I am quoting here something from George Stuart Fullerton's An Introduction To Philosophy. Here, he is toying with the argument made by W.K. Clifford.

We must assume that consciousness is a complex of elementary feelings, "or rather of those remoter elements which cannot even be felt, but of which the simplest feeling is built up". We must assume that such elementary facts go along with the action of every organism, however simple; but we must assume also that it is only when the organism has reached a certain complexity of nervous structure that the complex of psychic facts reaches the degree of complication that we call consciousness.

I have several problems with this. To begin with, it is assumed that a higher degree of complication brings about consciousness. Without trying to sound blithe towards some of the ground rules of both Philosophy and Science, I say that his statements, to some extent, try to quantify consciousness.

Which is to say that his statements try to make us believe that a certain complexity of nervous structure breathes consciousness into us.

Was the single-cell organism that we evolved from any less self-aware of itself than we are? Amoebas are pretty simple, but as this study suggests, one could argue that they are just as conscious as humans, without requiring the kind of mechanical complexity of machinery that we have.

  • There's nowhere in this study any mention of self-awareness and only "intelligence" not not anything like human intelligence.
    – Mithoron
    Sep 27, 2015 at 16:58

4 Answers 4


Indeed, there is a recent ansatz from neuroscience to quantify the degree of consciousness of an information processing system. Consciousness is considered the excess of information provided by the whole system above the sum of information provided by its separate parts. For short: Consciousness is integrated information.

This approach of mathematization makes it possible to develop a first formal model of consciousness. One can ask what this model achieves, and on the other hand where its limits are. Most of all, the model allows to discuss and to decide questions about consciousness by the methods of science.

By the way, an amoeba does not have consciousness because it does not have neither neurons nor neuronal processes.


Note. The quote does not speak about complication but about complexity.

  • 1
    I agree. If we are ever going to understand the limits of a mathematical/computational model of the mind, then mathematical methods offer the best way forward. The idea of equating subjective experience to excess information sounds intuitively appealing as a statement of "emergence from complexity". It's the first I've heard of it, and I'm hooked. You might consider adding a bit to your answer by indicating how it's possible that the information content of the whole can be measured as greater than the information content of the sum of its parts. Maybe that's not an easy question to answer.
    – nwr
    Sep 28, 2015 at 2:31
  • @Nick R Yes, I consider Tononi's approach a stunning ansatz. The approach uses the concept of entropy which is a standard measure to define the information content of a system state. A relative version of entropy allows to compare the information content of the whole system with the sum of the information of all its parts. Tononi’s paper is free for download from biolbull.org/content/215/3/216.full
    – Jo Wehler
    Sep 28, 2015 at 2:53
  • Thanks. I'll have a look. It looks very interesting. Apparently he is suggesting we use a measure of the probability distributions generated by the respective systems, the difference being the excess. I'll have read and hopefully understand more than ten percent of it.
    – nwr
    Sep 28, 2015 at 3:05
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    Yes, looks like an interesting paper, Carnap redux? My understanding is that such approaches, using Shannon entropy, tend to founder on the issues of some atomic "qualia" and "meaning," as well as self-reporting, memory, and necessary "forgetting." I think these attempts are interesting, but I am always deeply skeptical. I tend to include "gendered embodiment" as basic, so real "consciousness" must also physically reproduce and recognize "itself." Thanks for link. Sep 28, 2015 at 14:18
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    @Nelson Alexander Because you seem to be interested in a critical review of Tononi's paper from a philosophical viewpoint, I would like to draw your attention to Peressini, Anthony: Consciousness as Integrated Information. A Provisonal Philosophical Critique. Journal of Consciousness Studies, Vol. 20, 2013
    – Jo Wehler
    Sep 28, 2015 at 18:47

You're right in being skeptical about all the "we must"s. It does seem, given how profoundly physical interventions can impact consciousness, that it is somehow physically implemented. And, therefore, it must be built out of something. But that does not mean that it's built out of elementary feelings.

As an analogy, take a limit cycle. This is a mathematical phenomenon where a time-varying process takes the same path repeatedly where various parameters change over time, but cyclically. If you perturb the system away from that limit cycle, it will be restored back. If consciousness was anything like this, it wouldn't be built out of "elementary feelings" any more than a limit cycle is built out of stationary attractors.

So to be honest, we must at least admit that we don't know for certain. We then may wish to entertain some educated guesses, and we may wish to consider what the minimal substrate would be for something that is sufficiently akin to what we experience as consciousness to deserve the same label. It does seem that some non-trivial machinery must be there to have not just a response to a perception but some secondary qualia associated with it. That it is like something seems to require both some memory and some pattern-matching capability or else the very notion of like cannot even make sense.

So it seems very likely that there is some minimal complexity below which consciousness, as we understand the term, does not exist.

However, you are wrong in suggesting that an amoeba could plausibly be as conscious as we are. An amoeba probably does not meet the minimal complexity required for consciousness, as it's doubtful that it has the requisite pattern-matching and memory capability. Furthermore, though it is not necessary that consciousness cause or regulate anything, one does at least suspect that if it were there, evolution would favor those organisms that tapped into that computation to modify behavior in ways that enhance survival. Thus we are justified in doubting (though not in concluding for certain) that animals like Dictyostelium and C. elegans have consciousness. They simply do not behave in ways that are consistent with the kinds of capabilities that consciousness might add. (In particular, again, there is no obvious pattern matching.) Drosophila, however, do seem to have all the minimally requisite bits, so I think we should be more open-minded about whether they might have something like consciousness. (Personally I rather doubt it, but this is just a hunch based on how abstracted consciousness seems to me to be, and a further hunch about the effective depth of the fly's neural networks.)

Anyway, it's a difficult topic, and one where, sadly, people too often try to sweep all sorts of important and difficult concerns under the rug in order to try to make progress. I don't think this is progress--not on consciousness anyway--but rather misdirection (even if well-intentioned). I think that's what's going on in this case.

  • I hope that you'll agree with me that this line of minimal complexity that you suggest is almost impossible to delineate. And that in time, with sufficient proof, we might find that something can only be conscious or not conscious, with no in-between. In regard to amoeba and the like, I suppose you could classify them under sentient creatures, as defined in plato.stanford.edu/entries/consciousness. Oct 1, 2015 at 17:10
  • I'm not sure what to do with that definition of "sentient". It admits transistors!. And unless you want to write a decision function that gives you a clear answer for any organism, no, I don't agree that delineation is almost impossible. There are abundant cases which are quite clear, with plants and bacteria and such very clearly in the "not conscious" camp, and humans and great apes clearly in the "conscious", and a lot of mammals and birds in "very likely conscious". This is true even if you don't know exactly what "conscious" means except it's like what we experience.
    – Rex Kerr
    Oct 1, 2015 at 17:30
  • But how can you ever know that an organism's consciousness is 'like what we experience'? The scope of consciousness is pretty broad, you know. Oct 4, 2015 at 10:46
  • @SamparkSharma - You start by explaining what it is that we experience.
    – Rex Kerr
    Oct 5, 2015 at 18:13

Your question is, in my opinion, a concise version of the most fundamental questions facing philosophy today. To view "consciousness" as a quantifiable construct of "complexity" is to apply to the mind itself what we take to originate from the mind: the methods of reduction, relational reasoning, and mathematization.

It is to pursue a "naturalized epistemology" as recommended by Quine and others. The implication is that, whatever it means to "explain" or "know" something, the other paths open to philosophy's original injunction "know thyself," have proven sterile.

The opposite approach is that of phenomenology, existentialism, hermeneutics, and advanced theology. All the "subject" can know is "itself" through processes of reflection. As Hegel correctly noted "consciousness" is always "self-consciousness" and can be known only through recursive "self" interpretation.

Historically, the basic split in these two approaches to "self-knowledge" arrives with Frege versus Husserl, though versions date back to William of Occam versus Meister Eckhart. In the tradition of Hegel and Marx this problem of self-knowledge pops up again and again as "identity of subject and object." In the analytical tradition it takes the form of the paradoxes of self-reference.

To "know" something is to see it from all side and hence to stand "outside" it. How can consciousness "know itself"? For many philosophers (Church, Metzinger, Dennett) the antiquated term "consciousness" merely obscures the process. It may be that this ancient question will take the form of a collective Turing Test. Hobbes argued that to "know" or "explain" something is simply to be able to reproduce it. The definition of consciousness as "complexity" invites its mathematization, which invites its reproduction in AI.

After all, if we can "know" that the amoeba is mechanically "self-conscious" in the same way we are, we seem to be carrying out this process of "knowing" using the very methods you appear to to deplore. The methods of reductive mathematization are indeed nibbling away at the difference between "consciousness" in the amoeba and ourselves, and the language of "complexity" may soon place them in a theoretical continuum.

  • Could you please explain what you mean by "advanced theology". - If Hegel equates consciousness with self-consciousness I cannot follow him. In general, consciousness is directed onto an object, but directedness must not be reflexive. - Why do think that an amoeba has consciousness, are there any mental processes?
    – Jo Wehler
    Sep 28, 2015 at 10:00
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    By "advanced theology" I mean loosely a theology of logic, such as Thomists or religious Hegelians, not pure revelation. These are traditional sources of an anti-materialist-reductivist stance on "consciousness." I believe Hegel is right that consciousness is reflective and entails a "self," or that which can say "I am.....X" or "I am... NOT X." This is the endless paradox of self-reference and incompleteness that, for many, distinguishes "consciousness" from neural action and reaction. The question is whether one can reduce to the other and the stubborn obstacle of "self" be mathematized. Sep 28, 2015 at 13:52
  • Would I be right in saying that what your answer eventually boils down to is the perplexity over where to place the observer? And you're also saying that there's been much debate over whether we can 'put (as in apply) to the mind something that comes from the mind'. That's the gist of what you are saying, right? Sep 28, 2015 at 16:06
  • @JoWehler Why is it that we look at an amoeba's consciousness in context to ourselves? Even if it isn't aware of itself as a being or an entity, we cannot say that a lack of 'mental processes' (as we know humans to have) automatically disqualifies it from having consciousness. With that said, just like you, I can't quite get what Hegel means by his statement. Sep 28, 2015 at 16:14
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    Hegel's inclusion of a reflective "self" and "self-reference" in the definition of "consciousness" seems very intuitively viable. After all, we do not think of ourselves as fully "conscious" the minute we are born, even though the neural substrate is already hard at work. As we develop and become "conscious of" this or that, we undergo a kind of fissure into "other and "self" and struggle to "see ourselves" as others see us, as if in a complex mirror. In a similar way, Descartes finds that this "I am" is what he cannot subtract from consciousness, if not in that language. Sep 28, 2015 at 17:14

The exact wording is most likely important here (emphasis mine):

but we must assume also that it is only when the organism has reached a certain complexity of nervous structure that the complex of psychic facts reaches the degree of complication that we call consciousness.

The phrasing "we call" invokes linguistic concepts akin to the work of Tarski. "'P' is true if and only if P is true" is the phrasing of his famous definition of Tarskian Truth, and the single quotes call attention to the idea that, while P may be a real thing, 'P' is a linguistic phrasing or concept.

The argument here may be that there is a deep thing that is not quantitative, which is related to the thing we call "consciousness," but that "consciousness" is just a word, to which we can attempt to apply a definition.

It is entirely possible that the thing we call consciousness is something which necessarily entails a particular level of nervous complexity. However, it is also possible that there is something deeper than that which is not intimately entwined with neurophysiology. If that something was given a name, it might be remarkably hard to distinguish from "consciousness," and thus there would be little value in trying to give it any name besides "consciousness."

If one does make the argument that what we call consciousness necessitates some neural arrangement, this may lead us to distinguish between the neural arrangements and that something deeper that was previously hard to see. Linguistically, one of two results can easily happen:

  • This neural arrangement concept is given a new name (perhaps "neural-consciousness"), and the meaning of "consciousness" is adjusted to exclude it, including only the less tangible part.
  • We find the existing definition of "consciousness" actually fits the neural arrangement better, and invent a new word to describe the deeper concept.

Personally, I have great trouble with claiming there is a complexity line-in-the-sand for consciousness too, by the definitions I prefer to use. However, when discussing what "we" as a populace call "consciousness," it does seem reasonable that there is a line that can describe that, for much of what the populace calls "consciousness" permits lines to be drawn.

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