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Trying to define conscious experience in terms of more primitive notions is fruitless. One might as well try to define matter or space in terms of something more fundamental.
When someone strikes middle C on the piano, a complex chain of events is set into place. Sound vibrates in the air and a wave travels to my ear. The wave is processed and analyzed into frequencies inside the ear, and a signal is sent to the auditory cortex. Further processing takes place here: isolation of certain aspects of the signal, categorization, and ultimately reaction. All this is not so hard to understand in principle. But why should this be accompanied by an experience? And why, in particular, should it be accompanied by that experience, with its characteristic rich tone and timbre?
Among the many varieties of visual experience, color sensations stand out as the paradigm examples of conscious experience, due to their pure, seemingly ineffable qualitative nature.
The sense of self. One sometimes feels that there is something to conscious experience that transcends all these specific elements: a kind of background hum, for instance, that is somehow fundamental to consciousness and that is there even when the other components are not. This phenomenology of self is so deep and intangible that it sometimes seems illusory, consisting in nothing over and above specific elements such as those listed above.
At the root of all this lie two quite distinct concepts of mind. The first is the phenomenal concept of mind. This is the concept of mind as conscious experience, and of a mental state as a consciously experienced mental state. This is the most perplexing aspect of mind and the aspect on which I will concentrate, but it does not exhaust the mental. The second is the psychological concept of mind. This is the concept of mind as the causal or explanatory basis for behavior.
On the phenomenal concept, mind is characterized by the way it feels; on the psychological concept, mind is characterized by what it does.
In philosophy, the shift in emphasis from the phenomenal to the psychological was codified by Gilbert Ryle (1949), who argued that all our mental concepts can be analyzed in terms of certain kinds of associated behavior, or in terms of dispositions to behave in certain ways.
These problems were finessed by what has become known as functionalism, which was developed by David Lewis (1966) and most thoroughly by David Armstrong (1968).8 On this view, a mental state is defined wholly by its causal role: that is, in terms of the kinds of stimulation that tend to produce it, the kind of behavior it tends to produce, and the way it interacts with other mental states.
It is related to the idea that belief is something of an explanatory construct: we attribute beliefs to others largely in order to explain their behavior.
There is no vast metaphysical problem in the idea that a physical system should be able to introspect its internal states, or that it should be able to deal rationally with information from its environment, or that it should be able to focus its attention first in one place and then in the next. It is clear enough that an appropriate functional account should be able to explain these abilities, even if discovering the correct account takes decades or centuries. But the really difficult problem is that of phenomenal consciousness, and this is left untouched by the explanations of psychological
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They may be different facts (a fact about elephants is not a microphysical fact), but they are not further facts.
A reductive explanation of a phenomenon need not require a reduction of that phenomenon, at least in some senses of that ambiguous term. In a certain sense, phenomena that can be realized in many different physical substrates—learning, for example—might not be reducible in that we cannot identify learning with any specific lower-level phenomenon. But this multiple realizability does not stand in the way of reductively explaining any instance of learning in terms of lower-level phenomena.20 Reductive explanation of a phenomenon should also not be confused with a reduction of a high-level
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The paradigm of reductive explanation via functional analysis works beautifully in most areas of cognitive science, at least in principle. As we saw in the previous chapter, most nonphenomenal mental concepts can be analyzed functionally.
Unfortunately, the kind of functional explanation that works so well for psychological states does not seem to work in explaining phenomenal states. The reason for this is straightforward. Whatever functional account of human cognition we give, there is a further question: Why is this kind of functioning accompanied by consciousness?
reductive explanation is not the be-all and end-all of explanation. Its chief role is to remove any deep sense of mystery surrounding a high-level phenomenon. It does this by reducing the bruteness and arbitrariness of the phenomenon in question to the bruteness and arbitrariness of lower-level processes. Insofar as the low-level processes may themselves be quite brute and arbitrary, a reductive explanation may not give us a deep understanding of a phenomenon, but it at least eliminates any sense that there is something “extra” going on.
Given an instance of high-level causation, such as a released trigger causing a gun to fire, we can not only isolate a bundle of lower-level facts that fix this causation; we can also tell a fairly simple story about how the causation is enabled, by encapsulating those facts under certain simple principles.
If all goes well, biological phenomena may be explainable in terms of cellular phenomena, which are explainable in terms of biochemical phenomena, which are explainable in terms of chemical phenomena, which are explainable in terms of physical phenomena. As for the physical phenomena, one tries to unify these as far as possible, but at some level physics has to be taken as brute: there may be no explanation of why the fundamental laws or boundary conditions are the way they are.
On a careful analysis, I think that it is not hard to see that this is wrong, and that the high-level facts in question are (globally) logically supervenient on the physical insofar as they are facts at all.35 Conscious experience is almost unique in its failure to supervene logically. The relationship between consciousness and the physical facts is different in kind from the standard relationship between high-level and low-level facts.
I am making the much weaker claim that high-level facts are entailed by all the microphysical facts (perhaps along with microphysical laws). This enormously comprehensive set includes the facts about the distribution of every last particle and field in every last corner of space-time: from the atoms in Napoleon’s hat to the electromagnetic fields in the outer ring of Saturn.
All our sources of external evidence supervene logically on the microphysical facts, so that insofar as some phenomenon does not supervene on those facts, external evidence can give us no reason to believe in it.
Somebody might conceivably hold that inverted spectra but not zombies are logically possible. If this were the case, then the existence of consciousness could be reductively explained, but the specific character of particular conscious experiences could not be.
Even if we knew every last detail about the physics of the universe—the configuration, causation, and evolution among all the fields and particles in the spatiotemporal manifold—that information would not lead us to postulate the existence of conscious experience. My knowledge of consciousness, in the first instance, comes from my own case, not from any external observation. It is my first-person experience of consciousness that forces the problem on me.
For example, from these facts one could ascertain that there were a lot of organisms that claimed to be conscious, and said they had mysterious subjective experiences. Still, this evidence would be quite inconclusive, and it might be most natural to draw an eliminativist conclusion—that there was in fact no experience present in these creatures, just a lot of talk. Eliminativism about conscious experience is an unreasonable position only because of our own acquaintance with it.
Although conscious states may play various causal roles, they are not defined by their causal roles. Rather, what makes them conscious is that they have a certain phenomenal feel, and this feel is not something that can be functionally defined away.
Given any account of the physical processes purported to underlie consciousness, there will always be a further question: Why are these processes accompanied by conscious experience? For most other phenomena, such a question is easily answered: the physical facts about those processes entail the existence of the phenomena. For a phenomenon such as life, for example, the physical facts imply that certain functions will be performed, and the performance of those functions is all we need to explain in order to explain life. But no such answer will suffice for consciousness.
From a methodological standpoint, it is not obvious how one can begin to develop a neuroscientific theory. How does one perform the experiments that detect a correlation between some neural process and consciousness? What usually happens is that theorists implicitly rely on some psychological criterion for consciousness, such as the focus of attention, the control of behavior, and most frequently the ability to make verbal reports about an internal state. One then notes that some neurophysiological property is instantiated when these criteria are present, and one’s theory of consciousness is
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It might be supposed that there could eventually be a reductive explanatory technique that explained something other than structure and function, but it is very hard to see how this could be possible, given that the laws of physics are ultimately cast in terms of structure and dynamics. The existence of consciousness will always be a further fact relative to structural and dynamic facts, and so will always be unexplained by a physical account.
