In ancient Indian philosophy, preliminary instances of atomism are found in the works of Vedic sage Aruni, who lived in the 8th century BCE, especially his proposition that "particles too small to be seen mass together into the substances and objects of experience" known as kaṇa. Although kana refers to "particles" not atoms (paramanu). Some scholars such as Hermann Jacobi and Randall Collins have compared Aruni to Thales of Miletus in their scientific methodology, calling them both as "primitive physicists" or "proto-materialist thinkers". Later, the Charvaka, and Ajivika schools of atomism originated as early as the 7th century BCE. Bhattacharya posits that Charvaka may have been one of several atheistic, materialist schools that existed in ancient India. Kanada founded the Vaisheshika school of Indian philosophy that also represents the earliest Indian natural philosophy. The Nyaya and Vaisheshika schools developed theories on how kaṇas combined into more complex objects.
Several of these doctrines of atomism are, in some respects, "suggestively similar" to that of Democritus. McEvilley (2002) assumes that such similarities are due to extensive cultural contact and diffusion, probably in both directions.
The Nyaya&ndash;Vaisesika school developed one of the earliest forms of atomism; scholars date the Nyaya and Vaisesika texts from the 9th to 4th centuries BCE. Vaisesika atomists posited the four elemental atom types, but in Vaisesika physics atoms had 25 different possible qualities, divided between general extensive properties and specific (intensive) properties. The Nyaya&ndash;Vaisesika atomists had elaborate theories of how atoms combine. In Vaisesika atomism, atoms first combine into s (triads) and  (dyad) before they aggregate into bodies of a kind that can be perceived.