This one was a bit tougher...
Consciousness
As mentioned in the Introduction, Descartes (and Galileo) did something during the scientific revolution in the 17th century that led to our current problem: they invented the concept of 'objective physical reality.' They split the world in two: (1) an external, 'objective' reality that extended throughout space and time and could be observed, measured and described mathematically (e.g., size, shape, motion--'primary qualities'), and (2) an internal, 'subjective' reality of appearances assigned to the mind (color, sound, smell, etc.--'secondary qualities'). Primary qualities were essential to the things in question, while their secondary features were just that: secondary, less essential, more 'subjective.' Because human perception of the world only dealt with such 'secondary' qualities, it was left out of the scientific study of 'objective reality.' So, such pioneers of science used their senses to derive conclusions about reality, but ignored their very ability to take in those sense-data in the first place: consciousness, subjectivity, experience. We're still under the influence of this gross error.
But humans are part of objective reality, as are our perceptions and the central nervous systems that make those perceptions possible. We're composed of the same stuff as the universe. And the very existence of consciousness is a mystery. It seems to imply "that the physical description of the universe, in spite of its richness and explanatory power, is only part of the truth, and that the natural order is far less austere than it would be if physics and chemistry accounted for everything." The thing that scientists ignored (and continue to ignore) actually points to a far more complex universe than simple 'objective reality' suggests.
So how do materialists, who think that "only the physical world is irreducibly real" (i.e., only matter is fundamentally real; everything else can be explained in terms of it and it alone), account for minds? Various theories have come and gone, including various types of behaviorism. Behaviorism took Descartes' error to an extreme, saying that mental experiences were the same thing as the behaviors or actions that accompanied them. So, a smile was the same thing as 'being happy.' In fact, because only what is observable and measurable is real (there's Descartes' error again), 'being happy' was no more than a smile. The really extreme behaviorists would say there is no such thing as being happy, only smiles. Subjective experience is an illusion. Mental states are no more than the facts that outside observers can observe, in order to say that such a state has indeed occurred. (In jargon, it's a 'verificationist' theory, because it needs verifiable data, not subjective experience, which can't be verified by anyone other than the person experience it.) Your happiness is only real because you smiled, or your brain waves showed a certain pattern of activity. That's the extent of its reality.
Next there is "psycho-physical identity theory." According to this theory, brain states are mental states. They are two ways of describing the same thing, the same way that H20 and water are two ways to describe the same thing. So pain is the same as the physical event that occurs in the brain when someone is in pain. But how? It's pretty difficult, because 'pain' and 'pain brain state' don't have the same meanings. Pain is naturally understood as a subjective experience, and a brain state is naturally understood as a pattern of activity in the brain. How can they explain pain as a brain state, without appealing to anything nonphysical? To get around this, they tried to connect all these aspects in a chain of cause and effect: the inner state causes certain behavior, and is caused by certain external stimuli. So, an external stimulus (a pin prick) causes the inner state (pain), which causes a behaviour (facial expression, brain state).
There's a reason it's hard to follow these theories and what they're actually trying to say. That's because they're all trying force a square block through a circular hole. No matter how many ways you try to describe something in terms of something that it's not, it's not going to work. No matter how you try to phrase it, you can't reduce subjective experience. No matter how detailed our explanations can be regarding brain states, there's no possible way such a description can also explain the fact that "I am," and "I experience." There's no other way of describing it except for what it is: direct, subjective experience. It's irreducible. We can describe chemical molecules, but not taste; spectra of light, but not color; neurochemistry, but not emotion. Eyes do not necessarily imply seeing, nerves feeling, ears hearing, etc. All these theories leave out something essential: "the inner mental state itself."
The problem with identity theory is that "H20=water" is sound; it's fully explanatory and it makes sense. Water is nothing but H20, plain and simple. And I can't possibly conceive of a circumstance where H20 does NOT equal water. On the other hand, "It seems conceivable, for any [brain state], that there should be [a brain state] without any experience at all. Experience of taste seems to be something extra, contingently related to the brain state--something produced rather than constituted by the brain itself. So it cannot be identical to the brain state in the way that water is identical to H20." In other words, emotions are more than just brain chemicals; color is more than just light wavelengths, flavor is more than just chemicals, etc. Our subjective experiences may be intimately and strictly tied to what occurs in our brains, but that does NOT mean that brain states are the full explanation.
All this points out just how much difficulty materialists have explaining conscious subjects and their mental lives--"irreducibly subjective centers of consciousness." We'll probably need entirely new concepts to understand the connection between brain and mind, concepts which would would explain what otherwise seems incomprehensible, and this would probably require a revolution on par with relativity. It may not be that subjective experience is something 'produced' by brain states (or 'contingent' on them). That's probably an illusion. It may well be that there is a necessary connection between them. This dual external-physical / internal-mental complexity might pervade the whole world. As Nagel writes, "if psychophysical reductionism is ruled out, this infects our entire naturalistic understanding of the universe."
In this sense, if we're going the 'anti-reductionism' route, it can definitely be seen as a highly "extravagant and costly" position to take. Let's start by looking at what it means for evolution. Even if materialism could give a good account of the origin of life (the first self-reproducing organisms), it would also have to account for the origin of consciousness. And any good theory of consciousness would have to account for the fact that the appearance of consciousness on earth seems closely dependent on the life forms in which it is developed. In other words, a good physical theory has to account for the appearance of the mental aspects in the world. And a good mental theory has to account for why consciousness seems so dependent on physical forms. Either way, evolution is has to be part of the picture, in one form or another.
So what kind of evolutionary explanation, if any, can account for conscious subjects? As pointed out a few paragraphs above, consciousness is "logically distinct" from matter and materialistic wiseacreings: if materialism could account for evolution and the development of nervous systems, it still couldn't account for subjective experience. But there's a fine distinction here. It may also be the case that consciousness needs this complexity in order to appear in the first place, i.e., complexity as a causally necessary and sufficient condition for consciousness. But even this would still require something else in addition to materialism, to account for subjective experience. We need an actual explanation to understand why and how the cause (complexity) produces the effect (consciousness). The two must be explained together. Because materialism can't do this, it can't be the whole truth: "something fundamental must be changed in our conception of the natural order that gave rise to life" if we are to understand why consciousness "was to be expected or how it came about."
Assuming that the universe is fundamentally intelligible, that there is some inherent order to make sense of, we should be able to understand and explain it. But not all things need that 'deep' level of explanation; some things are just coincidence. And just because you know the cause of something, that does not necessarily mean you have fully explained it. For example, take the deaths of four near relatives in a very short time period. Even if I know the direct causes of each of the four deaths, that still doesn't explain the coincidence. There may be something else that explains why it was likely to occur this way, and not another--some relation that makes it intelligible (e.g., a vendetta or genetic disease). As another example, when I type "3+5=" into a calculator, "8" appears. I know the cause (i.e., I pressed the buttons), but there's something else necessary to fully explain it (e.g., the governing algorithm, programmed by its designer).
It's always possible that events like these can be just coincidences. The deaths could just be a freak event, or the calculator may have no real programming, or just be programmed to give "8" as the answer to any buttons I push. "But systematic features of the natural world are not coincidences … Regularities, patterns, and functional organization call out for explanation." If we see such patterns for what they are, but can't explain them, we naturally conclude that our knowledge is lacking in some area; but if we gain that unknown 'something,' it would make everything make sense. The facts would be rendered intelligible.
Similarly, we can see cause and effect in evolution (increasing complexity as a result of natural selection, leading to conscious beings), but we still don't have a full explanation or why it occurred in this way and not another. If we ignore consciousness for the moment, evolutionary theory has to explain why it was likely that accidental mutations led to enough variation to promote evolution; why it was likely that matter evolved into life by chance (i.e., replicating molecules and ribosomes). In other words, it has to explain why it seems so counter-intuitive, so unlikely to have happened the way it actually did. And even if it could (right now it can't), it would still also have to account for consciousness.
If dualism were true, and mind existed as some absolutely separate and distinct 'thing,' evolutionary theory wouldn't have to account for consciousness, but it would still have to account for why evolution produced organisms "capable of being occupied by and interacting with minds." (But, again, this seems rather unlikely--as if matter just so happened to evolve in order to somehow create an adequate body to connect up with mind, and to do so repeatedly and consistently throughout evolutionary history.)
Because of these problems, evolutionary theory must be revised. It can't just state the observable fact that different animals have different consciousnesses, writing off that fact as a "mysterious side effect" of evolution. If the world is intelligible, there's got to be a better answer than that: "a general psychophysical theory of consciousness would have to be woven into the evolutionary story, one which makes intelligible both (1) why specific organisms have the conscious life they have, and (2) why conscious organism arose in the history of life on earth." Again, if evolutionary theory could answer the first question, it still couldn't answer the second. What's needed is what Nagel calls a "conjunctive explanation."
Taking our previous example, tapping "3+5=" (A) explains why "8" appears (B). 'A' explains 'B,' and and 'B' has a consequence (C): the calculator got the right answer. But 'C' doesn't explain WHY the calculator got the right answer. It's just a statement of fact: it got the right answer. A full explanation requires "some further, internal relation between A, B, and C. There must be something about A itself that makes C a likely consequence." In other words, an engineer programmed the calculator with an algorithm, so when I type "3+5=", getting the answer '8' is a likely consequence. Nagel relates this to evolution: "I believe that if A is the evolutionary history, B is the appearance of certain organisms, and C is their consciousness, this means that some kind of psychophysical theory must apply not only non-historically, at the end of the process, but also to the evolutionary process itself."
Let's take this apart. A explains B: evolutionary history explains the appearance of organisms. B has consequence C: the organisms have consciousness. Nagel is saying that there needs to be some kind of internal connection between the historical process (Becoming) and the non-historical aspect (Being). Eight was the right answer because the calculator was programmed to give the right answer; perhaps complex beings are conscious because the universe is 'programmed' to give rise to conscious beings. (Not programmed in the sense of an 'intelligent designer,' but programming somehow woven into the fabric of the universe.) We need to add consciousness to our physical understanding, as playing an active role in the survival of organisms, having hereditary features, and contributing to an individual's 'genetic variation.' But we're still left with the double mystery of Being and Becoming: what is the nature of the relation between the physical and the mental? how do we transform our current physical understanding of evolution to explain how consciousness co-developed with bodies?
As Nagel puts it, a good explanation will have these two elements: "an ahistorical constitutive account [Being] of how certain complex physical systems are also mental, and a historical account of how such systems arose in the universe from its beginnings [Becoming]." Becoming is the outcome of Being, and Becoming has to account for the Being of complex organisms. In other words, something about the structure of the universe leads to the development of conscious beings, and the course of development has to explain how it reached its end results.
There are two possible ways of explaining Being (i.e., the constitutive question). It is either reductive (not to be confused with reductionist) or emergent. Reductive means that everything can be explained by 'reducing' things down to the parts that make them up. So, a reductive explanation of Being will explain consciousness of complex beings "entirely in terms of their elementary constituents." And since the mental cannot be reduced to physical, these constituents will not be merely physical. (And since we're made of the same stuff as the universe, this implies that the stuff of the universe is itself not merely physical!) In other words, everything in the universe can be reduced to one thing: mental/physical 'stuff.'
An emergent account, on the other hand, will explain consciousness as something that 'emerges' only when certain levels of complexity are reached, e.g., central nervous systems. Some principles link mental states and complex physical activity. So, it's different from the reductive account because the connections only apply to complex organisms, not the individual parts that make them up. So If evolution can explain the historical appearance of complex beings on its own, it can be compatible with an emergent approach. But an emergent account needs to systematically explain the connection between mind and complexity, not just observe that they appear together. But this is tricky, because it means that organisms somehow have a mental aspect that ISN'T grounded in the stuff that makes those organisms. As mentioned previously, how likely is it that physical matter, simply by virtue of being combined in certain ways (and by chance, at that!), would reach a state that allows it to connect with 'consciousness.' (And what is the nature of this consciousness? There's Descartes' dualism again.) Seems kind of far-fetched.
It's natural to think that whatever's true of the whole must be true of the parts. Take water. When hydrogen and oxygen combine to make H20, water's liquid quality 'emerges' from this higher level of organization and complexity of its parts. But the features of water are still grounded in, and can be explained in terms of, the elements that make it up. We don't need to add anything 'extra' to our understanding. But consciousness seems to be something completely new. It's hard to grasp how non-conscious parts can somehow combine and suddenly become conscious simply because they combined in some specific way. If the world is indeed intelligible, we'll probably have to give up on the emergent account and look closely at the reductive one. This will be a "general monism" (i.e., a unified base to the universe, one single substance or reality), where "the constituents of the universe have properties that explain not only its physical but its mental character." The mental/physical 'stuff' would evolve to higher levels of complexity--from physics and chemistry to life, and then to conscious beings. Some mental aspect would be present from the very beginning, becoming more complex and more conscious as the universe became more complex.
So, this theory would say that brain states ARE mental states, kind of like identity theory. The difference would be that the physical description is only part of the picture, not the whole shebang. Consciousness isn't a side effect of brain processes (as in an emergent account); brain processes are more than just physical. And since we're taking the reductive route here (universal monism), this goes all the way down to the roots of matter. It doesn't make sense to think of matter as simply 'dead stuff'; rather, "all the elements of the physical world are also mental." In other words, panpsychism. Mind permeates the universe.
Panpsychism may help us to understand how conscious beings can exist in the first place--because mind is part of everything, part of the essential Being of the cosmos--but we're still left with a problem. How can we explain how bits of this 'panpsychic stuff' combine in ways to give rise to the specific types of consciousness we see around us and experience for ourselves? To solve this one, we need to move on to the historical problem: Becoming. Here we have three possibilities: mechanical cause-and-effect (causal), purposeful development (teleological), and divine intervention (intentional).
With cause-and-effect, evolution is understood pretty much as we already understand it: elementary parts of the universe governed by physical laws, bumping into each other until they happen to form RNA/DNA, proteins, etc. Then natural selection takes over and chance survival results better adapted species.
Teleology adds something to those physical laws: "principles of self-organization or of the development of complexity over time that are not explained by those elemental laws." In other words, in addition to chance, there is also some principle in the universe that causes physical laws to be directed in certain ways, for matter to take certain forms and not others. It's not just by chance that life developed; the universe has goals, and matter self-organizes to reach those goals.
With divine intervention, God intentionally made the universe in such a way that life would be possible--he set all the conditions just right, so that just as the properties of matter make possible the creation of a jet aircraft, the possibility of life was possible (e.g., amino acids can form proteins).
Any of these can be combined with either emergent or reductive Being, giving six options in total: 1) emergent cause-and-effect, 2) reductive cause-and-effect, 3) emergent teleology, 4) reductive teleology, 5) emergent divine intervention, 6) reductive divine intervention.
In option 1 (emergent cause-and-effect), the universe would be start out strictly physical, until the appearance of consciousness, at which point it would then be physical and mental. This possibility has been alluded to above (e.g., in the paragraph on emergence). If successful, it would be compatible with current evolutionary theory (for the physical stage), and irreducible consciousness (as an emergent quality of complex matter). But it would still have to account for exactly how a type of complex organism is inseparable from its own specific type of consciousness. And even then, the emergence of consciousness remains an unintelligible brute fact: "essentially mysterious." Basically, matter just randomly developed to the point where it was somehow able to 'link up' with consciousness. There's no explanation for why this was likely, or even possible.
Materialism is actually one form of option 2 (reductive cause-and-effect). Everything is reducible to matter, and the possibility of life is present in the physical and chemical laws of cause-and-effect. So, if we simply add 'mind' into the equation, this one is the least radical option--it has the most in common with the current orthodox opinion. In this type of monism or panpsychism, everything is reducible to proto-mental elements (physical/mental 'stuff'), and the possibility of conscious beings is present in the laws that regulate this stuff. Just as the fundamental properties of matter make possible the formation of atoms, molecules, galaxies, etc., it makes sense to believe that the tendency for the development of conscious organisms was also there at the beginning, in these proto-mental bits.
Panpsychism has some interesting implications. We know from our own experience that consciousness is both active and passive. We passively take in impressions/perceptions/sensations and actively direct behavior (e.g., vision, which can be both passive, and actively directed). Proto-mental bits would also need to have active and passive components. In other words, this would imply some kind of active behavior on the part of these elements. And there would be an unbreakable connection between any mental and physical phenomenon: "one cannot have the mental without the physical aspect, or vice versa." So, a visual system would necessarily have 'visual experience' tied to it. And because it would have both passive and active features (i.e., the ability to direct actions), this would undoubtedly have a survival advantage. So consciousness would play a direct role in evolution.
This option has its own problems, however. It may seek "a deeper and more cosmically unified explanation of consciousness than an emergent theory, but at the cost of greater obscurity." It's easy and natural to see how the physical elements of the universe make up the more complex parts (atoms, molecules, cells, organs, planets, suns, etc.). But it's hard to imagine how proto-mental bits would combine to make more complex forms of consciousness. We propose that they exist simply because we need them to exist in order to make sense of anything, but apart from that, they're still a mystery. We can't detect them, predict how they interact, or understand how mental elements make up mental states (the way atoms make up molecules).
Another problem has to do with how it answers the historical question (Becoming). Going back to vision, even if the visual system is somehow implied in its parts (i.e., passive impressions, active behavior), it doesn't explain why it formed in the first place. Just like the standard evolutionary account, it can't explain how these organisms came to be, how sufficient genetic variations came to be. The question is the same as it was with matter: what is it about proto-mental bits that makes the appearance of life and conscious beings any more likely? Let's say we have these proto-mental bits. Why didn't they just remain proto-mental bits? Why did they combine into complex forms and thus create conscious beings? At this point, unless some serious advances are made in the future, 'proto-mental bits' make the world no more intelligible than it already is. It's even more speculative than evolutionary theory, because it adds something completely unknown to the basic substance of the world.
These problems make the intentional and teleological alternatives s lot more attractive. If we take the divine intervention options, for example, God could have created the world in such a way that the proto-mental parts would inevitably combine in certain ways, like a divine clockmaker setting things in motion. He could have assembled DNA or simply created beings of proto-mental parts. But if we want a secular theory, there are only two options. First, simply take the clockmaker out of the equation. Instead of God creating the perfect conditions, the universe just happens to have the perfect conditions so that physical laws give rise to organisms. Cause and effect. But we've seen the problems with this. That leaves us with the second alternative: teleological laws. These laws would govern change over time and tend toward certain outcomes over others. Contemporary science excludes purpose and goals in nature a priori--natural selection is based on chance, after all, and it's hard to think of goals without also having a being whose purposes are being fulfilled. But Nagel is convinced that teleology can be coherent and natural (without any reference to God directing things according to His whims): "natural teleology would mean that the universe is rationally governed in more than one way--not only through the universal … laws of physics that underlie [cause and effect] but also through principles which imply that things happen because they are on a path that leads toward certain outcomes--notably, the existence of living, and ultimately of conscious, organisms."
All the above was to try to account for basic consciousness: the experience of being alive, sensing, perceiving, moving, feeling, etc. But there's something else that needs to be accounted for: the fact that human consciousness is active in both thought and deed. That is, we have intentionality, "the capacity of the mind to represent the world and its own aims." Nagel thinks this active quality is only possible with a foundation of consciousness, and that it poses an additional stumbling block for materialism and theories that just focus on consciousness: "I believe that the role of consciousness in the survival of organisms is inseparable from intentionality: inseparable from perception, belief, desire, and action, and finally from reason."
