Mindstream (citta-santāna) in Buddhist philosophy is the moment-to-moment continuum (Sanskrit: saṃtāna) of awareness which provides a continuity from one life to another.
The concept developed in later Yogacara, to avoid reification of the ālaya-vijñāna.
Citta-saṃtāna (Sanskrit), literally "the stream of mind", is the stream of succeeding moments of mind or awareness.
It provides a continuity of the personality in the absence of a permanently abiding "self" (ātman), which Buddhism denies.
The mindstream provides a continuity from one life to another, akin to the flame of a candle which may be passed from one candle to another:
Indian Buddhists see the 'evolution' of mind i[n] terms of the continuity of individual mind-streams from one lifetime to the next, with karma as the basic causal mechanism whereby transformations are transmitted from one life to the next.
According to Waldron,
The mind stream (santāna) increases gradually by the mental afflictions (kleśa) and by actions (karma), and goes again to the next world. In this way the circle of existence is without beginning."
The vāsanās (karmic imprints) provide the karmic continuity between lives and between moments.
According to Lusthaus, these vasanas determine how one...actually sees and experiences the world in certain ways, and one actually becomes a certain type of person, embodying certain theories which immediately shape the manner in which we experience.
Citta holds the semantic field of "that which is conscious", "the act of mental apprehension known as ordinary consciousness", "the conventional and relative mind/heart".
Citta has two aspects:
"...Its two aspects are attending to and collecting of impressions or traces (Sanskrit: vāsanā) cf. vijñāna." Saṃtāna or santāna (Sanskrit) holds the semantic field of "eternal", "continuum", "a series of momentary events" or "life-stream".
Citta is often rendered as sems in Tibetan and saṃtāna corresponds to rgyud, which holds the semantic field of "continuum", "stream", and "thread" Citta-saṃtāna is therefore rendered sems rgyud.
Rgyud is the term that Tibetan translators (Tibetan: lotsawa) employed to render the Sanskrit term "tantra".
Thugs-rgyud is a synonym for sems rgyud Thugs holds the semantic field:
"primordial state, experience)",
"feelings" and is sometimes a homonym of "citta" (Sanskrit).
Thugs-rgyud holds the semantic field "wisdom", "transmission", "heart-mind continuum", "mind", "continuum stream of mind" and "nature of mind."
Chinese, Korean and Japanese
The Chinese equivalent of Sanskrit citta-saṃtāna and Tibetan sems-kyi rgyud ("mindstream") is xin xiangxu (simplified Chinese: 心相续; traditional Chinese: 心相續; pinyin: xīn xiāngxù; Wade–Giles: hsin hsiang-hsü).
According to the Digital Dictionary of Buddhism, xīn xiāngxù means "continuance of the mental stream" (from Sanskrit citta-saṃtāna or citta-saṃtati), contrasted with wú xiàngxù 無相續 "no continuity of the mental stream" (from asaṃtāna or asaṃdhi) and shì xiāngxù 識相續 "stream of consciousness" (from vijñāna-saṃtāna).
This compound combines xin 心 "heart; mind; thought; conscience; core" and xiangxu "succeed each other", with xiang 相 "each other; one another; mutual; reciprocal" and xu 續 or 续 "continue; carry on; succeed". Thus it means "thoughts succeeding each other".
Xin xiangxu is pronounced sim sangsok in Korean and shin sōzoku in Japanese.
Origins and development
The notion of citta-santāna developed in later Yogacara-thought, where citta-santāna replaced the notion of ālayavijñāna, the store-house consciousness in which the karmic seeds were stored.
It is not a "permanent, unchanging, transmigrating entity", like the atman, but a series of momentary consciousnesses.
Lusthaus describes the development and doctrinal relationships of the store consciousness (ālaya-vijñāna) and Buddha nature (tathāgatagarbha) in Yogācāra.
To avoid reification of the ālaya-vijñāna,
The logico-epistemological wing in part sidestepped the critique by using the term citta-santāna, "mind-stream", instead of ālaya-vijñāna, for what amounted to roughly the same idea.
It was easier to deny that a "stream" represented a reified self.
Dharmakīrti (fl. 7th century) wrote a treatise on the nature of the mindstream in his Substantiation of Other Mindstreams (Saṃtãnãntarasiddhi).
According to Dharmakirti the mindstream was beginningless temporal sequence.
The notion of mindstream was further developed in Vajrayāna (tantric Buddhism), where "mindstream" (sems-rgyud) may be understood as a stream of succeeding moments, within a lifetime, but also in-between lifetimes.
The 14th Dalai Lama holds it to be a continuum of consciousness, extending over succeeding lifetimes, though without a self or soul.
Wikipedia:Flow of consciousness