For years a friend and I argued this question. Add enough lines of code in just the right way, he holds, and you can obtain any possible behavior; accept the computational theory of mind, and write the right program, and any possible conscious experience comes with it.

The condition carries the argument: accept the computational theory of mind. On that view, the right computation suffices for experience. But why accept it? The Church-Turing-Deutsch principle can look like an answer. It leaves the crucial step unproved.

In 1985, David Deutsch proposed a universal quantum computer and stated this principle: “Every finitely realizable physical system can be perfectly simulated by a universal model computing machine operating by finite means.” A suitable computer could reproduce a system’s responses to specified tests, without duplicating its material.¹

The older Church-Turing thesis concerns what a person following a mechanical procedure can calculate. Deutsch’s principle concerns physical systems, including brains. That seems to close the gap between a theory of calculation and a theory of mind.²

Grant the principle.³ The proposed argument runs:

1. A brain produces conscious experience.
2. A universal computer can simulate that brain perfectly.
3. Therefore, running the simulation produces conscious experience.

The missing premise sits between the second step and the third: the simulation preserves whatever makes the brain conscious. Deutsch’s principle does not tell us whether it does.

A calculator program really adds because the machine performs the required operations. A weather program calculates how wind and pressure would change without blowing rain across the room. John Searle used rainstorms and fires to make this distinction in “Minds, Brains, and Programs” (1980). Modeling a process does not automatically give the computer every property of the process modeled.⁴

But the example cannot decide whether consciousness belongs with calculation or rain. Nor can the word simulation. A computer connected to a valve can really control it. Its operations have effects; they need not merely describe effects occurring elsewhere.⁵

David Chalmers thinks the brain simulation belongs with the calculator. In The Conscious Mind, he argues that experience depends on the fine-grained pattern of causal interactions among a system’s parts, rather than the material making them up. He calls this organizational invariance.⁶

Imagine replacing your neurons with artificial components that preserve those interactions. They respond as the neurons would, including to inputs you never actually receive. Memory, attention, judgment, and reasoning continue unchanged.

Now suppose your visual experience fades as the replacements proceed. The tomato’s red drains toward gray, but you still judge that you see the same vivid red. Nothing in your memory or attention registers the loss. Or suppose a switch makes your experience alternate between two colors while every means of noticing the change stays fixed. These are Chalmers’s “fading” and “dancing” qualia cases.⁷

He finds that separation between experience and all cognitive recognition deeply implausible. Preserving the organization, he argues, should preserve the experience. A critic must answer this argument, not merely repeat that silicon simulates neurons.

Chalmers has supplied a reason to accept the missing premise. Its force comes from his account of experience and cognition, not from Deutsch’s principle. The physical principle can contribute to a larger argument; it cannot establish computationalism by itself. Assuming computationalism to fill the gap would beg the question. Defending it independently does not.

The replacement argument nevertheless does not by itself prove what strong computationalism needs. It changes the neural material while leaving the rest of the subject’s body, surroundings, causal history, and continuing commerce with the world in place. The silicon successor still looks at this red tomato, reaches for this cup, and inherits the organism’s established relations to both. If experience survives the substitution, the case supports substrate independence under those preserved conditions. It does not show that the preserved conditions make no constitutive contribution.

Chalmers has a direct reply. In discussing Inverted Earth, he allows that environmental reference and wide belief content can change while the subject’s internal organization and experience remain the same. If phenomenal character is narrow in that way, changing the world will not threaten phenomenal organizational invariance.⁸

My own view rejects that restriction. It includes the world because the world is necessary. Phenomenal character concerns how an experience looks or feels. It consists in representational content of the right kind: what experience presents and how it presents it. Not every difference in wide content makes a phenomenal difference; Oscar and Twin Oscar may experience H₂O and XYZ in exactly the same way. But differences in phenomenally relevant content, including what color an experience presents, make differences in phenomenal character. The relevant organization is therefore wide. It includes the embodied, causal, and historical relations through which perceptual states acquire their content.

Now reconsider the dancing-qualia wedge. Chalmers asks us to imagine experience changing while the subject’s judgments, memories, and dispositions remain fixed. The wider alternative can preserve the internal vehicles, causal roles, and dispositions to judge while the world-involving contents of experience, judgment, and memory vary together. No mismatch opens between what the subject experiences and what the subject thinks. This does not refute Chalmers from neutral ground; it identifies the disputed premise. His replacement sequence assumes narrow phenomenal individuation when it holds the world fixed. It cannot then establish that assumption.

On the wider account, neural replacement preserves experience not because the same abstract internal program must carry the same phenomenology wherever it runs, but because the organism’s complete world-involving organization has been preserved.

The computationalist now faces a dilemma. If “organization” means narrow internal causal topology, the replacement arguments do not establish organizational invariance. If it includes the necessary relations among brain, body, history, and world, organizational invariance may hold, but it no longer supports the claim that implementing the right internally specified program suffices for mentality. The same program can be copied while those relations differ or fail to exist.

It also leaves room for artificial minds. A copied brain may inherit a history; going offline does not erase it. Training can give a system content about real features of the world, including language.⁹ Virtual objects can enter genuine causal relations with an agent that learns from its mistakes. A computational account that includes those relations deserves a hearing.

We would still need to examine the running system: how its perceptions guide memory and action, how corrections endure, and whether those activities belong to one continuing subject. A formal description alone leaves those questions open. Saying that a simulation is “perfect” does not answer them.

That closes the route from the Church-Turing-Deutsch principle to strong computationalism. Deutsch shows that physical evolution can be simulated. Chalmers’s cases may show that biological material is not uniquely necessary when the wider organization is preserved. Neither shows that computation by itself constitutes thought or experience. A computer may still think or experience, but only as a concrete system whose embodied and world-involving relations do constitutive work as well. We must establish that those relations exist and explain how they make the process intentional or conscious. We cannot read that answer off the program or borrow it from universal simulability.

-gts

---

This essay is part of Mind, Matter, and Meaning, an AI-assisted philosophy project by Gordon Swobe exploring consciousness, meaning, and artificial minds. Learn more about the project and read the book.

---

Notes

1. David Deutsch, “Quantum Theory, the Church–Turing Principle and the Universal Quantum Computer,” Proceedings of the Royal Society of London A 400 (1985): 97–117, at 98–99. Deutsch defines simulation through computational equivalence under input/output labelings, with equivalent preparations and measurements yielding statistically indistinguishable output distributions. This operational criterion should not be conflated with material duplication, efficient simulation, or an available engineering procedure. His discussion of quantum theory’s compatibility with the principle does not constitute an unrestricted proof of physical universality. The universal quantum computer also does not thereby compute nonrecursive functions. The present argument grants the physical principle rather than deriving it from the mathematical Church-Turing thesis. ↩
2. Gualtiero Piccinini, “Computationalism, the Church–Turing Thesis, and the Church–Turing Fallacy,” Synthese 154 (2007): 97–120, https://doi.org/10.1007/s11229-005-0194-z. Piccinini explicitly credits Jack Copeland for the fallacy’s name. His distinction separates the generic claim that cognitive processes compute from the technical claim that a computation falls within Turing-computability. Establishing the latter does not establish the former. His conclusion treats computationalism as an empirical hypothesis about cognitive organization, not a consequence of results concerning effective calculability. The present essay addresses the further phenomenal conclusion: even a warranted computational explanation of some cognitive capacities would require an account of why its realization suffices for experience. ↩
3. Christopher G. Timpson, “Quantum Computers: The Church-Turing Hypothesis Versus the Turing Principle,” in Alan Turing: Life and Legacy of a Great Thinker, edited by Christof Teuscher (Berlin: Springer, 2004). The argument also appears in chapter 6 of Timpson’s DPhil thesis, Quantum Information Theory and the Foundations of Quantum Mechanics (University of Oxford, 2004), arXiv:quant-ph/0412063. Timpson disputes Deutsch’s proposed underwriting of the mathematical hypothesis by a physical principle, distinguishing effective calculability from physical simulability. This criticism neither establishes nor refutes physical CTD merely by separating the claims. Granting CTD here isolates the inference to mentality; it does not certify the physics or treat the mathematical and physical theses as interchangeable. ↩
4. John R. Searle, “Minds, Brains, and Programs,” Behavioral and Brain Sciences 3, no. 3 (1980): 417–424. The fire-and-rain example establishes that preservation of a computational description does not automatically preserve every property of the described process. Its application to consciousness requires an additional account of consciousness-relevant causal powers. The example therefore supplies neither a general prohibition on realization through simulation nor a classification of consciousness with combustion or precipitation. Its limited inferential role does not depend on accepting the Chinese Room argument advanced in the same paper. ↩
5. Shuqin Ma and Ryota Kanai, “Intrinsic Computational Functionalism: From Observer-Relative Maps to Observer-Independent Structures,” arXiv:2606.06424v1 (2026), secs. 3–5, propose label-independent instantiation and intervention-sensitive causal-dynamical organization as constraints on intrinsic computation. These constraints address unconstrained observer-relative mappings without selecting the structures sufficient for consciousness. Ryota Kanai and Shuqin Ma, “Intrinsic Computational Functionalism and Simulated Consciousness,” arXiv:2606.15348v1 (2026), develop a conditional preservation argument encompassing physical implementation, state individuation, transitions, intervention profiles, and the relevant agent-body-world boundary. If consciousness is invariant under that organization and an implementation realizes it, consciousness is preserved. This is stronger than a narrow input/output argument and does not claim that every simulation, or any particular current system, meets the conditions. A criticism must identify a relevant omission rather than infer one from the designation “simulation.” ↩
6. David J. Chalmers, The Conscious Mind: In Search of a Fundamental Theory (New York: Oxford University Press, 1996), 328; the defense of phenomenal organizational invariance appears in chapter 7. The relevant organization includes fine-grained causal dependence and counterfactual response, not merely an actual sequence of outputs. Chalmers’s combination of organizational invariance with property dualism illustrates the distinction between computational sufficiency and physicalist reduction. A principle relating experience to organization could, on his account, hold as a psychophysical law without identifying experience with organization. ↩
7. Chalmers, The Conscious Mind, chapter 7; and “A Computational Foundation,” sec. 3.2. Fading qualia concern progressive experiential loss under organizational preservation; dancing qualia sharpen the challenge through switching between functionally equivalent implementations allegedly associated with different experiences. Cognitive noticing must involve a functional difference, so the stipulated organizational equivalence excludes it. The argumentative pressure comes from the implausibility of radical experiential change without corresponding cognitive recognition. This is not a deductive contradiction unless further premises exclude such dissociation. Chalmers presents the arguments as plausibility arguments about consciousness and cognition. Rejecting them requires addressing that pressure rather than merely redescribing silicon as a simulation. ↩
8. Chalmers, “A Computational Foundation,” sec. 3.2, expressly excludes knowledge and environmentally individuated belief from unrestricted organizational invariance while defending phenomenal invariance. He also considers Inverted Earth in The Conscious Mind, pp. 265–274. The present reply does not infer a phenomenal difference from every difference in wide content. It makes a methodological point about the scope of the replacement cases: varying substrate while retaining the subject’s environment and ongoing causal relations cannot establish invariance across changes in those relations. The additional identity thesis stated in the body—that phenomenal character is representational content under the relevant perceptual or bodily-affective mode—explains why the fixed background belongs inside the relevant organization. It still requires an account of which content differences bear on phenomenal character. An externalist argument concerning belief alone establishes neither a phenomenal difference nor the absence of consciousness. ↩
9. Fintan Mallory, “Teleosemantics for Neural Word Embeddings,” Mind & Language (2026), https://doi.org/10.1111/mila.70037, develops a consumer-based account of word2vec representations concerning the linguistic contexts in which words occur. Linguistic distributions are features of the world; their representation should not be dismissed through an all-or-nothing demand for reference to ordinary physical objects. This supports a serious mechanism-level content attribution without establishing whole-model understanding or a conscious subject. Whether content is original at this limited grain remains unsettled here. The relevant diagnostic asks whether causal-functional history and current producer-consumer use fix accuracy conditions not exhausted by an interpreting practice. Engineered ancestry, inherited vocabulary, or the source of a training objective does not independently settle that question. Derived content also remains genuine content. Similarly, copying and disconnection require an investigation of preserved causal-historical relations rather than an automatic verdict of semantic deprivation. ↩

Get new essays by email