The Nyaya system of Indian philosophy is a system of dualistic realism, and like all other dualistic systems it has very likely been founded on a Rk. ascribed to the seer Dirghatamas. The Rk. in question says, - two birds, intimate friends, take shelter in the same tree. One of them eats the sweet berries, the other without eating perches, looking on (Dca suparna sayuja sakhaya, etc. Rgveda, i. 164. 20). Here, we find a reference to the supreme soul and the individual soul. This Rk. is the authority on dualism. Dualistic philosophers have all taken recourse to this verse to distinguish the individual soul from the supreme entity. In the Nyaya system (as also in other Indian logical systems) a syllogistic argument is generally advanced with the proposition the mountain is fiery, because of smoke (Parvato vahniman dhumat).