“According to Dam-tsik-dor-jay, a Mongolian from Kalka, when the [tantric] view of the Great Perfection is taught, it also is divided into two categories, objective and subjective. The former can be understood in the vocabulary of the New Translation Schools [Kagyud, Sakya, & Gelug], just explained, as the objective clear light, that is to say, as emptiness which is the object of a wisdom consciousness. In the Great Perfection [tantras of the Nyingma school,] the term ‘view’ most frequently refers not to the object emptiness, but to the subject, the wisdom consciousness and , more or less, a union of the object – emptiness – with the subject – the wisdom consciousness realizing it. This innate fundamental mind of clear light is emphasized equally in the Highest Yoga Tantra systems of the New Translation Schools and in the Nying-ma system of the Great Perfection and is the proper place of comparison of the old and new schools.
In the Great Perfection, however, the subjective view, that is to say, the mind which takes emptiness as its object – is not the ordinary of coarse mind described in the Perfection Vehicle of the Great Vehicle but a subtle mind. It is basic knowledge (rig pa), clear light (‘od gsal), the fundamental innate mind of clear light (gnyug ma lhan cig skyes pa’i ‘od gsal) which is the final status (gnas lugs) of things…
The fundamental mind which serves as the basis of all phenomena of cyclic existence and nirvana is posited as the ultimate truth or nature of phenomena (dharmata, chos nyid); it is also called the ‘clear light’ (abhasvara, ‘od gsal) and uncompounded (asamskrta, ‘dus ma byas). In Nying-ma it is called the ‘mind-vajra’; this is not the mind that is contrasted with basic knowledge (rig pa) and mind (sems) but the factor of mere luminosity and knowing, basic knowledge itself. This is the final root of all minds, forever indestructible, immutable, and unbreakable continuum like a vajra. Just as the New Translation Schools posit a beginningless and endless fundamental mind, so Nying-ma posits a mind-vajra which has no beginning or end and proceeds without interruption through the effect stage of Buddhahood. It is considered ‘permanent’ in the sense of abiding forever and thus is presented as a permanent mind. It is permanent not in the sense of not disintegrating moment by moment but in the sense that its continuum is no interrupted…
With respect to identifying the clear light in the Great Perfection: when, for instance, one hears a noise, between the time of hearing it and conceptualizing it as such and such, there is a type of mind devoid of conceptuality but nevertheless not like sleep or samadhi, in which the object is a reflection of this entity of mere luminosity and knowing. It is at such a point that the basic entity of the mind [clear light] is identified.
“Union of new Old Schools” in Kindness, Clarity, & Insight (trans. Hopkins)