IIT Expert

Glossary

Exclusion

The exclusion postulate requires that a substrate's cause–effect power be definite: it must specify its cause–effect state as this whole set of units. The set that qualifies is the one that is maximally irreducible, as measured by maximum system integrated information (φs*). That set is called a maximal substrate, or complex.

Exclusion fixes two things about a substrate. It fixes the borders: among candidate systems competing over overlapping units, the complex is the one with maximal φs, and overlapping candidates with lower φs are excluded from existence. It also fixes the grain, since the units constituting a system must themselves be definite. Across the possible micro- and macroscopic levels at which units could be defined, the winning grain is the one that maximizes φs for the entity whose units they are.

What exclusion does not fix is which cause–effect state a system specifies. That falls under the information postulate, which requires the substrate's cause–effect power to be specific, resolved by maximal intrinsic information. Exclusion does reach state at the level of a mechanism: mechanisms within a complex must specify a definite cause and effect, and the purview selected is the one over which integrated information is maximal.

Applied recursively, exclusion condenses a universe into a disjoint and exhaustive set of complexes. The substrate with maximum φs is identified as a complex, its units are excluded from further consideration, and the remaining units are searched for the next maximal substrate.

Ties are resolved by a cascade, and the terminal case disqualifies rather than decides. If overlapping candidate systems tie for maximal φs, the one with maximal structure integrated information Φ is chosen. If two or more also tie in Φ, those systems are held not to comply with the exclusion postulate: they do not qualify as complexes at all, and the next best system by φs that is unique is chosen instead.

The postulate is why consciousness on IIT's account has definite borders. The substrate that attains the maximum excludes the overlapping candidates that do not.

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