In Jain metaphysics jiva is the soul or living substance, one of the two fundamental categories of reality alongside ajiva, the non-living. A jiva is characterised by consciousness, and Jainism holds that jivas are infinite in number, individual, eternal, and neither created nor destructible.
Two features are distinctive. The Jain soul is coextensive with the body it occupies, expanding and contracting to fill it as a lamp's light fills whatever room it is placed in, so that the soul of an elephant and the soul of an ant are the same kind of substance at different extensions. And its innate nature is infinite knowledge, infinite perception, infinite bliss and infinite energy: these are not potentials to be developed but properties currently obscured by karmic matter.
Jainism classifies living beings by the number of senses they possess, and the scheme governs an enormous amount of practice. One-sensed beings, possessing touch alone, include the beings held to inhabit earth, water, fire and air, and all plants. Two-sensed beings add taste, three-sensed smell, four-sensed sight, and five-sensed hearing, the last category including humans, gods, hell-beings and the higher animals, some of which are also credited with mind. Because harming any of these binds karma, and because the scale grades the severity, the classification directly generates Jain dietary rules, occupational restrictions and ascetic disciplines. It also marks how unusually wide the Jain attribution of life is: that fire and air are alive is a Jain position not shared by the other Indian schools.
Jivas are further divided into the liberated and the bound. The liberated, having shed all karma, rise to the summit of the occupied universe, the Siddhashila, where they remain permanently in their own nature, individually distinct, omniscient, and without further interaction with the world.
That the liberated remain plural and individual, rather than merging into a single reality, is among the sharpest differences between Jainism and Advaita Vedanta, and it follows directly from the Jain insistence that each soul is an independent substance rather than a portion or reflection of anything else.