Since "consciousness" means many things to many people, let me first define my use of the term (which is necessarily solipsistic because my consciousness is the only one that I know about. You will have to see whether you agree that these properties describe your own experience of consciousness). My viewpoint focuses on consciousness in the sense of the mental processes or their contents of which we are immediately aware at any moment in time. When I sense the environment, particular aspects of the environmental energy become the objects of consciousness in a never-ending flux of sensations. Memories of past sensations, or imagined sensations, may also be brought or bring themselves into consciousness. Beyond sensations, I am also aware of a limited set of internal manipulations of the relationships between such sensations, such as thinking that, if I dropped this egg, it would spatter all over the floor and my shoes. This kind of immediate awareness of sensations and events is experienced as a vivid "switched-on" activity that is peculiar to oneself; it is only by imputation that we assume that it is experienced by other humans and perhaps by other species to some phylogenetic level.

What I do not mean by consciousness is the sum total of all the things that have ever come to my immediate awareness or the cumulated store of my memories. I also do not mean the sense of myself in the world, which I would designate as "self- consciousness", except in the particular case when that sense comes to my immediate awareness. In other words, I define self-consciousness as that fleeting part of consciousness when I am aware of some aspect of my own thinking processes, not the underlying structure of self which forms and guides my responses. Finally, I do not mean the parts of my mental processes that seem to operate as subconscious workings of the thinking or emotional processes. My experience is that these subconscious workings often deliver thoughts, feelings or problem solutions to my consciousness without my being aware of the process by which the results were generated. I may have to engage in a conscious reconstructive process to understand the logic by which I reached a certain solution or emotional response. Such experiences convince me that much of the workings of the mind are, thus, unconscious. Most of my memories are also unconscious at any given time, lying dormant until called into active status in the arena of consciousness.

Another aspect of mental processes that is often confused with consciousness is understanding, or knowing. Understanding how something works or what someone means by their speech or their writing is a process that typically involves consciousness, often a heightened sense of consciousness. But this is not to say that understanding is consciousness. If I lie on my back in a field on a clear day, I experience a vivid sense of being surrounded by blue sky. I am highly conscious of the enveloping blueness but I do not feel that I understand it in any deep sense. I am simply aware of it. I may think about its origin in the scattering of light from particles of air, and its similarity to the Wedgwood blue of the china, or I may not. I do not have to think about the blueness of the sky to be conscious of it; I simply revel in its blueness as a pure sensation (or 'raw feel', in Bertrand Russell's term).

So consciousness may exist without understanding. Whether understanding may exist without consciousness is a thorny question, however. My view is that if a computer had a full range of responses to an object or structural entity, the ability to manipulate it on a variety of levels and predict the outcomes of such manipulations, it would be fair to say that the computer had an understanding of the situation. For example, when Big Blue (the computer) beat Gary Kasparov in their latest chess match, he was astounded at the deep level of understanding that it seemed to exhibit of the strategy that he was employing. I would say that it is fair to describe its strategems as showing an understanding of the game of chess, but the attribution of consciousness to this process of understanding is more problematic. The criteria for attribution of consciousness are not yet clear

The Emergent Property of Consciousness

I regard consciousness, in this immediate sense, as a transcendent state of the activity of the brain. Some boundary state must be transcended for the activity to pass from being unconscious to becoming conscious. What is transcended for the activity to emerge into consciousness, we don't yet know, but there seems no reason to suppose that it transcends the activities of material entities such as neurons. Consciousness is often considered emergent in some deep sense, but the simple fact of being an activity or process imbues consciousness with evanescent qualities unlike the stable properties of material objects. It is important to draw this distinction between object properties, like liquidity or redness, and the dynamic quality of an activity such as the flying of a bird or the operation of a computer algorithm, which I regard as a better analogy to consciousness. Consciousness is too often characterized as a simple property or quality attached to thought processes whereas it is more probably a dynamic aspect inherent to the process.

The computer algorithm is a revealing example. The distinction is often drawn between the computer algorithm and the hardware that implements it, but there is a deeper distinction between the algorithm as a concept and the algorithm as a process. AS a concept, the algorithm can be conceived and constructed in computer code, stored either as written symbols or as memory instructions in the computer. But when the computer is activated, the algorithm runs and produces its expected (or unexpected!) results. The conceptual algorithm has become a process, actually doing what it was designed to do as a dynamic operation rather than a static set of instructions.

In respect to its transcendent quality, consciousness seems more akin to cooperative processes such as fire, lightning, waves, tornadoes or nuclear reactions. In each case, a background level of activity intensifies into a self-organizing state that transcends the original activity state. For fire, the transcendent state is the colored region of the flame where the chemical recombination actually takes place. For lightning, it is the discharge of the accumulated electrical charge in a path connecting the cloud to the ground. For waves, it is the break-out of the wave into the foam of the surf. For nuclear reactions, it is the acceleration of the chain reaction into a nuclear explosion, when the increased energy transcends the bonds that hold the core material together.

The tornado is a particularly appealing example, where wind currents that merely blow particles across the earth's surface intensify into a self-organizing funnel that can suck large objects up into the clouds. This transformation characterizes the sense that I intend for "transcendence" in a physical process. It is the dynamics of the process that form the wind currents into the coherent entity of the tornado, which then develops the emergent power to levitate objects. The process is self-organizing, developing from the eddy currents of wind blowing past static objects in the environment.

The Structure of Consciousness

What do I mean by the "structure of consciousness"? Is human consciousness more like lightning, where the entire cloud discharges through a single pathway, or more like fire, where many elements can contribute to the flame simultaneously? In other words, is consciousness a unitary local process in the brain, scanning through a range of sensory inputs and memory contents by a rapid serial process, or is it a parallel distributed process, able to integrate the signals from many sources simultaneously?

This is not a new question: it has been addressed in the guise of studies of attention for decades. Now, attention is similar to but somehow distinct from consciousness. In my view, the difference between them is a relativistic one: attention describes the flow of mental traffic in relation to the highway architecture, consciousness is what it is like to be in the car driving through the traffic ahead. Thus, the reason that consciousness has an experiential quality unlike any other process that I observe is that I am the process of my brain, and being conscious is what it is like to be a process. The dramatic transformations that occur in the theory of relativity with a switch in reference frame from outside observer to the light-speed traveler give some insight into the power of a relativistic transformation to change the apparent properties of a process. Without an appreciation this power, no simple claim that consciousness is incomprehensible as a physical property can be evaluated.