Vaisheshika or Vaiśeṣika (Sanskrit: वैशेषिक) is one of the six schools of Indian philosophy (Vedic systems) from ancient India. In its early stages, the Vaiśeṣika was an independent philosophy with its own metaphysics, epistemology, logic, ethics, and soteriology. Over time, the Vaiśeṣika system became similar in its philosophical procedures, ethical conclusions and soteriology to the Nyāya school of Hinduism, but retained its difference in epistemology and metaphysics.
The epistemology of Vaiśeṣika school of Hinduism, like Buddhism, accepted only two reliable means to knowledge: perception and inference. Vaiśeṣika school and Buddhism both consider their respective scriptures as indisputable and valid means to knowledge, the difference being that the scriptures held to be a valid and reliable source by Vaiśeṣikas were the Vedas.
Vaisheshika school is known for its insights in naturalism. It is a form of atomism in natural philosophy. It postulated that all objects in the physical universe are reducible to paramāṇu (atoms), and one's experiences are derived from the interplay of substance (a function of atoms, their number and their spatial arrangements), quality, activity, commonness, particularity and inherence. Everything was composed of atoms, qualities emerged from aggregates of atoms, but the aggregation and nature of these atoms was predetermined by cosmic forces. Ajivika metaphysics included a theory of atoms which was later adapted in Vaiśeṣika school.
According to Vaiśeṣika school, knowledge and liberation were achievable by a complete understanding of the world of experience..
Although the Vaisheshika system developed independently from the Nyaya school of Hinduism, the two became similar and are often studied together. In its classical form, however, the Vaishesika school differed from the Nyaya in one crucial respect: where Nyaya accepted four sources of valid knowledge, the Vaishesika accepted only two.
Vaisheshika espouses a form of atomism, that the reality is composed of five substances (examples are earth, water, air, fire, and space). Each of these five are of two types, explains Ganeri, (paramāṇu) and composite. A paramāṇu is that which is indestructible, indivisible, and has a special kind of dimension, called “small” (aṇu). A composite is that which is divisible into paramāṇu. Whatever human beings perceive is composite, and even the smallest perceptible thing, namely, a fleck of dust, has parts, which are therefore invisible. The Vaiśeṣikas visualized the smallest composite thing as a “triad” (tryaṇuka) with three parts, each part with a “dyad” (dyaṇuka). Vaiśeṣikas believed that a dyad has two parts, each of which is an atom. Size, form, truths and everything that human beings experience as a whole is a function of parmanus, their number and their spatial arrangements.
Parama means "most distant, remotest, extreme, last" and aṇu means "atom, very small particle", hence paramāṇu is essentially "the most distant or last small (i.e. smallest) particle".
Vaisheshika postulated that what one experiences is derived from dravya (substance: a function of atoms, their number and their spatial arrangements), guna (quality), karma (activity), samanya (commonness), vishesha (particularity) and nsamavaya (inherence, inseparable connectedness of everything).
Hinduism identifies six Pramāṇas as epistemically reliable means to accurate knowledge and to truths: Pratyakṣa (perception), Anumāna (inference), Upamāna (comparison and analogy), Arthāpatti (postulation, derivation from circumstances), Anupalabdhi (non-perception, negative/cognitive proof) and Śabda (word, testimony of past or present reliable experts). Of these Vaiśeṣika epistemology considered only pratyakṣa (perception) and anumāna (inference) as reliable means of valid knowledge. Nyaya school, related to Vaiśeṣika, accepts four out of these six.
The earliest systematic exposition of the Vaisheshika is found in the Vaiśeṣika Sūtra of Kaṇāda (or Kaṇabhaksha). This treatise is divided into ten books. The two commentaries on the Vaiśeṣika Sūtra, Rāvaṇabhāṣya and Bhāradvājavṛtti are no more extant. Praśastapāda’s Padārthadharmasaṁgraha (c. 4th century) is the next important work of this school. Though commonly known as bhāṣya of Vaiśeṣika Sūtra, this treatise is basically an independent work on the subject. The next Vaisheshika treatise, Candra’s Daśapadārthaśāstra (648) based on Praśastapāda’s treatise is available only in Chinese translation. The earliest commentary available on Praśastapāda’s treatise is Vyomaśiva’s Vyomavatī (8th century). The other three commentaries are Śridhara’s Nyāyakandalī (991), Udayana’s Kiranāvali (10th century) and Śrivatsa’s Līlāvatī (11th century). Śivāditya’s Saptapadārthī which also belongs to the same period, presents the Nyāya and the Vaiśeṣika principles as a part of one whole. Śaṁkara Miśra’s Upaskāra on Vaiśeṣika Sūtra is also an important work.
According to the Vaisheshika school, all things that exist, that can be cognized and named are padārthas (literal meaning: the meaning of a word), the objects of experience. All objects of experience can be classified into six categories, dravya (substance), guṇa (quality), karma (activity), sāmānya (generality), viśeṣa (particularity) and samavāya (inherence). Later Vaiśeṣikas (Śrīdhara and Udayana and Śivāditya) added one more category abhava (non-existence). The first three categories are defined as artha (which can perceived) and they have real objective existence. The last three categories are defined as budhyapekṣam (product of intellectual discrimination) and they are logical categories.
According to the Vaiśeṣika school, the trasareṇu are the smallest mahat (perceivable) particles and defined as tryaṇukas (triads). These are made of three parts, each of which are defined as dvyaṇuka (dyad). The dvyaṇukas are conceived as made of two parts, each of which are defined as paramāṇu (atom). The paramāṇus (atoms) are indivisible and eternal, they can neither be created nor destroyed. Each paramāṇu (atom) possesses its own distinct viśeṣa (individuality).
The measure of the partless atoms is known as parimaṇḍala parimāṇa. It is eternal and it cannot generate the measure of any other substance. Its measure is its own absolutely.
The early Vaiśeṣika texts presented the following syllogism to prove that all objects i.e. the four bhūtas, pṛthvī (earth), ap (water), tejas (fire) and vāyu (air) are made of indivisible paramāṇus (atoms): Assume that the matter is not made of indivisible atoms, and that it is continuous. Take a stone. One can divide this up into infinitely many pieces (since matter is continuous). Now, the Himalayan mountain range also has infinitely many pieces, so one may build another Himalayan mountain range with the infinite number of pieces that one has. One begins with a stone and ends up with the Himalayas, which is a paradox - so the original assumption that matter is continuous must be wrong, and so all objects must be made up of a finite number of paramāṇus (atoms).