Introduction
Integrated information theory claims to start from experience itself. That claim can be checked. This reading models how to assess a theory's description of experience phenomenologically, using one of IIT's axioms as the case. It works through four steps, flags a common pitfall, and ends with an annotated evaluation table for the axiom. This content reflects the field as of September 2026.
Locating the Theory
The current statement of the theory is "Integrated Information Theory (IIT) 4.0" (Albantakis et al. 2023). It's open access, so you can read along. The axioms are set out near the start of the paper, before the postulates and the mathematics, which this reading doesn't need.
IIT 4.0 begins with a zeroth axiom and five further axioms, which it calls the essential properties of experience. Here they are, paraphrased, with short key phrases quoted.
| Axiom | IIT 4.0's claim about every experience |
|---|
| Existence | Experience exists: there is something. |
| Intrinsicality | Experience "exists for itself," not relative to an outside observer. |
| Information | Experience is specific: it is "this one," not another. |
| Integration | Experience is unitary: "a whole," irreducible to separate experiences. |
| Exclusion | Experience is definite: it is "this whole," with determinate borders. |
| Composition | Experience is structured: composed of distinctions and the relations that bind them. |
The theory claims these properties are immediate and irrefutably true of any conceivable experience. From each, it derives a postulate about what a physical substrate must be like.
Walking Through the Check
Step 1: Take one axiom and state the phenomenological claim it makes
Choose one axiom and restate it as a claim about experience, in plain terms. Take integration. The claim is that at any moment, your experience is one experience, not a collection of separate ones. When you see a blue book on a table, you don't have one experience of blue, another of the book's shape, and a third of the table. You have a single experience that includes all of them.
Stated this way, the claim can be checked by attending to experience.
Step 2: Test it against a described experience
Now test the claim against a case. The unity of a visual scene is the standard one. Look around the room you're in. The objects appear together, in one field, related to each other in space. It would be strange to describe this as several experiences that happen to occur at once.
Extend the case across the senses. As you read, you may hear traffic and feel the chair. These seem unified too. So far, the axiom fits.
Then look for hard cases. Bayne points to cases of brain damage in which a person can see the parts of an object but can't see them as one thing (Bayne 2018). The case doesn't refute the axiom, but it shows that "unified" needs specifying. Unity of the whole field and unity of each object's features are different claims.
Step 3: Check whether the axiom captures temporal flow, horizon, embodiment, and self-givenness
Next, check the axiom against structures phenomenologists have described.
- Temporal flow. Your experience of a sentence holds the words just read and anticipates the next. The axiom speaks of experience as a whole, but its formulation doesn't say whether the whole extends in time. It's silent on the flow.
- Horizon. The book's unseen back and the room beyond your view are part of how the scene is given, though not directly seen. It's unclear whether the "whole" includes these implicit elements or only what's explicitly present.
- Embodiment. Your scene is given from a body, oriented around where you are and what you can do. The axiom doesn't mention this.
- Self-givenness. Your experience is given as yours. IIT's intrinsicality axiom, that experience exists for itself, sounds close. But existing for itself, not relative to an observer, isn't the same as being given as mine. The resemblance needs checking, not assuming.
The shift here is from asking whether the axiom is true to asking whether it's complete.
Step 4: Judge whether the axiom is a description or a theoretical posit
Finally, ask what kind of claim the axiom is. Bayne argues that IIT's axioms face a dilemma (Bayne 2018). Read weakly, an axiom may be self-evident but constrain nothing. Read strongly, it constrains the theory but isn't self-evident.
Apply this to integration. "Experience is unitary" is close to a description: you can check it by attending. "Irreducible to separate experiences" goes further, and irreducibility is what the theory later measures in causal terms. If you can't find irreducibility in experience, only infer it, part of the axiom is a posit dressed as a description.
Key Considerations
Terms.
| Term | Meaning in this check |
|---|
| Axiom | A claimed essential property of every experience |
| Postulate | IIT's corresponding requirement on a physical substrate |
| Description | A claim you can check by attending to experience |
| Theoretical posit | A claim adopted for its role in a theory, not found in experience |
| Horizon | The implicit context co-given with what's explicitly perceived |
A common pitfall. The most common pitfall is rejecting a theory because of its metaphysics instead of evaluating its description.
- IIT has implications many find implausible, such as that some very simple systems have some consciousness. That's a separate question from whether its axioms describe experience well.
- A phenomenological check targets the starting description. It asks whether the explanandum is accurate and complete.
- A good description can support a theory you reject. If the integration axiom fits experience, that counts in the theory's favor on that point, whatever you think of its identity claim.
Summary
The walkthrough restates one axiom as a phenomenological claim, tests it against described experience, checks it against temporal flow, horizon, embodiment, and self-givenness, and judges how much of it is description and how much is posit. Here is an annotated evaluation table for the integration axiom to check your work against:
| Check | Finding for the integration axiom |
|---|
| Phenomenological claim | At any moment, experience is one experience, not several[1] |
| Test case: visual scene | Fits: objects appear together in one field |
| Hard case: seeing parts but not wholes | "Unified" needs specifying: field unity or object unity?[2] |
| Temporal flow | Not addressed |
| Horizon | Unclear whether the implicit is part of the whole |
| Embodiment | Not addressed |
| Self-givenness | Not addressed by this axiom; intrinsicality is related but distinct[3] |
| Description or posit | "Unitary" is descriptive; "irreducible" may be a posit[4] |
- Restating the axiom turns it into a claim you can check by attending.
- Bayne's hard case doesn't refute the axiom. It shows that the axiom's claim is ambiguous.
- Resemblance isn't identity. Existing for itself and being given as mine are different properties.
- The dilemma. The descriptive part is checkable. The irreducibility claim anticipates the theory's causal measure, which is where Bayne's dilemma applies.
References
- Albantakis, Larissa, Leonardo Barbosa, Graham Findlay, Matteo Grasso, Andrew M. Haun, William Marshall, William G. P. Mayner, et al. 2023. "Integrated Information Theory (IIT) 4.0: Formulating the Properties of Phenomenal Existence in Physical Terms." PLOS Computational Biology 19 (10): e1011465.
- Bayne, Tim. 2018. "On the Axiomatic Foundations of the Integrated Information Theory of Consciousness." Neuroscience of Consciousness 2018 (1): niy007.