I began with microtubules.
I was watching a discussion about whether the tiny structural tubes inside cells might be doing more than holding neurons together. Perhaps, the argument went, they support unusual electromagnetic or quantum states. Perhaps experiments involving MRI or NMR have detected signs of coherence or entanglement across unexpectedly large regions. Perhaps consciousness depends on physical organisation at a much finer scale than ordinary neuroscience has been looking.
I wanted to know what all this meant. What were the alleged photon states? What exactly had the experiments found? What did “macroscopic quantum entanglement” mean in this context?
But a more awkward question kept appearing underneath the scientific ones.
Suppose the whole line of inquiry succeeds.
Suppose microtubules really do sustain some previously unknown quantum process. Suppose that process coordinates activity across the brain. Suppose we can interrupt it and consciousness disappears, restore it and consciousness returns, alter it and the character of experience changes in precise and predictable ways.
Would that explain consciousness?
It would be an extraordinary discovery. It might completely revise our account of how consciousness is produced. But it would still seem to leave untouched the question I was actually trying to ask:
Why does one physical state feel like pain rather than red?
Why does another feel pleasant?
Why does either feel like anything?
And why do the physical description and the subjective description concern the same reality?
The more closely I looked, the more it seemed that I had encountered more than a gap in our current science. I had encountered a gap between two different kinds of question.
A mechanism is not yet an answer to what something is
Many mechanistic explanations tell us how one state produces another. Science can also explain by identifying, unifying, revealing structure or showing what something is made of. But mechanism was the kind of answer the microtubule proposal appeared to offer.
Damage activates these receptors. Signals travel along these pathways. Particular networks become active. Attention narrows. Memory is updated. The organism withdraws, reports pain and learns to avoid the source.
That is not trivial. It explains an enormous amount about pain: what causes it, what it does, why it evolved, how it changes behaviour and how it might be prevented.
But every step is stated in intersubjectively testable, third-person terms. Even if the account became complete down to the last molecule, it would still describe a sequence of physical events and functional consequences. It would not by itself tell us why that sequence is present to itself as this particular hurt.
The same problem survives any change in scale. Neurons may be too coarse. Perhaps the important events happen in microtubules, electromagnetic fields, quantum states or some physical process we have not yet imagined. But greater resolution does not by itself change the kind of answer being given.
If I ask what a film is about, a more powerful microscope aimed at the screen will not answer me. It will show me the pixels with astonishing precision. It may explain exactly how the image is produced. That is real knowledge. It is simply knowledge of a different relation.
This analogy does not prove that meaning is separate from the organised pixels. It makes a narrower point: increasing resolution does not automatically answer a question pitched at a different explanatory level.
That was the first turn in the argument. Perhaps the problem is not that our mechanism is insufficiently fine-grained. Perhaps mechanism, however fine-grained, answers a different question.
So what would count as an answer?
That sounds like an easy objection to make and a difficult one to satisfy. If a causal account alone would not be enough, what exactly am I asking science or philosophy to provide?
At first, the answer seemed to be a bridge.
An answer to my question, I thought, would need to do more than correlate brain states with experiences. It would have to show why a particular physical organisation necessarily gives rise to a particular felt quality. It would explain why this state is pain and not red, why that state is pleasant rather than neutral, and why some physical processes are accompanied by experience while others apparently are not.
It would connect the two descriptions so tightly that the subjective fact could be derived from the physical one.
This is a much stronger standard than correlation. A table saying:
Physical state P occurs whenever experience E occurs.
is not yet the kind of explanation I was seeking. Nor is a perfectly reliable prediction that whenever P appears, E will follow. Prediction tells us that the relationship holds. It does not tell us what makes it hold.
So perhaps we need a psychophysical law — a bridge principle connecting physical structure to felt experience.
But then the same problem reappears one level higher.
Why does that bridge principle hold?
If the answer is another law, we can ask why that law holds. If the answer is a deeper structure, we can ask why that structure has experiential consequences.
If the theory instead says that P and E are not two things but one thing described from different perspectives, the question changes. What warrants the identity claim? Does it close the intelligibility gap or merely rename it? A genuine identity leaves no relation of accompaniment requiring a further cause. But an epistemic problem can remain: why do the physical and phenomenal concepts present their supposed common referent so differently?
If it remains a bridge rather than an identity, the bridge may be exact, elegant and perfectly predictive. But unless it does something more, it remains a description of the relationship.
We have drawn a flawless map of the crossing. We have not explained why there is a crossing at all.
From mechanism to identity
The obvious next move is to say that consciousness is not produced by the physical state. It is the physical state.
Pain just is a certain organised process, encountered from the inside. The neural or quantum description and the felt description pick out the same event in different vocabularies.
This is more than a mechanism. It is an ontological claim: a claim about what consciousness is.
It may even be true.
That need not be a defect. Genuine identities often explain by revealing that two apparently different things are one. But an asserted identity has to be earned. In the consciousness case it also owes us some account of why the two modes of access seem so radically unlike one another.
Once earned, an identity can end an ontological regress: there are no longer two things whose connection needs a cause. Yet it becomes a terminus in our account rather than a derivation of experience from wholly non-experiential terms. At some point, the identity is accepted as fundamental or placed inside a larger framework.
Other finite theories locate the bedrock elsewhere.
Dualism says experience is a different kind of property linked to matter by fundamental laws. Then those laws are where explanation stops.
Panpsychism says experience, or something proto-experiential, is already a basic feature of reality. Then experience is part of the starting furniture. Some versions shift the difficulty to how local experiential aspects could compose a unified mind.
Idealism says experience is fundamental and the physical world is a stable structure within it. Then matter no longer has to generate consciousness, but we must explain why experience takes the regular, apparently external form that physics describes.
Functionalism identifies consciousness with what a system does — the organisation of discrimination, integration, memory, attention and control. Then the question becomes whether a complete account of those roles includes felt presence or has defined the original difficulty out of view.
These theories are not therefore equivalent, and they are not equally well supported. Some may explain far more than others. But when offered as finite, foundational accounts, they eventually reach a point at which something is no longer explained in terms of something deeper. It is identified, postulated or treated as fundamental.
That is when the problem of consciousness opened into a larger problem about explanation itself.
Every explanation spends something it does not explain
An explanation often has the form:
This is the case because of that.
The unfamiliar is made intelligible by placing it inside a structure we already accept. The falling object is explained by gravity. The organism’s trait is explained by selection. The market crash is explained by interacting incentives, expectations and feedback loops.
If we renew the demand for explanation at every level, some part of the explaining structure must temporarily be allowed to stand.
Why gravity? We can answer with general relativity. Why that geometry? We can answer with a deeper physical theory, if we find one. Why that theory, those laws, that mathematical structure, that existence rather than another?
Each answer buys understanding by borrowing from somewhere else. It reduces one mystery by placing it inside another framework. We may have very good reasons to regard the new framework as deeper, wider or more powerful. But the demand for a reason can be applied again.
That does not mean every new “why?” is coherent. Part of explaining well is knowing when the relevant contrast has disappeared or the question has lost its grip. But if we insist in advance that no premise may remain ungrounded, the demand keeps renewing itself.
This does not mean that all explanations are worthless. A theory that unifies thousands of observations, makes risky predictions and reveals hidden structure is immeasurably better than saying “it just happens.” Explanation has depth, reach and quality.
By ultimate explanation here, I mean that unusually severe demand: every discursive reason must receive a further reason, no premise may remain ungrounded and nothing is allowed to stand simply because the explanatory purpose has been met.
It is not clear that such an account is possible.
There may be a bottom in being. Reality may have an irreducible structure. But there may be no bottom in reasons — because the moment we describe the bottom, the mind can ask why reality has that structure rather than another.
And eventually there are only four places to go.
The four endings
These are not four possible scientific theories, nor four structures of exactly the same kind. The first three are the possible shapes of an indefinitely renewed chain of discursive reasons: it continues, bends back or stops. The fourth is the other possible response — to relinquish or transform the demand for another link. Together they are the four ways the demand, as I had framed it, can end.
1. The chain continues forever
Every fact is explained by a deeper fact, every law by a deeper law, every framework by a more general framework.
There is no last explanation. There is only indefinite progress.
This preserves the demand that every answer must have a reason, but it never supplies an answer that is complete. Reality becomes an endless depth from which local understanding can always be extracted but which can never be finally grounded.
2. The chain bends back
The parts explain one another within a mutually supporting whole.
Our account of mind depends on our account of matter; our account of matter depends on the observations and concepts available to mind. Meaning depends on use; use depends on a community; the community depends on shared meanings.
This need not be a crude logical circle. It can be a coherent web in which no single proposition is the foundation and the strength lies in the fit of the whole. This is clearest as a theory of justification or mutual intelligibility, not necessarily of cause. But the whole does not receive a further reason from outside itself.
3. The chain stops
Something terminates the demand.
A law, an identity, a substance, a structure, a field of experience, a divine nature, a bare fact: at some point the answer becomes, “This is simply how reality is.” Or it claims something stronger: that the terminus is necessary or self-explanatory and could not coherently have been otherwise.
Every finite foundational worldview has such a point, whether or not it admits it. Physicalism may stop at physical law or identity. Dualism may stop at the relation between mind and matter. Panpsychism may stop at experience as fundamental. Idealism may stop at the nature of mind.
Calling the stopping point “fundamental” does not derive it from anything deeper. Calling it “necessary” may be more illuminating than accepting a brute fact, but then the argument moves to whether that necessity belongs to reality or only to our concepts. Either way, the renewed demand has reached a proposed terminus.
4. The demand is relinquished or transformed
We may decide that another reason is no longer what is needed. The question may rest on a false contrast, commit a category error, or have already been answered well enough for its purpose. In the case of consciousness, the transformation can take a more distinctive form: instead of trying to know experience only by placing it beneath another description, we also recognise the way it is known directly.
Consciousness is unusual because this is already how it is given. I do not infer that experience exists from a measurement or a theory. Experience is present before inference. Whatever else I may doubt, the appearing itself is not reached by explanation; it is the condition in which explanations appear.
This fourth response does not complete the chain of reasons. It declines the demand for another link, or changes the mode of inquiry. It says that description is not the only form of knowing, and that some realities may be known most fundamentally by participation, presence or direct acquaintance.
That can sound mystical, but the basic point is ordinary. An explanation does not have to instantiate what it explains: a chemical analysis of sweetness need not itself become sweet. The narrower point is that possessing the analysis does not confer acquaintance with sweetness. Someone could know the description without having tasted it. Description can explain conditions, relations and effects with extraordinary precision without becoming presentation.
So the first three exhaust the possible shapes of the recursively renewed chain. The fourth questions whether the answer we seek must be another link in it.
Why consciousness makes the limit impossible to ignore
In most fields, we can forget this problem.
We do not need an ultimate account of why there is something rather than nothing in order to build a bridge. We do not need to ground the laws of logic before diagnosing an infection. Local explanations can be complete for their purpose even if the deepest framework remains unexplained.
Consciousness is different because the thing to be explained is also the place from which explanation happens.
Scientific inquiry represents phenomena in intersubjectively testable terms: measurable properties, relations and causes. This is its power. First-person reports can be included as evidence, but the report available to another observer is still a representation of the experience, not a transfer of what it is like.
The method may discover every condition under which experience changes. It may reveal the mechanisms of wakefulness, attention, memory, report, selfhood, anaesthesia, hallucination and pain. It may find that microtubules matter enormously, or not at all. None of this work is diminished by the philosophical problem.
This can leave intact the gap it is being asked to close. The account captures what can be shared and tested, then asks how the somewhere it is like to be fits into that account.
Perhaps no accumulation of third-person detail can, without some further bridge premise, entail or convey first-person presentation. Detail may not be what separates the two. They may be different modes of access to whatever the underlying reality is.
If so, the question “Why does this feel like pain rather than red?” may contain several questions tangled together.
One is empirical: what structures distinguish pain from colour perception?
One is functional: why do those states affect attention, memory and behaviour differently?
One is evolutionary: why did organisms develop those discriminations?
One is ontological: what is a felt quality, and how is it related to the physical process?
And one is a demand for presence itself to be derived from a description.
The first three are tractable scientific questions. The fourth is where metaphysical theories compete. The fifth may be asking one mode of knowing to transform into another.
What would count as an answer now?
The question had moved from mechanism, to a bridge, to identity, and finally to the conditions I had built into the word answer. The problem was no longer simply that consciousness had not been explained. It was that I could not say what an ultimate explanation would look like without either exempting something from the demand for explanation or refusing the demand itself.
That was the progress the question forced.
It does not show that neuroscience is irrelevant, that consciousness is supernatural or that every theory is as good as every other. It shows only that a complete causal account and an ultimate account of what something is are not automatically the same achievement.
We should continue looking for the mechanisms. They may transform medicine, philosophy and our picture of nature. They may show that our current categories of mind and matter are badly drawn. A sufficiently deep theory might even dissolve much of the apparent gap.
But if we ask it for a final reason why reality includes felt presence at all, we should notice what we are demanding. For the demand as I had framed it — every reason must itself receive a reason — four responses remained: let the chain continue, let it bend back, let it reach a terminus, or relinquish and transform the demand. In the consciousness case, that fourth response may include the passage from description to direct acquaintance.
A more powerful microscope could radically alter the causal or constitutive account. Greater resolution alone cannot decide which response to the ultimate demand is legitimate.
I began with the tubes inside a neuron. I ended at the edge of explanation.
Perhaps consciousness is not where science fails. Perhaps it is where the structure of explanation becomes visible.
Perhaps we are not waiting for a fifth option. We are trying to see which of the four forms our answer takes — and whether the demand that led us there deserves to survive.
This essay began with a Closer To Truth discussion with Mike Wiest about microtubules and consciousness.