The tattva-traya (three realities) is the metaphysical cornerstone of Viśiṣṭādvaita, the philosophical school systematized by Śrī Rāmānuja. It holds that existence comprises three irreducible, co-eternal categories: (1) cit — sentient beings, namely the individual souls (jīvātmās), who are by nature knowing, blissful subjects; (2) acit — insentient matter (Prakṛti) and its transformations, which constitute the material universe; and (3) Īśvara — the Supreme Person, Bhagavān Nārāyaṇa, who is the inner controller (antaryāmin), the cause, and the final goal of all existence.
The defining insight of Viśiṣṭādvaita is that cit and acit are not independent absolutes but form the śarīra (body) of Īśvara, who is their inner soul (śarīrī). This śarīra-śarīrī (body-soul) relationship ensures that the multiplicity of souls and matter is real, not an illusion (thus rejecting Advaita's māyā), while Brahman remains the sole ultimate substance — hence viśiṣṭa (qualified) advaita (non-dualism).
Understanding tattva-traya is the first of the five artha-pañcakam truths that a mumukṣu (liberation-seeker) must know. It grounds all subsequent inquiry into the nature of the self (sva-svarūpa), God (Īśvara-svarūpa), the means of liberation (upāya), the goal (puruṣārtha), and the obstructions (virodhi). The classical Tamil work Tattva-traya by Piḷḷai Lokācārya is one of the most celebrated expositions of this doctrine.