and including the quintessential doctrines of Great Perfection / Atiyoga and Great Seal / Mahamudra.
Having given a basic overall view of this topic, I will now recommend two important discussion texts, on Hindu goddess yoga and on Buddhist Great Perfection. Both are by major, recognized gurus.
"Tantric Yoga and the Wisdom Goddesses (Paperback)"
by David Frawley
"The Crystal and the Way of Light (Paperback)"
by Namkhai Norbu (Author), John Shane (Editor)
Together these three texts convey a great deal about tantra, both Hindu and Buddhist, and about the inner mystical approach to yoga. To actually practice tantra requires, classically speaking, a living lineage connection, a set of tantric vows, and a set of yoga practices. These must be integrated into one's sadhana and one's life to become real and effective.
Thus tantra is not based on philosophy and dogma in the religious or intellectual senses of these terms, tantra is based on the transmission and practice of an esoteric yoga in which the person is already divine by nature, and seeks to integrate all aspects of life with a formal internal discipline of awareness and subtle energy which manifests divinity.