Integrated Information Theory

Integrated Information Theory (IIT) is a mathematical theory of Consciousness developed by Giulio Tononi, proposing that conscious experience is identical to a specific type of information structure. The theory's central quantity, Φ (phi), measures the degree to which a system is simultaneously differentiated (information-rich) and integrated (irreducible to independent parts).

IIT is distinctive among theories of consciousness for two reasons. First, it starts from the phenomenology — from axioms about what experience is like (existence, composition, information, integration, exclusion) — and derives physical requirements, rather than starting from neural mechanisms and hoping consciousness falls out. Second, it yields a quantity: consciousness is not binary but graded, and Φ provides (in principle) a measure on a ratio scale. This connects consciousness directly to Information Theory and Mathematics, making it the most formally ambitious theory in the field.

The theory's most provocative implication is panpsychism: since Φ can be nonzero for any system with the right causal architecture, even simple physical systems may possess minimal experience. Whether this is an insight or a reductio ad absurdum depends on whether one treats Consciousness as a binary threshold phenomenon or a continuous feature of physical reality. IIT bets everything on the latter.