Vaisheshika presents a rigorously realist vision of the cosmos, in which reality is articulated through a set of fundamental categories and an atomistic account of the physical world. Central to this system is the doctrine of padārthas, or categories of being, which include substance (dravya), quality (guṇa), action (karma), generality (sāmānya), particularity (viśeṣa), and inherence (samavāya), with some traditions also recognizing non-existence (abhāva). These are not merely conceptual tools but are taken as objectively existing aspects of what is real, accessible through perception and inference. Substance, in particular, is elaborated as comprising nine eternal kinds: earth, water, fire, air, ether (ākāśa), time (kāla), space or direction (dik), self or soul (ātman), and mind (manas). Within this framework, universals and particulars are both affirmed as real, allowing for a nuanced account of how individual things can share common natures while remaining distinct.

The atomistic strand of Vaisheshika rests on the claim that the physical world is ultimately composed of indivisible, eternal atoms (paramāṇus), which are the smallest units of matter and cannot be further divided or destroyed. These atoms are of four basic types—earth, water, fire, and air—and their distinct and unchanging qualities underlie the diversity of material phenomena. Atoms combine through conjunction (saṃyoga) to form dyads, triads, and progressively larger aggregates, and they separate through disjunction (vibhāga); all gross objects are thus seen as impermanent configurations of eternal atomic constituents. Motion (karma) is indispensable in this process, as it initiates and sustains the combinations and separations that give rise to the observable world. Composite entities come into being and pass away, while the underlying atoms, along with souls, time, space, and ether, are held to be eternal.

This ontology is complemented by a robust epistemological realism and a subtle account of relations. Qualities such as color, taste, smell, touch, number, magnitude, conjunction, and disjunction are treated as real properties that inhere in substances and cannot exist independently of them. Inherence (samavāya) is posited as an irreducible, eternal relation that binds substances to their qualities, wholes to their parts, and universals to their instances, and is not to be confused with mere spatial contact. Particularity (viśeṣa) serves to individuate eternal entities, ensuring that distinct atoms or souls are not collapsed into a single undifferentiated reality. Knowledge gained through properly functioning perception and inference is regarded as generally veridical, disclosing a mind-independent world structured by these substances, qualities, and relations.

Later developments within the tradition often introduce a theistic dimension, bringing an ordering intelligence into this finely grained realist picture. In such accounts, Īśvara (God) does not create atoms ex nihilo but initiates their motion and arranges their combinations in accordance with karmic law, thereby sustaining cosmic order across cycles of creation and destruction. Within this vision, liberation is associated with right knowledge of these fundamental categories and of the true status of atoms and selves as eternal realities. The resulting worldview is one in which spiritual insight and metaphysical analysis converge, inviting a contemplative appreciation of a universe composed of enduring principles and ever-changing configurations.