Citta — rendered variously as ‘mind-stuff,’ ‘mental substance,’ or simply ‘mind’ — occupies a structural center in the depth-psychological reading of Patañjali’s Yoga Sūtras, where it designates neither a disembodied intellect nor a Cartesian res cogitans but a dynamic, material-processual substrate from which all mental activity emerges. Within the corpus, citta is treated as an evolute of prakṛti, composed of the three guṇas, and thus fundamentally distinct from puruṣa, the witnessing consciousness. The definitional tension most thoroughly elaborated is precisely this relation: citta modifies itself into the forms of perceived objects, yet it is not itself aware — its animation depends entirely on the reflected light of puruṣa. Bryant’s commentary, drawing on Vyāsa, Vācaspati Miśra, Vijñānabhikṣu, and Bhoja Rāja, makes plain that yoga is formally defined as the cessation (nirodha) of citta’s vṛttis — its permutations, thought-sequences, and cognitive states — including deep sleep. A further major axis concerns the ontological status of created minds (nirmāṇa-cittas) and the relationship between samskāra, vāsanā, and the citta as repository of subliminal impressions. The term thus serves as the decisive hinge between Sāṃkhya metaphysics and the practical psychology of liberation, and its correct understanding is prerequisite to grasping samādhi, kaivalya, and the entire soteriological arc of the Yoga school.