Jiva is the Sanskrit term for the soul or living substance, and it stands as the first and most important of the Jain tattvas. Unlike materialist systems that reduce consciousness to the body, and unlike monist traditions that dissolve all souls into a single universal spirit, Jainism affirms that there are infinitely many distinct, individual souls, each eternal, uncreated, and indestructible. The jiva has no beginning and no end; it was never made and can never be annihilated.
The essential characteristic of the jiva is consciousness, expressed through upayoga, the functioning of awareness. Upayoga has two aspects: jnana, or determinate knowledge, and darshana, or indeterminate apprehension and perception. Every soul, however deeply buried in karma, retains at least a trace of consciousness, for consciousness is not an acquired property but the very nature of the soul. In its pure and unobstructed condition, the jiva possesses ananta chatushtaya, the four infinitudes: infinite knowledge (ananta jnana), infinite perception (ananta darshana), infinite bliss (ananta sukha), and infinite energy (ananta virya).
Jain metaphysics describes the soul as having a further remarkable trait: it is capable of contraction and expansion to fill the body it occupies, much as a lamp illumines the whole room in which it is placed. The soul is thus coextensive with its body, neither an infinitesimal point nor an all-pervading infinity, but pervading exactly the frame it animates. This doctrine allows the same soul to inhabit the tiny body of an insect in one life and a large body in another.
Souls are broadly divided into two great classes. The mundane or embodied souls are the samsari jivas, still bound by karma and wandering through the cycle of rebirth. The liberated souls are the mukta or siddha jivas, wholly freed from karma and dwelling eternally at the apex of the cosmos in perfect bliss. Among the samsari jivas, a detailed classification proceeds according to the number of senses a being possesses. Ekendriya beings have only the sense of touch and include earth-bodied, water-bodied, fire-bodied, air-bodied, and plant-bodied life, the last called nigoda in its most rudimentary form. Beings with two senses add taste, those with three add smell, those with four add sight, and those with five, the panchendriya, add hearing.
The five-sensed beings include denizens of the hells, animals of higher order, human beings, and celestial beings. Among these, some possess mind, the internal organ called manas, and are termed samjni, capable of reasoning and reflection, while others lack it and are asamjni. It is chiefly the rational human birth that affords the opportunity for spiritual effort leading toward liberation.
A distinctive and deeply ethical implication follows from this analysis. Because life is graded and present even in the elements and in plants, the Jain principle of ahimsa, non-violence, extends to all sentient beings and demands the utmost care in conduct. The recognition that every jiva, however humble, harbors the same infinite potential for enlightenment underlies the tradition's reverence for all life.
The jiva, then, is not a passive substrate but an active agent that binds karma through its passions and can, by its own disciplined effort, cast that karma off. The whole of the Jain path is the story of the jiva rediscovering its own innate purity, shedding the accreted matter that veils its infinite faculties, and returning at last to the luminous, autonomous existence that was always its true nature.