Head to head
Functionalism vs Higher-Order Thought Theory
Functionalism and Rosenthal’s Higher-Order Thought, compared field by field from their entries in the Atlas.
At a glance
- Both belong to the Materialism family in Kuhn's Landscape of Consciousness.
- Both treat consciousness as emergent.
- They give the same kind of answer on meaning and purpose.
- On AI consciousness, Functionalism says “Yes” and Higher-Order Thought Theory says “Possible”.
- On life after death, Functionalism says “Conditional” and Higher-Order Thought Theory says “No”.
- On mind uploading, Functionalism says “Likely” and Higher-Order Thought Theory says “Possible”.
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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.
Higher-Order Thought TheoryDavid Rosenthal holds that a mental state is conscious when its subject has a higher-order thought that he or she is in that state, a thought that need not itself be conscious and does not seem to rest on inference. Mental qualities such as the redness of a sensation exist whether or not they are conscious; Rosenthal explains them separately, by how they map the perceptible properties we can discriminate.
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.
Higher-Order Thought TheoryA state’s being conscious consists in the subject being aware of it by way of a suitable higher-order thought that one is in that state.
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.
Higher-Order Thought TheoryPossibleSince consciousness depends on having suitable higher-order thoughts about one’s own states, a system able to form such thoughts would meet the condition in principle.
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).
Higher-Order Thought TheoryNoConscious states are natural states of an organism, so nothing remains conscious once those states stop occurring.
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.
Higher-Order Thought TheoryPossibleIf the relevant first-order states and higher-order thoughts were reproduced, the view gives no principled reason the copy would lack consciousness.
Does it give life meaning?Both agree
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.
Higher-Order Thought TheoryHumanistic onlyThe theory is a naturalistic account of mental states and carries no cosmic purpose.
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.
Higher-Order Thought TheoryPhysicalism (naturalistic functionalism)
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'.
Higher-Order Thought TheoryMental states, their qualities, and the higher-order thoughts that make them conscious are all natural states of the organism; Rosenthal expects neural correlates of consciousness to be whatever mechanism produces the higher-order awareness.
Fundamental or emergent
FunctionalismEmergent. Consciousness arises from the functional organization realized by a sufficiently complex substrate (like neural tissue or computer chips).
Higher-Order Thought TheoryEmergent
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.
Higher-Order Thought TheoryMental qualities are fixed by their role in perceptual discrimination and occupy a ‘quality space’ that mirrors the similarities among perceptible properties. Because these qualities do not depend on consciousness, a sensation can have qualitative character without being conscious, as in subliminal perception.
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.
Higher-Order Thought TheoryA non-inferential higher-order thought that one is in a given state, which makes that first-order state conscious even when the thought itself is unconscious.
Where it is
FunctionalismDistributed wherever the functional organization is successfully realized, regardless of whether the substrate is neural tissue or hardwired computing components.
Higher-Order Thought TheoryNot stated
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).
Higher-Order Thought TheoryNot stated
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.
Higher-Order Thought TheoryConceptually testable
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.
Higher-Order Thought TheoryNot stated
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.
Higher-Order Thought TheoryFirst-order theorists argue that higher-order awareness is an unneeded extra ingredient, and deflationists say being aware of a conscious state is like ‘smiling a smile’. Rosenthal replies that a deflated awareness cannot explain the contrast between conscious and unconscious states.
Sources
Key sources
Functionalism
- What is functionalism? (N. Block) (1980)
- What Is Functionalism? Consciousness, Function, and Representation (N. Block) (2007)
- Functionalism (J. Levin) (2023)
Higher-Order Thought Theory
- Rosenthal’s Higher-Order Thought, Landscape of Consciousness, David Rosenthal (2005)