The subtlest mind (sems shin-tu phra-mo), known as the clear-light mind (‘od-gsal), has uninterrupted continuity, with no beginning and no end, even when enlightened. Before enlightenment, it is manifest (mngon-‘gyur-ba) automatically for a tiny moment at death. In meditation, it can be made manifest when all the grosser levels of mental activity have been temporarily ceased by means of several different anuttarayoga methods.
At such manifest times before enlightenment, the clear light subtlest level of mind takes as its object an appearance similar to that which appears when one cognizes voidness – a bareness that is the deep blue color that appears in the sky just before it gets light at dawn, when the sky is devoid of sunlight, moonlight, starlight, and complete darkness. This is the explanation given by Kedrub Norzang Gyatso (mKhas-grub Nor-bzang rgya-mtsho). Some other scholars assert that the manifest clear light mind at such times functions as both a consciousness and as an object of consciousness, but not in the manner of reflexive awareness (rang-rig) as asserted by the Sautrantika, Chittamatra, and Yogachara-Svatantrika tenet systems. When enlightened, the clear light mind becomes omniscient awareness (rnam-mkhyen) of the two truths: the extent of what exists (ji-snyed-pa) and the way in which everything exists (ji-lta-ba).
While grosser levels of consciousness are manifest, the clear light mind continues as a dormant factor (bag-la nyal). According to the Jetsunpa (rJe-btsun Chos-kyi rgyal-mtshan) textbook tradition, “dormant” in this context means that clear light mind continues as a subliminal awareness (bag-la nyal). As such, it still gives rise to and cognizes an appearance like that of voidness, but the person (gang-zag) does not cognize it. According to the Panchen (Pan-chen bSod-nams grags-pa) textbook tradition, during dormant phases, clear light mind continues in the manner of a constant habit (bag-chags). At such times, because it is not actively taking any object, clear light mind is a noncongruent affecting variable (ldan-min ‘du-byed) and not a way of knowing something,. The Panchen tradition does not assert subliminal awareness. If it is a way of knowing something, it must be manifest.
[See: Dormant Grasping for True Existence: Gelug Madhyamaka. See also: Congruent and Noncongruent Affecting Variables]