Integrated Information Theory (IIT) proposes that consciousness is identical to integrated information, a quantity ('phi') that measures the amount of irreducible cause-effect power in a system.

Developed by Giulio Tononi and collaborators, IIT attempts to provide a fundamental account of what consciousness *is* and how it can be measured. It posits that a system is conscious if it has a large repertoire of states (information) and if these states are highly interconnected and mutually dependent (integrated). The theory suggests that consciousness is not merely about having information, but about the *integration* of that information into a unified, irreducible whole that cannot be broken down into independent components. IIT offers specific postulates, such as consciousness being intrinsic (existing for itself), structured (composed of distinctions), and specific (each experience is unique). While mathematically complex and still under active development and debate, IIT provides a framework for both identifying conscious systems (even non-biological ones) and for understanding the level and nature of their consciousness. It suggests that consciousness is a fundamental property of specific physical systems that meet certain informational criteria, rather than an emergent property of computation alone.