All Indian philosophical traditions are deeply engaged with ontology, the study of being, since clarity about the nature of reality is at the heart of three intimately connected goals: knowledge, proper conduct and liberation from the continued suffering that is part of all human existence. The formulation of a list of ontological categories, a classification of reality by division into several fundamental objective kinds, however, is less widespread. There is little room for a doctrine of distinct, if related, ontological categories in a philosophical school that takes reality as one, even less if that one lies beyond description. If the phenomenal world is but illusory appearance, as, for example, in the Vedānta of Śaṅkara, then a determination of kinds of entities does not recommend itself as a means to adequate analysis of the world. Even the Sāṅkhya tradition’s realism reduces the world to an evolution from two fundamental entities, spirit and matter. Categories make sense within the context of a pluralistic realism, an analysis of the world that finds it to be composed of a multiplicity of real entities. Such a view is found to some extent in Jaina philosophy, but is primarily defended and developed in the Nyāya-Vaiśeṣika school.
The Nyāya-Vaiśeṣika categories are seven: substance, quality, motion, universal, particular, inherence and not-being. While all are understood as real entities and objects of knowledge, substance is most fundamental as each of the others in some way depends on substance. Substances are nine: earth, water, fire, air, ether, time, space, self and mind. The first four are atomic: they may combine to form macroscopic substance, such as a clay pot, but in incomposite form they are indestructible atoms, as are the last two. Ether, time and space, likewise indestructible, are unitary and pervade all. In its irreducible parts, all substance is eternal; every composite whole is a destructible substance.
A relation of containment, called inherence, structures the categories. The qualities, actions and universals by which we might characterize a pot inhere in it. They are distinct entities from the pot, yet cannot exist apart from their underlying substrate. Composite substances like a pot are also contained in their parts by inherence, but the smallest parts, eternal substances, exist independently as receptacles that contain nothing. A whole, greater than the sum of its parts, is said to inhere in the parts while the parts are the inherence cause of the whole.
Eternal substance, the ultimate substrate of all, is a bare particular. An entity that is nothing but a receptacle for other entities, it furnishes criteria for separability and individuality, but cannot be defined in itself apart from others. This aspect of the concept of substance leads later Nyāya-Vaiśeṣika into extensive analysis of relations and negation.
Ontological Perspectivism and Geographical Categorizations