thig) and (iv) the Seminal Heart system of Padmasambhava (mKha' 'gro snying thig)." Longchenpa's Dzogchen philosophy is based on the Dzogchen view outlined in these tantric texts. This worldview sees all phenomena (dharmas, Tib. chos) as the emanations or expressions (rtsal), displays (rol pa), and adornments (rgyan) of an ultimate nature or principle (Dharmatā, Tib. chos nyid, or Dharmadhātu, Tib. chos kyi dbyings) This ultimate principle is described in various ways by Longchenpa, using terminology that is unique to Dzogchen, such as the basis or ground (ghzi) or the "nature of mind" (sems nyid). Longchenpa describes this fundamental basis as being primordially pure and empty while also having the nature of a subtle self-arising awareness. This empty and spontaneous primordial glow (ye gdangs) is the subtle basis for the arising of all phenomenal appearances. Longchenpa brought Dzogchen thought more closely into dialogue with scholastic Buddhist philosophy and the Sarma tantric systems which were normative in the Tibetan academic institutions of his time. One of Longchenpa's main motivations was to provide a learned defense of Dzogchen thought and practice. Longchenpa's writings also intent to prove the overall superiority of the Dzogchen path over the other eight vehicles of sutra and tantra. His work also posits that this supreme Dzogchen view is not just the pinnacle of Buddhism (which Longchenpa compares the peak of a mountain), but it is in fact a keystone to the entire Buddhist Dharma, without which the "lower vehicles" cannot be fully understood or justified (just like one cannot see the entirety of a mountain unless one is at the top). In his Theg mchog mdzod, Longchenpa also provides an extensive doxography of Buddhism (based on the nine yanas) in order to explain why Dzogchen (i.e. Atiyoga) deserves the highest rank in this doxography. Longchenpa's understanding of the relationship between Dzogchen and the lower vehicles is inclusive, and he sees Dzogchen as embracing all of the eight vehicles while also sublimating and transcending them. Dzogchen practice Longchenpa categorized Dzogchen as a teaching within "secret mantra" (Vajrayana), and specifically, he considered it to be part of the perfection stage of secret mantra practice, defining this "great perfection phase" (rdzogs rim chenpo), as "resting in the pristine unfabricated enlightening-mind of awareness" (in his bSam gtan ngal gso 80.2). Furthermore, Longchenpa defended the validity of Dzogchen as a stand alone system of formless and effortless perfection stage practice, which did not