Seven padārthas — the inventory of existence

All of reality falls under seven irreducible categories: dravya (substance — 9 types: earth, water, fire, air, ether, time, space, ātman, manas), guṇa (quality — 24 types), karma (motion — 5 types), sāmānya (universal), viśeṣa (ultimate differentiator), samavāya (inherence), and abhāva (absence). The first three are positive existents; the next three govern universals, particulars, and relations; abhāva formalises the ontology of negation.

The category of viśeṣa (ultimate particularity) is Vaiśeṣika's most original contribution. Two atoms of the same element are qualitatively identical. What makes them numerically distinct? Each possesses its own irreducible viśeṣa — a bare "thisness" (haecceity in Scotist terms) grounding numerical difference without qualitative difference.

Atomic theory — paramāṇuvāda

Physical reality is ultimately composed of eternal, indivisible, partless atoms (paramāṇu) of four elemental types: earth (pārthiva), water (āpya), fire (tejas), air (vāyavya). Ether, time, space, ātman, and manas are also dravyas but are all-pervading rather than atomic. Each elemental atom carries a primary quality as its locus: earth-atoms have smell (gandha), water-atoms taste (rasa), fire-atoms colour (rūpa), air-atoms touch (sparśa).

The Vaiśeṣika atomic argument: "if matter were infinitely divisible, no real macroscopic aggregates would exist — the whole would equal its infinitely divisible parts, and no new wholes could emerge." The argument concerns conditions for the existence of composite entities (avayavin), not empirical indivisibility.

Samavāya — inherence and its critics

Samavāya is the inseparable relation between a substance and its qualities, a whole and its parts, a universal and its instances. Unlike conjunction (saṃyoga, a separable relation), samavāya is constitutive. It is posited as a single eternal omnipresent entity — a padārtha in its own right. Critics pressed the regress: does samavāya itself inhere via a second-order samavāya? Vaiśeṣika's reply: samavāya is svāśrayavṛtti — self-relating, requiring no further relation.

Śaṃkara's Advaita attack on samavāya is one of the sharpest arguments in the Brahmasūtrabhāṣya: if the cloth-thread relation requires samavāya, and samavāya requires a further relation, infinite regress follows — unless identity (tādātmya) is the ground. For Advaita all relations reduce to identity.

Liberation — ātman's reversion to natural state

The Vaiśeṣika ātman is philosophically unusual: unconscious by nature, becoming conscious only when joined with manas. Consciousness is thus a contingent relational quality of the ātman — not its essence. Liberation is the permanent separation of ātman from manas — cessation of all pleasure and pain — the ātman reverts to its natural unconscious state. Īśvara is the nimittakāraṇa (efficient cause) of creation but not the material cause.

The unconscious-ātman thesis sets Vaiśeṣika apart from every other āstika school. In Sāṃkhya, Puruṣa is pure consciousness by nature. In Advaita, Brahman = cit as absolute substrate. Only Vaiśeṣika makes consciousness a relational emergent. This position was criticised by all: if the liberated ātman is unconscious, in what sense is liberation a good?