Jain biology is a graded ontology of souls and the entire ethic is calculated from it. Ekendriya, one-sensed beings, possess only touch and comprise earth-bodied, water-bodied, fire-bodied, air-bodied and plant-bodied life; nigoda are microscopic beings in colonies of infinite number occupying a single body. Two-sensed beings add taste — worms, leeches; three-sensed add smell — ants, lice; four-sensed add sight — flies, bees; five-sensed add hearing and include animals, humans, hell-beings and gods, with the highest also possessing mind. Killing a five-sensed being binds vastly more karma than killing a one-sensed one, and the practical ethics is therefore not the impossible avoidance of all harm but the systematic minimisation of it: eat plants rather than animals, above-ground plants rather than roots, do not eat at night, filter water, do not take up trades that require mass killing. The system is explicit that a householder cannot avoid himsa and does not pretend otherwise. What it offers is a calculus, and the calculus is applied with a rigour no other tradition attempts.