The Indian systems of metaphysics known as ‘darśanas’ invariably deal with three topics: Pramā (valid knowledge), pramāṇa (means of valid knowledge) and prameya (objects of valid knowledge)
The Viśiṣṭādvaita Darśana, one of the important schools of Vedānta, whose chief exponent was Rāmānuja (A. D. 1017-1137) categorises prameya into two broad groups of ‘dravya’ (substance) and ‘adravya’ (nonsubstance).
If dravya acts as a substratum or locus of change, adravya is an attribute or quality always necessarily dependent on dravya. Neither dravya nor adravya can be thought of apart from the other.
The adravyas are ten: sattva, rajas and tamas (the three guṇas or qualities of prakṛti or insentient nature); śabda (sound), sparśa (touch), rūpa (colour or form), rasa (taste) and gandha (odour) being the five characteristic qualities of the five bhūtas like ākāśa (ether); saṁyoga (conjunction or external relation between substances) and śakti (potency or the effecting agency in all causal substances as for instance, plasticity in clay or the power of attraction in a magnet).
According to Viśiṣṭādvaita, instances can be given where an adravya can be viewed both as a substance and as an attribute. For example, though light is an attribute of an effulgent object, it serves also as a substance, since it is subject to contraction and diffusion, and possesses colour as an attribute. Dharmabhūtajñāna is another example.