Abstract : The nerve nets or automata as developed in the theories of McCulloch and Shannon exhibit a two valued extensional logic; i.e., Boolean algebra or a variation of it. The results of this mathematical and logical model are only applica ble to a limited degree to the actual function ing of living organisms. Deductive logic is primarily designed to analyze and verify thought processes, not to represent them. Especially the assumed equality of all statements according to their truth value and the paradoxes of mate rial implication hinder the ability of the theory to living systems. Modal and intensional logic, with the introduction of the operators of possibility and necessity, the function of strict implication, and the assignment of several truth values approximates thought processes more closely. Thus a nerve net functioning according to modal logic would be a better model of a living system. Several systems were examined for representation in a nerve net and Prior's system Q was selected as the most appropriate.