"Consciousness," writes the American philosopher Daniel Dennett, "is just about the last surviving mystery." Many people find such statements perplexing. Surely consciousness is produced by the brain, isn't it? Though this seems obvious to those who have never studied the subject, the reality is more complicated. The strange thing about consciousness is that the more intensely you study it, the harder it is to explain.
What do people mean by the word consciousness? At the simplest level, consciousness means being awake and aware, able to process information and respond to external stimuli. But consciousness also means subjectivity, or the feeling that you are a self, an "I" who thinks your thoughts and recalls your memories. This is where being conscious is different to having a mind. Your dog has a mind, but though he is conscious at the simplest level (able to process information and respond to external stimuli), it is doubtful that he is conscious quite in the way you are. A dog or horse is not conscious of its consciousness, not aware of being aware. Put another way, they are not aware of themselves "in here" having their thoughts and experiences.
Take a book from your shelves. Hold it in your hands and be conscious of the weight and texture. Now look at the color. Is it dark green or light brown? How does the book smell? Does it have that distinctive, fusty smell of an old book, or the clean, fresh smell of a new one? Now consider your experience of the book. How do you know that a friend or neighbor experiences books in the same way? You may believe they do but you can never be sure. Consciousness is your private experience, one that no one else can ever know.
Pick the book up again. Ponder your subjective experience a little deeper and you will soon hit upon what the philosopher David Chalmers has labelled "the hard problem." Chalmers means bridging the gap between an inner, subjective world of experience and an outer, objective world of physical books. How did a physical, material universe of atoms, molecules, cells, and brains lead to unique, private, subjective experiences like the one you had when you held and smelt that book? No matter how much knowledge scientists accumulate about the grey lump of goo inside your skull, they cannot bring these subjective and objective worlds together. They just seem too different.
In the 17th Century, the French philosopher Rene Descartes argued that there were two kinds of stuff in the universe, mind and matter. When you look out of your window, you see what he called "res extensa," or "extended substance." And this, according to Descartes, includes your body. He named the mind, or soul, "res cogitans," or "thinking substance." This view is known as Cartesian dualism and hangs like a shadow over all discussion on the subject.
In general, scientists are materialists who seek to explain everything in terms of matter and energy. And most would reject Descartes' belief that consciousness is composed of some special, unique "substance." Over the years, many different materialist explanations have been offered. For example, Professors Crick and Koch suggested that consciousness could be traced to the brain's pre-frontal cortex. The physicist Roger Penrose has even argued that human consciousness originates in the wave functions of quantum particles.
Materialists generally agree that matter precedes consciousness. In other words, conscious minds depend on matter. First you have the "big bang", then atoms and energy and, eventually, the emergence of life. Through evolution, brains and nervous systems evolve and consciousness appears. In other words, consciousness emerges from a particular organisation of matter. If life were to be destroyed, these brains and nervous systems would disappear from the universe, taking consciousness with them.
One of the most famous materialist explanations was proposed by the English biologist T.H. Huxley, friend and defender of Charles Darwin and grandfather of the novelist Aldous Huxley. For Huxley, the relationship between consciousness and the body resembled that between steam and the train which produced it. Consciousness, in Huxley's opinion, could no more affect the human body than steam could affect the trains that puffed across 19th century England.
Though most scientists and philosophers are materialists, many are not. And numerous non-material, or mystical, explanations have been offered. Whereas the materialist argues that matter precedes consciousness, and that consciousness somehow emerges out of matter, some have argued the opposite: that consciousness is fundamental and precedes matter.
The American philosopher and psychologist Ken Wilber, for example, supports the non-materialist view of consciousness. Wilber encourages people to experience this for themselves. Sit cross-legged in meditation. Become aware of the objects in the room, the sounds and colors and so on. Now say to yourself "I am conscious of such things, but I am not those things." Next, become aware of your body and repeat to yourself "I am conscious of my body, but I am not my body." Finally, become aware of the thoughts, images, and memories that pass through your mind. Now say "I have these thoughts, memories, and images, but I am not these things." In this way, you soon reach what Wilber refers to as "the witness," meaning the basic conscious awareness 'beneath' or 'behind' not just physical objects but emotions, thoughts, and memories. Such things are objects in your awareness. Only the witness itself can never become an object. You cannot witness the witness, or be conscious of your consciousness. This witnessing consciousness, argues Wilber, is a "vast emptiness" outside of space and time; it is the clearing or empty space through which "the limited, bound, mortal, and finite objects parade by in the world of time." In other words, consciousness is fundamental.
The British physicist John Wren-Lewis left a fascinating account of such an experience. After falling into a near-fatal coma, Lewis found that his consciousness had undergone a radical shift. He became aware that what he had previously taken to be his subjective experience of the world was in fact a delusion. His old sense of self, or 'ego', had disintegrated and he had awoken to the true nature of consciousness, to what he called "eternity consciousness." In comparison, his previous life now seemed like a waking dream. He had assumed that his consciousness was separate and distinct from other consciousnesses. Now, through what a Buddhist would call "enlightenment," he had grasped that that was a delusion.
Of course, many dismiss such views. They would argue that such experiences cannot be presented as evidence. Science is founded upon facts, not personal experiences.
Consciousness both fascinates and bewilders philosophers and scientists. The fact that it still cannot be explained infuriates some and thrills others. Perhaps most exciting of all is the fact that what Dennet calls "the last surviving mystery" is your experience itself!