Chapter 3 of Mind and Cosmos is simply titled, “Consciousness.” Here, Thomas Nagel seeks to lay out the complete case for his assertion that naturalism, materialism, reductionism, etc., cannot fully explain consciousness. He doesn’t define consciousness in this chapter, but he has written about it earlier in this book and in many other books and articles. When I think about the issues Nagel is raising, I find that I need a clear definition of consciousness before understanding very much of what he is saying.
The reason consciousness is such a difficult word is that there are so many perceptions of what it is. One extreme position is that consciousness doesn’t exist! Usually what is meant by the non-existence of consciousness is that it is an accidental byproduct of evolution, sort of like the color of blood. It is not a fundamental function; it simply emerges when physical organization becomes complex enough. However, there is no explanation as to why consciousness should emerge from complex function in the way that one can explain the color of blood from its composition.
One way that Nagel defines consciousness is in terms of subjective experience, such as our sense of taste or our experience of color. He has written elsewhere that we cannot be certain that other people experience the taste of chocolate the same way that we do. We can agree to name a certain taste “chocolate,” but we cannot really be sure that we each experience that taste in the same way. It is possible to extend the example of taste to other subjective experiences such as love, fear, pain, revulsion, shame, etc.
Once we consider the entire range of subjective experience, I think it is relatively easy to argue that such experience would develop naturally as a necessary attribute by natural selection. That reasoning might go like this: It is not only the individual that is important to evolution. The kinship group, tribe or other social grouping is also important because such groups ensure the survival of the individual. Groups can raise armies and provide for the common defense. Groups can help ensure that individual DNA gets passed on to the next generation, and so forth.
But groups require social cohesion. Groups don’t like individuals who don’t play well with others. In order for an individual to be a good member of a group, that individual must consider the sensibilities of others. The individual must develop empathy for others in order to understand why it might be wrong to take unfair advantage of other group members. As Nagel has written elsewhere, an understanding of one’s own subjective experience is necessary for empathy.
The memory of our own subjective experience requires consciousness. We must be able to focus our attention on experiences that cause feelings and remember them. He has also referred to this ability as mental capability or “mind.” The evolutionary reasoning alone seems to provide solid evidence for the reality of subjective experience and consciousness. It’s at least as real as any other objects of philosophical inquiry such as the existence of the external world. We cannot live successfully in the real world without a solid belief in the external world and the subjective experiences of ourselves and others.
So, if the case for evolution naturally explains the development of subjective experience and consciousness, what is missing? What is missing is the reductionist, scientific explanation that shows why subjective experience and consciousness arises from the physical aspects of evolution. Unlike the color of blood which can be explained in terms of its molecular composition, subjective experience has no obvious connection to the physical.
At this point one has to decide whether to consider dualist solutions to the problem. And Nagel gives a very good explanation of the history of proposed solutions. The problem begins with the nature of the post-enlightenment scientific revolution and he assigns a major role to René Descartes. Descartes’ major accomplishment was the discovery of analytic geometry: Descartes showed how geometry could be analyzed numerically. This development was essential for the later development by Newton of the laws of motion. Without analytic geometry, Newton could not have subjected motion to numerical analysis. This led to the development of calculus which laid the foundation of all modern scientific explanation.
However, Descartes is famous for something else. He thought deeply about consciousness and its connection to the nascent materialist explanations of the world. The new developments in science were possible because they set aside the experience of consciousness. A detailed, numerical description of the physical world became possible by leaving out any explanation of the mental world. Descartes attempted to include the mental world as an associated phenomenon of the material world without an explicit, physical connection. That is the source of his famous dictum, “Cogito ergo sum,” or “I think, therefore I am.” Descartes’ assertion means that mental phenomena and physical phenomena arise together; we would not know that we exist in a material sense without consciousness.
This explanation of consciousness by Descartes is known as Cartesian Dualism and it has been the source of ongoing controversy about the nature of the world. If one accepts dualism, then there is something other than matter in the universe and that something can be called spirit or soul or sometimes, “the ghost in the machine.” Therefore, dualism is the bane of those desiring a materialist explanation. And that includes Nagel.
But Nagel also shows how difficult it is to avoid dualism when all materialist explanations have failed. Those difficulties have challenged me. I will write about them next time.