<Li> Intrinsic existence: To account for the intrinsic existence of experience, a system constituted of elements in a state must exist intrinsically (be actual): specifically, in order to exist, it must have cause - effect power, as there is no point in assuming that something exists if nothing can make a difference to it, or if it cannot make a difference to anything . Moreover, to exist from its own intrinsic perspective, independent of external observers, a system of elements in a state must have cause - effect power upon itself, independent of extrinsic factors . Cause - effect power can be established by considering a cause - effect space with an axis for every possible state of the system in the past (causes) and future (effects). Within this space, it is enough to show that an "intervention" that sets the system in some initial state (cause), keeping the state of the elements outside the system fixed (background conditions), can lead with probability different from chance to its present state; conversely, setting the system to its present state leads with probability above chance to some other state (effect). </Li> <Li> Composition: The system must be structured: subsets of the elements constituting the system, composed in various combinations, also have cause - effect power within the system . Thus, if a system ABC is constituted of elements A, B, and C, any subset of elements (its power set), including A, B, C, AB, AC, BC, as well as the entire system, ABC, can compose a mechanism having cause - effect power . Composition allows for elementary (first - order) elements to form distinct higher - order mechanisms, and for multiple mechanisms to form a structure . </Li> <Li> Information: The system must specify a cause - effect structure that is the particular way it is: a specific set of specific cause - effect repertoires--thereby differing from other possible ones (differentiation). A cause - effect repertoire characterizes in full the cause - effect power of a mechanism within a system by making explicit all its cause - effect properties . It can be determined by perturbing the system in all possible ways to assess how a mechanism in its present state makes a difference to the probability of the past and future states of the system . Together, the cause - effect repertoires specified by each composition of elements within a system specify a cause - effect structure...</Li> <Li> Integration: The cause - effect structure specified by the system must be unified: it must be intrinsically irreducible to that specified by non-interdependent sub-systems obtained by unidirectional partitions . Partitions are taken unidirectionally to ensure that cause - effect power is intrinsically irreducible--from the system's intrinsic perspective--which implies that every part of the system must be able to both affect and be affected by the rest of the system . Intrinsic irreducibility can be measured as integrated information ("big phi" or Φ (\ textstyle \ Phi), a non-negative number), which quantifies to what extent the cause - effect structure specified by a system's elements changes if the system is partitioned (cut or reduced) along its minimum partition (the one that makes the least difference). By contrast, if a partition of the system makes no difference to its cause - effect structure, then the whole is reducible to those parts . If a whole has no cause - effect power above and beyond its parts, then there is no point in assuming that the whole exists in and of itself: thus, having irreducible cause - effect power is a further prerequisite for existence . This postulate also applies to individual mechanisms: a subset of elements can contribute a specific aspect of experience only if their combined cause - effect repertoire is irreducible by a minimum partition of the mechanism ("small phi" or φ (\ textstyle \ varphi)). </Li>

Integrated information theory of consciousness an updated account