In the present article, we have tried to advance a better philosophical understanding of IIT 4.0, centred on the apparent tension between its idealistic ontology and realism. After presenting the fundamentals of the theory (Section 2), we argued that IIT’s idealistic ontology should be understood as a combination of phenomenal primitivism, reductionism regarding Φ-structures and physical substrates of consciousness (PSCs), and eliminativism about non-conscious physical entities (Section 3). That is, the theory’s ontology asserts that only experiences ultimately exist, but that these can also be described and purportedly explained scientifically as Φ-structures, and more indirectly, as physical substrates of consciousness. Identifying and understanding the latter would be the typical target of standard neuroscientific research on consciousness, e.g., finding the brain network minimally sufficient to support consciousness. However, according to IIT, the way a neural substrate exists for itself, as a subjective consciousness, is far better conveyed scientifically by the theory’s notion of Φ-structure and its causal properties. In other words, a PSC truly exists, intrinsically, as a Φ-structure, which means as a conscious entity with such and such phenomenal structure. Thus, the terms “conscious experience” and “Φ-structure” are two ways to describe how a conscious entity exists for itself: phenomenologically in the case of the former; physically/scientifically in the case of the latter. On the other hand, IIT’s eliminativist aspect asserts that all systems that do not specify maximal system integrated information do not exist as conscious, intrinsic entities, and hence, do not truly exist as entities on their own (mind-independently). The entities that are ontologically eliminated include, presumably, atoms, fMRI scanners, cerebellums, living bodies, and distant galaxies, among many others (i.e., all non-PSCs).
Then, in Section 4 we highlighted the tension that this metaphysical position entails regarding IIT’s own declared realism. After presenting and refuting three potential solutions to this apparent contradiction, we proposed what we regard as the most plausible alternative: understanding IIT’s realism as an assertion of the existence of other experiences beyond one’s own, what we have called a non-solipsistic idealist realism.
