From Towards a Science of Consciousness 3         Section 1: The Expalanatory Gap       CogNet Proceedings

"Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe?"
-Stephen Hawking, A Brief History of Time

I         Introduction

In its original context Hawking was writing about the significance of physics for questions about God's existence and responsibility for creation. I am co-opting the sentiment for another purpose, though. As stated Hawking could equally be directing the question at concerns about the seemingly abstract information physics conveys about the world, and the full body of facts contained in the substance of the world. Would even a complete and adequate physics tell us all the general facts about the stuff the world is made of? In this chapter I am going to argue that the answer is "no." I am also going to argue that the missing facts are like the kinds of facts we can use to cross the explanatory gap. I am going to argue, in short, that we have reasons to re-enchant matter that are independent of the mind-body problem. In a recent anthology on consciousness (1997) Güven Güzeldere has wrote,

a principle reason underlying the confusion and seeming mystery surrounding the concept and phenomenon of consciousness lies in the presence of two influential, equally attractive, pretheoretic characterizations. . . . They can be summarized in the following mottos: "Consciousness is as consciousness does" and "Consciousness is as consciousness seems."

Güzeldere calls these the "two faces" of consciousness. Face one of consciousness concerns the causal role that being conscious enables a cognitive element to play in our mental economy. Face two of consciousness concerns the way conscious elements feel or appear to the experiencer. These two faces correspond to the functional and experiential aspects of the problem, respectively.

By using this distinction we can produce a useful and quick diagnosis of why the explanatory gap exists. Science describes the way the external world seems to us largely by explaining why things do what they do. At intermediate levels we involve structural descriptions in the project, but these are typically only important because of their role in helping us to fulfill the primary goal of understanding the behavior of things. Most centrally, at the bottom level the basic physical things have one "face": when one explains what things at this level do, one has explained all the facts about how they seem. The "one face" of physical things concerns how they behave with respect to other physical things.

The gap arises because the experiential face of consciousness involves facts that seem to go beyond just facts about what it does. In Güzeldere's phrase, unlike physical things, consciousness has "two faces." Facts about the phenomenal qualities, and the experiencing of these qualities, exist as further targets of explanation. So even after our physical theories explain what consciousness does, there are further questions about its nature that we need to ask and answer. These are the "hard problem" questions about its other "face."

II         The Landscape of Responses

Even though some flatly deny the existence of the explanatory gap, its existence is widely perceived and acknowledged by members of the consciousness studies community. Three strategies to address it have been well-explored without yielding a stable consensus. The first strategy involves trying to produce arguments that, despite first appearances, no gap exists. The troublesome experiential face is more or less an illusion, and no facts other than facts about what consciousness does (Dennett 1988, Wilkes 1988, Rey 1995) exist. The second strategy is to argue that, even though there is an explanatory gap, that does not mean we need to draw any conclusions about our theories leaving out any facts (Levine 1993). The gap is merely one of explanation, and so it only draws our attention to a peculiarity in our situation with respect to the facts. Nothing else important follows from it. A closely related third strategy is to argue that a gap merely seems to exist because of some cognitive limitation on our part (McGinn 1989)-we are too stupid (or have the wrong type of intelligence) to appreciate the explanatory connection. A proper understanding of the physical and phenomenal facts would, in reality, show us that one explains the other.

I do not believe any of these three strategies are acceptable. The first simply flatly conflicts with the evidence. Its proponents need to produce much stronger arguments than they have produced to make it a serious contender, and I am pessimistic that such arguments exist. Each of the other two strategies suffers from another serious fault: they are exercises in excuse making. The explanatory gap is an instance of explanatory failure. When confronted with explanatory failure, standard practice in science is to re-evaluate the theory for inaccuracy or incompleteness. These moves attempt to blame the psychology or perspective of the theory makers rather than the ontology of the theory, and are completely anomalous. They stand in the way of the real possibility that we can find a better theory.

In this chapter I will pursue a fourth strategy by tackling the problem more directly. I will show fault in the theories, rather than the theory-makers. My methodology, then, is more traditional than the methodology of the other strategies. The conclusion I reach, however, may seem more radical. I am going to argue that physical things are "two faced" also. More facts than just the facts about what they do are true of them, and these further facts may fill the gap. If this conclusion is correct then the form of the theories traditionally employed in the sciences needs to be supplemented before we can cross the explanatory gap.

Someone pursuing this strategy needs to meet three challenges, which I will try to do. The first challenge is to avoid being ad hoc. To make the strategy work, the motivation for introducing these extra facts should be independent of the mind-body problem. Otherwise the theory is likely to seem-and probably be-indulgent, and will compete poorly in the marketplace of ideas.

The second challenge is to avoid the dualist dilemma. Whatever facts one introduces must be tied to the physical facts in a way that does not make them causally irrelevent, or spookily interactive.

The third challenge is to be relevant to the explanatory gap. The theory must give reasons why these further facts about the physical, whose existence one has independent reason to believe in, may fill the explanatory gap between the physical and phenomenal facts.

III         The Physics of Life

In pursuit of this strategy, I am now going to examine the character of the physical facts. By "the physical facts" I mean, stipulatively, the facts as they are conveyed by physics (or an ideal science relevantly like physics, in a sense of "relevantly" that will become clear). This stipulation immediately produces an expository problem for me, because real physics is complicated and still evolving. Also, people tend to bring distracting suppositions to discussions of it. To get around these problems I am going to work in a simplified context-a simplified physics-that still raises the crucial issues in a clear and direct way. After discussing the issues in this simplified context, I will bring the discussion back to real physics and, ultimately, to the problem of experience.

The toy physics that I am going to consider describes the class of cellular automata called Life worlds. A Life world consists of a two dimensional grid of cells that we visualize as squares with eight neighbors: one neighbor touching each side, and one neighbor touching each corner. Figure 4.1 shows a cell and its neighbors. At any given time, each cell may have exactly one of two properties: the "on" property or the "off" property. For the sake of argument, I am going to stipulate that a cell's being "off" consists in its having some positive property rather than merely the absence of the "on" property. Life's physics consists of three simple rules:

1) If a cell has exactly two "on" neighbors it maintains its property, "on" or "off," in the next time step.
2) If a cell has exactly three on neighbors it will be "on" in the next time step.
3) Otherwise the cell will be "off" in the next time step.

[Figure 4.1 here; Figures not yet available]

This very simple physics can produce very complex phenomena. The automaton gets the name "Life" from the fact that it can produce patterns of "on" and "off" properties that are nontrivial self-replicators in the same mathematical sense that DNA are. One can also build a Universal Turing machine inside a Life world. Let us assume, for the sake of argument, that we have a dimensional viewer that gives us access to another reality, one that is a Life world with a Life world's physics. Since a Life world can support the existence of complexly functioning objects let us also assume that this world supports the existence of objects that function analogously to cognitive systems in our world. That is, their behavior is complex and purposeful seeming, and it is driven by what seems to be an information processing cognitive engine responding to perceptions of its environment. These objects consist of patterns evolving atop the grid, subsisting in huge arrays of cells blinking on and off through time.

Would such Life objects be phenomenally conscious? Most people agree that an explanatory gap seems to exist here also, as a skeptic would have a consistent position (the gap is argued for in Rosenberg 1997). If consciousness were to exist in such a world, its existence would seem like a brute fact relative to the specification of its physics, and relative to the existence of the kinds of properties its physics can transparently support. The presence of consciousness would seem to us like the result of some kind of law of nature, or a "metaphysical" law, or a "metaphysical" identity of some kind. This is just like the situation with respect to the explanatory gap in our world.

Why does the gap exist in the Life world? One very deep reason for the existence of the gap here is that we presume that Life's physics completely characterizes the basic properties in a pure Life. That means these basic properties are completely characterized by:

1) A bare difference of type between them;
2) The roles they occupy in the physical laws.

Focusing on the first condition, what is a bare difference? The phrase is meant to express an intuitive point that can be loosely stated this way. Life's physics leaves us in the dark about what the "on" and "off" differences are themselves. We just know the facts that they are different and enter into certain dynamic relations. Moreover, if we are viewing a pure Life. world then we can assume that there just are no other facts about those properties. The difference is "bare" because it does not rest on any further facts about the properties.

This distinguishes the Life world's bare difference from other cases of difference. In other cases of difference, the facts about difference are implied by other facts. One naturally says that these differences rest on, or arise from, these further facts. For instance, benzene molecules and sodium chloride molecules are different molecules, but all their differences are implied by further, more fundamental facts about their structure and content. As another example, the fact that red and green are different colors seems to rest on further facts about their hues, intrinsic and observable facts about the appearances of those hues.

In more philosophically technical terms, a "bare" difference is a difference relation that is ontologically primary instead of being implied by other facts. When a "bare" difference obtains, the natures of the relata are constituted by their participation in the relation but not vice versa. In this way the relation of difference is the ontological ground, and the existence of the things related is derivative on it. This is in contrast to the usual kind of difference relation in which the relata are the ontological ground, and the relation is derivative on intrinsic facts about them.

The skeptic about the existence of consciousness in a pure Life world doubts that a mosaic of bare difference could support the existence of consciousness. A pure Life world would be constituted by a mosaic of bare difference, and the absence of consciousness seems consistent with the presence of any mosaic of bare difference. Consciousness, the skeptic claims, is not pure pattern. The skeptic even has an argument for this position:

1) Difference relations between phenomenal qualities are observable.

2) These difference relations are observably contentful relations: it is not a formal relation of bare difference. For example the difference between red and green holds because of facts intrinsic to redness and greenness.

3) These phenomenal contents themselves are observably not structures of bare differences.

For the skeptic these are not just "intuitions." They are observable facts about a class of everyday phenomena. As observations go, they can in principle be overturned, but that will take an extremely strong argument. At this point, how will the argument with the skeptic go? I can report from experience that there will be stubbornness and fist pounding on both sides. The skeptic's opponents will make appeals to something called metaphysical necessity that neither of them really understands, or to a fact of primitive identity that is unlike any identity discovered elsewhere. Someone will make an appeal to the skeptic's epistemic frailty, charging that the skeptic cannot reliably make the consistency judgments needed.

Among all this sound and fury something is being overlooked. The debate with the skeptic suggests a question. Could there be a pure Life world? That is, could a world exist in which no fundamental facts were true except those completely characterized by the Life physics? If not, then even a completely adequate physics for a Life world would fail to deliver all the facts about that world. Some further facts would need to be present to complement the physics and complete the world.

I think several reasons exist for believing that a pure Life world could not exist. First, the basic "on" and "off" properties of Life are characterized by their dispositional relations to one another, and the dispositional network is circular. The kind of circularity present is a special kind of logical regress. If one wishes to know what the "on" property is, one is told that it is the property that is not the "off" property, but is dispositionally related to it in a special way. That is acceptable as long as we know what the "off" property is. What is it? According to the physics, it is the property that is not the "on" property, but is dispositionally related to it in a certain way. This would be adequate if we knew what the "on" property is, but that is where we started.

The description is completed by positing that the relation of difference is one of bare difference, an ontological ground that constitutes the properties. This is difficult, though, because a difference relation between properties is-in all other instances-grounded in further facts. We have no precedent for understanding what a bare difference between properties is. The precedents we do have tell us that properties characterized by circularly defined categories and higher-order relations belong to abstract schemas. That raises the question of how nature instantiates these schemas, and the properties internal to them. Are they self-sufficient?

In all other instances, the elements of a schema require carriers. What is a carrier? A carrier is something that exists within an instance of a schema even though it has a nature outrunning the categories of that schema. To be a carrier this nature must be capable, in the proper context, of playing the part of a schema element by helping to instantiate the structure of relations required by the schema. When this happens we often say that the carrier is implementing some element of the scheme.

To qualify as carriers items must have intrinsic relations to other carriers-relations of difference or dynamics-that mirror the stipulated relations in the schema. These "intrinsic" relations are just relations that hold between their schema independent natures. For instance, we can implement a game of Life on a checkerboard by using red and black checkers; or in a computer using voltages. The red and black checkers can be carriers because of a prior relation of difference between their hues. This prior relation of difference can stand in for the stipulated relation of difference between the "on" and the "off" properties. Finally, by affecting the humans in their surroundings in ways that cause them to manipulate the board in accord with the physics, the checkers acquire the dispositional properties needed, albeit in a roundabout way. Similarly, the voltages in a computer have natures outrunning the categories of Life, but which, in the proper context, exhibit relations to one another that mirror the stipulated relations of the schema.

A carrier that has a nature outrunning one schema-a nature external to that schema-may still be internal to another schema. The relationship between molecules and genes follows this pattern. In describing genes, genetics describes a schema for transmitting information. Its elements are carried by organic molecules like DNA. But molecules themselves belong to another schema, that of molecular chemistry, which is described by the rules of the periodic table. The schema of the periodic table is itself carried by the schema of atomic chemistry, and, ultimately, quantum physics.

Nested layers of pattern and being could also exist in the Life world, creating a similar ladder of embedded schema within schema. What happens when we get to the bottom (i.e., Life physics?) We do not want to regress indefinitely, but we still have a schema. We still need carriers for the basic properties. To avoid a regress these carriers will have natures that are partially external to the fundamental system of categories in the fundamental schema, while not being internal to any other schema. To meet these conditions these fundamental carriers will need to be intrinsic properties, understood as properties that cannot be fully characterized through the relations they enter into with other properties. For any physical story about them-stories about the difference structures they instantiate and the lawful relations they enter into-there will be further facts to know. These further facts will be intrinsic facts that carry the fundamental nomic dispositions, and that carry the fundamental facts of difference in type and quantity.

If this view is right, there could not be a "pure" Life world. The notion of a "bare" difference, in the end, does not make sense. Any Life world would at least have to contain further facts about the intrinsic natures of the carriers. These facts would not be reducible to the facts about the relations specified in its physics. These points raise the question, "Is our physics in any better shape than Life's physics?"

An examination of our physics does not yield reasons to believe that it is. We have fundamental properties like "mass," "spin," and "charge." We characterize these almost exactly like we characterize the "on" and "off" properties. There is one difference in that our physics contains added indexical facts. These facts allow us to pick out the various roles by using our community as a kind of central pivot point from which we can begin plotting the system of relations. Such indexical facts anchor how the schema should be mapped onto the elements of our world, but they do not touch the fundamental problem. That problem concerns the natures of the things that we are mapping to.

From these points it seems to follow that there is at least one category of fact left out by our physical explanations: facts about the carriers. Furthermore, these facts will be facts about intrinsic natures that have internal relations of difference, scalar variation along selected dimensions, and that carry lawful dispositions with respect to one another. The main point of this chapter should now be apparent: this description fits the phenomenal qualities perfectly. The two "problems," that of finding a place for the phenomenal qualities and conceiving of what the carriers must be like, fit together like lock and key.

The view also meets the three challenges laid out at the beginning of the investigation. First, it is not ad hoc. Both the carrier problem and the hypothesis about their natures were introduced independently of the mind-body problem, and of any strong theoretical suppositions about the nature of the phenomenal properties. Second, it avoids both epiphenomenalism and interactionism. In a sense, the phenomenal properties show up as the deep nature of the physical. They are the stuff that is doing the work. Physics is only a partial description of the work that is getting done. Finally, making the supposition that phenomenal properties are the carriers in this world holds promise as a way of crossing the explanatory gap. For we would no longer be trying to derive the existence of the contentful character of experience from an abstract description. Instead we would be trying to understand how such an abstract description, a description of structural and quantitative variation, and of nomic compatibility, could derive from a contentful base. This seems like an easier task, especially since we already know that phenomenal contents do have internal difference relations, scalar variations within families of qualities, and intrinsic compatibility and incompatibility relations. Points like this have been made several times before (e.g., Whitehead 1929, Russell 1927, Maxwell 1978, and Lockwood 1989) but the idea's potential seems to have been lost in all the commotion about zombies, "metaphysical" necessity, epistemic limitations, and the like.

IV         The Two Faces of Causation

As intriguing as the argument for the two faces of the physical is, the problem of crossing the explanatory gap lies deeper still. The argument so far only provides a reason for believing in some intrinsic facts about the physical that are not characterized by physical science. To successfully cross the explanatory gap we need to answer at least two further questions. The first question concerns why these intrinsic properties should be experiential in character. A gap seems to exist between mere intrinsicness and experiential intrinsicness, as the experiential character seems to be an added aspect. A skeptic might ask, "Couldn't there be intrinsic properties that are not experiential?" This gap may not seem as large as the physical/phenomenal gap, but it is real. The second question concerns how one climbs the ladder of nature to account for animal consciousness. While the arguments for the second face of the physical provide reasons for postulating an intrinsic aspect to the elements of the fundamental schema, these elements are just the basic quarks or strings that might lie at the base of physics. There is still a huge gap between that level, and the level where we need an explanation of the intrinsic content that one would identify with animal consciousness.

In this section I am going to gesture toward a place in theory space where we can address these further questions, and I am going to do this by outlining a proposal that I develop in detail in Rosenberg (1997). The key proposal begins with two points. First, the fundamental schema will be the schema that describes the world's causal structure. Second, the schema of physics describes only an aspect of this more fundamental schema. Fundamental physics describes the regularities in the ways that the basic effective properties instantiate, but there is more to causation than this. The schema of the world's causal structure has two faces itself, and these faces correspond to the effective and receptive aspects of causation. In general, physics does not contain a theory about the nature of the causal connection, nor of the structure of the causal nexus once such natures are included. Huw Price (1997) argues for the this conclusion about physics, and then draws an irrealist conclusion about the existence of causal connections. Rosenberg (1997) argues for the conclusion about physics also, but then motivates and develops a realist theory of causal connection. If this latter reaction is correct, then even a completed physics would be an incomplete description of the world's fundamental facts.

Under the realist alternative the causal nexus has two aspects, its effective and its receptive faces. These two faces are logically inseparable, as one cannot have receptiveness without effectiveness, and vice versa. The natural relation between these two faces will constitute a causal nexus. Since a realist wishes to find a theory of this nexus, a theory of the causal nexus must be a theory of the detailed relation between these two faces.

First, finding the most general theory of the causal nexus requires overcoming one tempting view. This is the view that conceives of the receptive and the effective properties of individuals as each being monadic properties of those individuals. In place of this common sense picture, one must substitute a picture of receptivity as a connection between the effective sides of distinct individuals. Figure 4.2 illustrates these two alternatives. When one models receptivity as a connection, the receptive connection does the work of the causal connection, and causation emerges by detailing the conditions under which this connection might bind two or more effective states.

[Figure 4.2 here; Figures not yet available]

Modeling receptivity in the way described above yields several important explanatory benefits. Among these are,

1) It enables the theory to sidestep questions about adding further conditions for deciding when an individual is receptive to another individual (e.g., spatiotemporal contiguity) over and above sharing a receptive connection. This allows it to take a simpler form by making fewer assumptions at the outset, and ultimately makes it more compatible with modern physics.

2) It yields a simple inductive definition of natural individuation that enables the theory to elegantly model levels of nature, where those levels each contain irreducible individuals with irreducible aspects. The definition is as follows: an individual is a natural individual IFF

Base case:

Inductive case:

3) It yields a topology to the causal mesh that increases the explanatory power of the theory by allowing for a reduction of the facts about spacetime to facts about causal connection and causal significance.

4) It yields a structure for the causal nexus that ties into the hypothesis that consciousness is a carrier for causal content, and does so at a deep and detailed level.

When developed the theory yields an intriguing way to view the world, one that endows it with an intricate vertical structure that is more than merely pattern atop pattern. This way of viewing the world is depicted in figure 4.3.

[Figure 4.3 here; Figures not yet available]

To understand what this view involves one must fully appreciate the role of receptivity in the creation of natural individuals at different levels. A natural individual's receptivity is an element of its being that binds lower-level individuals within it, making those individuals effective states relevant to one another in a direct way. As such, receptivity is an irreducible global property of a natural individual. The term irreducible here is being used in its strongest sense: a higher-level individual's receptivity is not the sum, either linearly or nonlinearly, of the receptiveness of its lower-level constituents. It is a novel element in the world, unique to the individual that it helps constitute.

The role receptivity plays is that of a possibility filter. By opening a group of individuals to the constraints presented by one another's effective properties, it maps a set of prior possibilities for the joint states of its constituents onto one of that set's proper subsets. That is what allows it to play the role of a causal connection, as its presence imposes a condition on the joint instantiation of states that sunders their independence from one another. The theory, then, is highly nontrivial. The addition of receptivity to a model of the causal nexus not only represents a substantial metaphysical hypothesis, but, in principle, one should be able to draw substantial empirical hypotheses from it also. As an irreducible global property it echoes of the sort of thing that draws people to quantum mechanical theories involving global coherence; as a possibility filter it echoes the sort of thing that attracts people to theories of quantum decoherence. In the end it is a sort of hybrid notion whose full implications need to be explored.

Because of the irreducible nature of each receptivity, the theory needs something to carry each instance of it, and also the effective constraints active within that individual. Here we see a duality to causation: it divides into the existence of effective constraints, and the binding of those constraints within a shared receptivity. Furthermore, these two aspects are logically connected to one another in a kind of compositional circularity. For an instance of receptivity to exist, it must bind effective constraints; and for the effective constraints to exist, they must be bound within an instance of receptivity. Although they are distinct kinds, they are logically inter-dependent.

Consciousness, we have already noted, also divides into a kind of duality. At the beginning of this section, I noted the intrinsic properties that are its contents, and the experiencing of those properties. This division in consciousness seems conditioned by a mutual dependence similar to the mutual dependence of the effective and receptive aspects of the causal nexus. The qualities of experience must be bound within an experiencing subject (for them, to be is to be experienced); and for a subject of experience to exist, it must experience phenomenal qualities. Perhaps this is an instance of a kind of de re logical relationship between distinct essences, as their independence is (arguably) inconceivable. This point holds promise in solving one of the problems the carrier view is confronted with. Namely, it may help us to understand why the intrinsic properties of the world are experiential properties. The answer may be that the intrinsic content is carrying effective constraints, and the experiencing of that content is the result of a shared receptivity.

Further, we have a natural ladder of nature in our picture already, and climbing it does not require combining qualities from lower levels into a mix that somehow yields the qualities at the higher levels. It merely requires mapping each lower-level effective property appropriately to an irreducible carrier at the next level. What qualifies a carrier in a particular instance is an appropriate match with the constraint it must carry from the lower-level individuals. This constraint should be mathematically describable using a set number of degrees of freedom along which the constraint may vary, and laws describing the ways that other states are effected by its variance. To carry it, the phenomenal quality would need to instantiate the dimensional structure of this characterization, and belong to a family of qualities whose internal compatibility and incompatibility relations mirror the laws.

To understand how the ascent is achieved, one can use an analogy to vector addition. Such addition directs you to a new vector in the space in a rulelike way, but it does not mix the old vectors as if they were building blocks of the new. To understand how to get from level to level in the view I have proposed, imagine a vast quality space that partitions into families. These qualities are potential carriers for effective constraints. The effective states of lower-level individuals present these effective constraints to other individuals when they become bound within a common receptivity. This constraint may have degrees of freedom corresponding to the structure of the individual that presents it. Think of the lower-level individual as being constitued by a set of vectors, and the constraint it presents is like doing a sum over those vectors. It yields a new vector that takes us to a new place in quality space. Thus what we are searching for are projection operators that jump us through quality space, moving us from one family of qualities to another. We are not faced with the problem of finding combinatorial operators that create new qualities from alien ones. In short, the intrinsic qualities at lower levels are stepping stones to the qualities at the higher-levels, not constituents of those qualities. If this is correct, we can solve both of the original problems this section started with. The instrinsic nature of the world is experiential because experience is needed to carry the receptivity of the causal nexus. Nature does not create the qualities of animal consciousness by throwing together alien qualities at lower levels. They are reached by taking an orderly walk through quality space as nature drafts different carriers into duty in service of individuals at different levels.

These suggestions are intriguing enough to make one wonder if consciousness can map to the carrier role. Table 4.1 lists a partial answer to this question (in fact, the mapping can get much more detailed).

Table 4

In conclusion, this view of the two faces of causation yields two fundamental hypotheses that hold promise that we may yet bridge the explanatory gap. These hypotheses are:

The Carrier Hypotheses Phenomenal qualities carry the effective constraints in the world; the experiencing of those qualities by a subject carries the receptivity of an individual to those constraints.

The Consciousness Hypotheses Human consciousness is carrying the causal content of a high-level, cognitively structured, natural individual. Human awareness is experiential acquaintance with the intrinsic content that carries nature's effective side.

References

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