Inner and outer vehicles
Our great teacher, Lord Buddha, gave a variety of teachings to liberate sentient beings from the sufferings of samsara. According to the Nyingma School of Tibetan Buddhism, the entire teachings given by Lord Buddha can be classified into nine vehicles. They are:
The three outer vehicles of Hearers, Solitary Realizers and Bodhisattvas are called the Vehicles that Direct the Cause of Suffering.
The three inner vehicles of Kriya (Action), Upa or Charya (Conduct) and Yoga are called the Vehicles of Vedic Asceticism.
The three secret vehicles of Mahayoga, Anuyoga and Atiyoga are called the Vehicles of Overpowering Means.
The first three vehicles belong to the sutra and the remaining six to the tantra. The tantra part is also known as Vajrayana.
Amongst the nine vehicles, the first six vehicular teachings that are common to all the Buddhist tradition initially flourished in the Central Land of Jambudvipa (India) and later they spread to the different parts of the world. Even to this day, the practitioners of the Three Main Vehicles of Shravaka, Pratyekabuddha and Bodhisattva remain and these teachings are being spread and propagated throughout the world.
The three secret vehicles of Mahayoga, Anuyoga and Atiyoga are very important teachings that reside in the One Hundred Thousand Tantras of Nyingma Tradition. These teachings are the innermost essence of all the teachings given by our teacher, Lord Buddha and they have the potential to deliver enlightenment in one life time for those who are fortunate ones. These profound, secret and esoteric teachings are called the Three Classes of Inner Tantras. Even though, all the four schools of Tibetan Buddhism preach and practice the unsurpassable tantras, Nyingma School is exceptional in explaining the most secret teachings of Vajrayana through the three vehicles of Mahayoga, Anuyoga and Atiyoga.
The Mahayoga tantras are called Father Tantras and they include the sadhana practices of the Eight Herukas. They emphasize the profound aspect. The vast aspects are emphasized in the Seventeen Classes of Tantras of Illusory Net, the Eight Classes of Illusory Net and others.
The Anuyoga tantras are called Mother Tantras and they include Five Sutras including The General Sutra of Gathering Intentions.
The Atiyoga or Dzogchen Tantras are called Non-Dual Tantras and there are 64, 00,000 tantras in them.
Amongst these, the tantras that exist today are the Eighteen Mother Son Tantras as well as Two King Tantras belonging to the Outer Mental Class; Nine Great Expanse including White, Black and Striped Expanse belonging to the Inner Space Class; Seventeen tantras, Tantra of Troema, the Mantra Protectress and others belonging to the Secret Pith Instruction Class.
In order to preserve and spread the teachings of the Three Inner Tantras, five streams are necessary. They are the Stream of Empowerments, the source of blessings, the Stream of Oral Transmissions as a support, the Stream of Textual Explanation, the Stream of Aural Transmission of Pith Instructions and finally the Stream of Rituals to Accomplish Activities. Through the means of these five streams, the profound teachings of the Three Lineages which comes from the Primordial Buddha, Samantrabhadra, the Great Teacher to the present day teacher are being preserved and they are still alive in the minds of great teachers of older generation who live in India, Tibet, Nepal, Bhutan and other parts of the world.
If we, the new generation students fail to receive these transmissions from them, the teachings which are very rare, precious and profound might be lost forever from this world. Therefore, it is our responsibility to first receive the transmissions and then embark upon the practice of those teachings so that future sentient beings will be benefited.
The three inner tantras flourished in India on a limited scale. However, when these teachings reached Tibet through the blessings of Guru Rinpoche and other great masters, it is the fortune of the beings of Tibet that they spread extensively all over Tibet. Subsequently, the teachings developed into two main sections of teachings in the Nyingma School or the Earlier Translation School. They are Kama and Terma. Kama means the body of teachings translated chiefly during the period of Guru Rinpoche's stay in Tibet, first taught by Samantabhadra, the Primordial Buddha and then passed down from teacher to disciple uninterruptedly to this day.
Terma means the body of teachings transmitted through concealed treasures mainly hidden by Guru Rinpoche and Yeshe Tsogyal, to be discovered at the proper time by a 'terton,' a treasure revealer, for the benefit of future disciples.
Even though, the oral transmission of the Hundred Thousand Tantras of Nyingma School, discourses upon the root and explanatory tantras, empowerments of the rare Kama Teachings, as well as explanation and oral transmission of the back ground or supportive teachings mostly exist in the monasteries, however, there are still many teachings which have not been able to disseminate.
In terms of the explanatory discourses, within the Kama Teachings, there exist general commentaries upon the Eight Heruka Tantras and one hundred and thirty different commentaries to the Kagye Desheg Duipa (the Eight Herukas as the Condensed Essence of the Sugatas). Commentaries to the Heart Essence Tantra within the Illusory Net Tantra were made by King Dza, Indrabodhi, Gomi Deva, Nyi Od Senge, Buddhaguhya, Lalitavajra, Vimalamitra’s Gradual Path, Padmasambhava, Vairocana, Kawa Paltseg, Chogro Lui Gyaltsen, Namkhai Nyingpo, Nyak Gyanakumara, Nubchen Sangye Yeshe, Nubchung Yonten Gyatso, So Yeshe Wangchuk, Zurchen Shakya Jungne, Zurchung Sherab Drakpa, Sangdak Drophukpa, Dampa Desheg, Drolma Samdrup Dorje, Yungtonpa, Rongzompa, Longchen Rabjam, Mindroling brothers, Mipham and Dodrupchen. For example, even for a text like Manjusrinamasamgiti, extraordinary commentaries were made by Garab Dorje, Vimalamitra and Padmasambhava. Commentaries to the Anuyoga tantras were made by Chetsen Kye from Drusha, Nubchen Sangye Yesh, Kadampa Desheg and Khenpo Nuden. Commentaries to Dzogchen tantras were made by Garab Dorje, Manjushrimitra, Shrisimha, Jnanasutra, Vimalamitra, Padmasambhava, Rongzom Pandita and Longchenpa.
There also exist the commentaries to the profound teachings of the Three Tantras made by one hundred great treasure revealers and one thousand minor treasure revealers.
As such Kama teachings that has been passed down from the Primordial Buddha Samantabhadra to the present day teacher forms the foundation or the bedrock of all the Nyingma teachings and the Terma teachings revealed by successive tertons are like ornaments to the ocean of Kama teachings. Kama is the body and Terma is its parts. Kama is the root and Terma the branch.