Hindu philosophy
Vaiśeṣika metaphysical premises are founded on a form of atomism, that the reality is composed of four substances (earth, water, air, fire). Each of these four are of two types: atomic (paramāṇu) and composite. An atom is, according to Vaiśeṣika scholars, that which is indestructible (anitya), indivisible, and has a special kind of dimension, called “small” (aṇu). A composite, in this philosophy, is defined to be anything which is divisible into atoms. Whatever human beings perceive is composite, while atoms are invisible. The Vaiśeṣikas stated that size, form, truths and everything that human beings experience as a whole is a function of atoms, their number and their spatial arrangements, their guṇa (quality), karma (activity), sāmānya (commonness), viśeṣa (particularity) and amavāya (inherence, inseparable connectedness of everything).

Q: According to Vaisesika philosophy, how many substances comprise reality?
four