Head to head
Functionalism vs Integrated Information Theory
Functionalism and Integrated Information Theory (IIT), compared field by field from their entries in the Atlas.
At a glance
- Functionalism belongs to the Materialism family in Kuhn's Landscape of Consciousness, Integrated Information Theory to Information.
- On AI consciousness, Functionalism says “Yes” and Integrated Information Theory says “No”.
- On life after death, Functionalism says “Conditional” and Integrated Information Theory says “Uncertain”.
- On mind uploading, Functionalism says “Likely” and Integrated Information Theory says “No”.
- On meaning and purpose, Functionalism says “Humanistic only” and Integrated Information Theory says “Uncertain”.
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The claim
In brief
FunctionalismFunctionalism posits that mental states are defined by their causal relations to one another, to sensory inputs, and to behavioral outputs, independent of the physical medium (substrate) in which they are realized. The essence of consciousness is determined by how mental states function or operate, rather than by what they are materially composed of.
Integrated Information TheoryIIT is an original, radical model that proposes a definition for conscious experience and specifies which physical systems can possess it, starting from the phenomenology of consciousness (axioms). It translates these axioms into physical postulates based on intrinsic cause-effect power, featuring a mathematical measure Φ(Phi) to quantify a system's capacity for informational integration, which correlates with the degree of consciousness.
What consciousness is
FunctionalismMental states are identified as functional states, constituted by their causal relations, roles, results, and outputs, implying they are realizable in any substrate that supports those functions.
Integrated Information TheoryConsciousness is identified as a Φ-structure, a maximally reduced conceptual structure existing in 'qualia space'. An experience is identical to this conceptual structure, meaning its phenomenal properties correspond precisely to the physical properties of the cause-effect structure unfolded from the physical substrate of consciousness (PSC).
Big questions
Can AI be conscious?Differ
FunctionalismYesFunctionalism holds that consciousness is based on function, not biology. If the correct functions can be realized computationally in non-biological substrates, AI consciousness is possible in principle and certain if Materialism is true.
Integrated Information TheoryNoKoch, a proponent, argues that consciousness is not computable. Digital computers have negligible integrated information (Φ(Phi)) due to hardware structure, meaning they can never be sentient, regardless of intelligence.
FunctionalismConditionalAs a physicalist theory, consciousness is tied to the substrate. Survival beyond death of the biological body is only possible if the functional mental state can be successfully transferred (uploaded) to a new, continuing substrate (virtual immortality).
Integrated Information TheoryUncertainIf phenomenal consciousness requires a radically new structure (like IIT's postulates), the potential permanence of these 'inscrutable things' cannot be rejected, leaving the possibility of survival open, even though IIT does not explicitly espouse life after death.
FunctionalismLikelyFunctionalism serves as the theoretical basis for virtual immortality. If the functional role of the mental self can be perfectly duplicated and uploaded to a new medium, the first-person mental self is preserved.
Integrated Information TheoryNoIf consciousness is a fundamental property tied to real cause-effect power, a digital simulation (uploading) would only create a 'perfect zombie'—an entity that acts like the original but lacks subjective consciousness—because the simulation is virtual, lacking the required real cause-effect power.
FunctionalismHumanistic onlyFunctionalism describes the mechanism by which mind/consciousness operates within a physical world, providing capacities for agency and reflection, but offers no rationale for ultimate cosmic meaning or teleology, aligning with the general stance of Materialism.
Integrated Information TheoryUncertainWhile the measurement and analysis of consciousness do not convey ultimate meaning, the speculative nature and novelty of the innumerable nth dimensional conceptual structures (conscious percepts) warrants suspending judgment on ultimate meaning/purpose/value.
Nature of mind
Ontology
FunctionalismPhysicalism (broadly, agnostic to substance). The theory is classified under Materialism, but it is metaphysically agnostic regarding nonphysical substances, focusing primarily on the functional description of mental states.
Integrated Information TheoryIIT's fundamental ontology is the ontological primacy of phenomenal existence, based on an intrinsic powers view where what truly exists in physical terms are intrinsic entities capable of cause and effect. Koch notes that the theory insists consciousness must be incorporated into the basic description of reality at the rock-bottom level.
Mind and body
FunctionalismMental states are functional states identical to the functional roles that are realized or instantiated in a physical substrate, leading to 'functional state identity theses'.
Integrated Information TheoryIIT asserts an explanatory identity: an experience is identical to a Φ-structure. It contends that the conscious entity is the Φ-structure expressing its causal powers, not the neural substrate itself. This framework leaves no room for emergence or dualism.
Fundamental or emergent
FunctionalismEmergent. Consciousness arises from the functional organization realized by a sufficiently complex substrate (like neural tissue or computer chips).
Integrated Information TheoryConsciousness is defined by intrinsic existence and characterized as belonging to the basic description of reality. The theory rejects emergence.
Qualia
FunctionalismThe theory traditionally struggles to account for phenomenal qualia, often addressing them by asserting that the qualitative feel is entirely exhausted by the functional role, or by coupling with representational theories.
Integrated Information TheoryDistinct conscious experiences are conceptual structures in a 'qualia space'. The qualitative feel (phenomenal properties) corresponds one-to-one to the physical properties of the maximally irreducible cause-effect structure, which is also called a quale.
How it works
Mechanism
FunctionalismThe principle of multiple realizability, stating that mental state realization is independent of the physical substrate, contingent only upon the required function being instantiated.
Integrated Information TheoryThe core principle is Integrated Information (Φ(Phi)), which quantifies the system's irreducibility. The Exclusion Postulate ensures that only the maximally irreducible cause-effect structure (the Φ-structure) exists intrinsically, defining the boundaries and grain of consciousness.
Where it is
FunctionalismDistributed wherever the functional organization is successfully realized, regardless of whether the substrate is neural tissue or hardwired computing components.
Integrated Information TheoryConsciousness is not limited to biological brains. IIT predicts the conscious structure resides in the posterior cortex (occipital, parietal, and temporal cortices). Systems with maximally irreducible intrinsic cause-effect power possess consciousness.
What it does
FunctionalismFunctions, roles, and outputs are dispositive. Mental states are causally effective because they are defined by their causal relations within the system (functional role).
Integrated Information TheoryConsciousness is identified as unfolded intrinsic causal power, which is the ability to effect change. Only this intrinsic entity (the Φ-structure) can cause, supporting the claim that true free will exists for systems with high Φ(Phi).
Evidence and criticism
Testability
FunctionalismConceptually and empirically testable. Thought experiments (like substrate replacement) probe its conceptual limits, and computational realization (AI) tests its empirical application.
Integrated Information TheoryIIT claims scientific testability, employing quantitative measurement. However, critics argue that the theory is not truly empirically tested, and its core predictions may be idiosyncratic.
Tests so far
FunctionalismThe silicon chip replacement thought experiment is used conceptually to test whether phenomenal consciousness is preserved when the functional role is maintained across a change in substrate.
Integrated Information TheoryCalculating Φ(Phi) for specific neural networks (e.g., visual cortex).,Monitoring brain activity as subjects slip into anesthesia.,Adversarial collaboration experiments testing predictions about sustained activity in the posterior cortex.
Criticisms
FunctionalismIt is criticized heavily for failing to account for phenomenal consciousness (qualia) by describing only the functional role, leading to the 'hard problem' challenge that functional roles may not exhaust the nature of conscious experience.
Integrated Information TheoryThe theory faces criticism for anti-common sense predictions (imputing consciousness to simple objects). A public letter characterized IIT as 'pseudoscience'. Critics challenge that experiments test only idiosyncratic predictions and not the core metaphysical ideas. Chalmers noted the 'pseudoscience' label was disproportionate and caused vast collateral damage.
Sources
Key sources
Functionalism
- What is functionalism? (N. Block) (1980)
- What Is Functionalism? Consciousness, Function, and Representation (N. Block) (2007)
- Functionalism (J. Levin) (2023)
Integrated Information Theory
- From the phenomenology to the mechanisms of consciousness: integrated information theory 3.0, Oizumi, Albantakis, Tononi (2014)
- Consciousness: here, there and everywhere?, Tononi and Koch (2015)
- Only what exists can cause: an intrinsic powers view of free will, Tononi et al. (2022)
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