In a dream, is knowing that one is dreaming the self-validating cognition (svasaṃvedana) of mind consciousness or the self-cognition (svasaṃvitti)?

The self-validating cognition (svasaṃvedana) is the introspective observation of the consciousness-mind itself and its own mental factors; "itself" means the mind consciousness discerning the mind consciousness, the manas discerning the manas, the five consciousnesses discerning the five consciousnesses — it does not mean mutual discernment. The self-cognition (svasaṃvitti) is the consciousness-mind's discernment of the object-aspect (nimitta) realm; this object-aspect includes all dharmas, and of course also includes the eighth consciousness and its mental factors — it just depends on how capable the discerning wisdom is. Dream refers to the dream-scape, which is the object-aspect; knowing is the perceiving-aspect (darśana-bhāga) of the consciousness-mind. When the consciousness-mind discerns sense-objects, that is the perceiving-aspect discerning the object-aspect, which is self-cognition, not self-validating cognition; the perceiving-aspect seeing itself is self-validating cognition. Only when the perceiving-aspect and the object-aspect are combined do self-cognition and self-validating cognition arise; self-validating cognition is actually one kind of self-cognition, except that the object-aspect has become the consciousness-mind itself, with itself and its mental factors serving as the object-aspect. 

The perceiving-aspect that discerns the dream-scape object-aspect is the perceiving-aspect of the sixth and seventh consciousnesses, and the sixth consciousness is the solitary consciousness (mano-vijñāna-eka-citta). Seeing all realms is mainly the seeing of the sixth and seventh consciousnesses; what sentient beings can feel and observe is only the seeing of the mind consciousness — the seeing of the seventh consciousness cannot be perceived. For now, let us speak of the seeing of the mind consciousness. When asleep and dreaming, why does the solitary consciousness not know that it is dreaming? Because in the dream the mind consciousness is dull and unclear; sleep itself is a hindrance, an obscuration that veils the wisdom-cognition of the mind consciousness. 

When the hindrance of sleep is removed and there is no obscuration, the mind consciousness becomes clear and lucid, and one will attain the dhyāna of the first meditation; or, conversely, as meditative concentration grows ever deeper, sleep will become ever less and ever lighter, so that in dreams the mind consciousness becomes increasingly lucid, to the point of clearly knowing that one is dreaming, and one will not create unwholesome karma in the dream, and may even perform wholesome karma. Therefore, knowing one is dreaming within a dream shows that the sixth and seventh consciousnesses possess meditative concentration and wisdom, and that the hindrance of sleep is slight. Not knowing one is dreaming within a dream means that the conscious nature of the sixth and seventh consciousnesses is veiled by sleep, and the mind is not clear and lucid.

The knowing and seeing within a dream is the perceiving-aspect of the solitary consciousness; the manas has a great influence on the seeing of the mind consciousness, but we will not discuss the specific influence here. Within a dream, the solitary consciousness's discernment of realms is limited, not as comprehensive and clear as the discernment of the consciousness accompanied by the five senses (pañca-sahagata-mano-vijñāna), which is aided by the five consciousnesses. Not knowing one is dreaming within a dream is because the self-cognition function of the solitary consciousness is incomplete and its power of wisdom is weak; this is related to the physical body and the manas. The strength of all the discernment functions of the mind consciousness is related not only to its own meditative concentration and wisdom, but also to the meditative concentration and wisdom of the manas, and to the physical body; one cannot discuss the functions of the mind consciousness apart from the physical body and the manas.

Why is it related to the physical body? Everyone knows the principle that the mind consciousness's awareness while awake is influenced by the physical body. During sleep, the manas does not wish to discern realms, so none of the six consciousnesses arise; while dreaming, the solitary consciousness is compelled to arise and discern the dream-scape, but because the nervous system's activity is relatively sluggish, the mind consciousness's thinking is suppressed, its cognitive wisdom is relatively low, and it cannot distinguish that the realm it faces is a dream, so it takes the dream to be reality. This is the same as the situation when drunk — both are caused by the nervous system not being active and alert.

If, within a dream, the mind consciousness has self-validating cognition, that means the mind consciousness can know itself and its mental factors — this is the power of introspection (pratyavekṣā-bala), which requires even stronger meditative concentration and wisdom than the mind consciousness's knowing of sense-object realms, and is more difficult. If, within a dream, the mind consciousness's self-cognition function is insufficient, its self-validating cognition function is almost nonexistent, and it will not validate itself; therefore it cannot introspect — unless one is a person with excellent meditative concentration, a person with strong awareness. For those who possess the four dhyānas and eight samādhis, the power of introspection within dreams is even better.

The strength of the various functions of the mind consciousness is not only a matter of its own meditative concentration and wisdom, but is even more related to the manas. Although from ancient times to the present almost no one has been able to recognize and observe this issue, the functions of the mind consciousness are indeed inseparable from the manas; the two complement each other. To discuss the mind consciousness apart from the manas is to abandon the root and chase the branches.