not altogether persuasive that, in the end, his theory really does go beyond the materialism he eschews.

Chapter 5 takes up the distinction between cognition and consciousness. Cognition is simply sensation, a basic awareness of encountered objects (this is a red book); consciousness is perception about things at a deeper level. In the act of perception the subject is engaged not only in a phenomenological task, but in an activity that stems from his or her psychology. The first order experience of the red book proceeds to a second order judgment about that experience (“I am having an experience or sensation of something red”). Finally, human consciousness has the capacity to reflect on the meaning of experiences for the subject (“Sensations are mysterious.”) in a third order judgment. Not everyone who sees a red book will likely attribute the same meaning to that experience at this more personal reflective level. Sam’s conclusion, “Red is marvelous—my favorite color,” will not be congruent with Shana’s “My favorite childhood book was red.” Consciousness appears to function uniquely to determine for the particular individual what the ultimate content of experience will be for him or for her.

The concepts addressed here are by no means simple; they require the reader’s careful attention, and often some rereading, to avoid losing the thread of the argument. Yet the author’s dedication to thoroughness demands a rigorous pursuit of the arguments that support his thesis, as well as the disposal of counterarguments. It is not surprising, then, that the brunt of the latter portion of this chapter and others is given over to answering the arguments that could be mounted against his conclusions. Asterisks abound.

The coherence between cognition and consciousness, grounded in a set of psychological laws governing the relationship between consciousness and physically demonstrable systems, is the basis for the author’s theory. The exposition of this connection considers the strong link between consciousness and cognition: persons’ judgments that experience occurs appear to be connected to real experiences. If persons are asked what they perceive, their answers will provide reliable crumbs pointing the trail toward the nature of consciousness.

The direct correlation between coherence and cognition does not deny that it is possible to ignore what is perceived and thereby to be unaware of what is available in the nexus of an experience. This objection, however, does not negate Chalmers’ hypothesis. Experience that persons can access data but in fact do not does not mean that a particular experience is not available to them. Further, it is also possible to be conscious of something that is not immediately present to observation. I am aware of my coat lying on the seat of my car, even though I am currently standing in the kitchen; I know who is currently president of the United States, although neither he nor accessible proof of that statement are available to me at the precise moment I make that statement.

The author finds parallels between what he proposes and contemporary scientific theories, particularly in the field of physics. He suggests that his theory, like some in physics, should be simple enough to be printed out on the front of a T- shirt—an interesting idea! His humorous asides consistently lighten the task for the persistent reader. As in earlier chapters, he sets forth his position and its alternatives and carefully eliminates the alternatives.

Where does the evidence to support his proposed “laws” originate? The author suggests the use of empirical data, gathered through the rather ordinary means of simply asking people about their own experiences. He understands that this methodology does not fully conform to the pure and rigorous model that characterizes scientific inquiry, but he believes it is sufficient for his purposes. His hypothesis, then, is: Where there is consciousness, there is awareness.

Even given its limits as a scientific process, Chalmers considers his theory useful as a pre-experimental basis for scientific inquiry into facts about experience. Every scientific investigation begins with some axiom. Used as such, Chalmers’ theory bridges the gap to the physical components of knowledge about experience, even when they are not made explicit. Essentially this chapter details more fully what he has presented earlier in the book.

In the third major division of the book (chapters 6, 7, and 8) the reader finds the meat of the author’s “positive theory of consciousness,” in its coherence to cognition. Besides using empirical evidence, the author explores principles of plausibility, simplicity, and aesthetics. He advances what he calls “the principle of organizational invariance.” Identical systems will process data in identical ways with predictably similar results. Within an entity, one can theoretically substitute one medium of information transfer for another (computer chips for neurons, for example) and expect the same results. The key is to replace the medium but to preserve the systematic interconnection of the elements.

With the groundwork laid, the author can move to the conclusion that, in theory at least, beings other than human persons have the potential for consciousness. If there is a cognitive and cohesive system present, it is logical to infer that such a system would be conscious. He believes, for example, that a computer could be constructed that would be aware of its own activity. This extension of the author’s thesis may ultimately call into question his dualistic notion of consciousness and reduce it to materialism after all. The author does not seem to think so, however. In essence, the imaginary HAL lives, a logical extension of Chalmers’ conclusion. The instances of such entities, those who could function as true agents or persons, is expected to be small, however. The exposition of the theory ends with a list of open questions.

The final chapters (9 and 10) are what the author calls his “dessert.” In them he offers applications of his theory to central questions in the foundations of artificial intelligence and quantum mechanics. He argues the case for the aggressive computer technology that might give rise to the conscious mind, which he had mentioned earlier. He makes some connections to the field of quantum mechanics.

Chalmers has written a dense and lengthy work to thoroughly cover the subject in a systematic manner. He has rendered a difficult and obtuse body of material almost accessible. Footnotes enhance the text with rich auxiliary information and cogent alternative arguments. The reading is made easier by the author’s sense of whimsy and his good use of examples. Cartoon characters (such as Calvin and Hobbes), zombies, and robots march across the pages to exemplify the author’s ideas. Following his use of black-eyed pea salad as an illustration to make a point, for example, the author offers a footnote with the recipe for the dish, a tasty reward for the persistent reader who has the courage to investigate the scholarly apparatus at the end of the text.

The book claims to target a popular audience, even identifying the “harder,” more technical portions to accommodate them, as noted above. The unsophisticated reader, however, will have to struggle mightily; the book is not at all the pulp equivalent of easy-listening music heard in the dentist’s office. While it can be conquered, success will come only at the price of some patience and effort. The question for one who does not share Chalmers’ burning desire to solve the nature of consciousness is whether the battle is worth the effort. Readers who resonate with his passion, “in their bones,” will no doubt devour it greedily.

Sources for Further Study

Choice. XXXIV, December, 1996, p. 625.

Library Journal. CXXI, July, 1996, p. 119.

Nature. CCCLXXXI, May 9, 1996, p. 123.

New Scientist. CLI, August 31, 1996, p. 40.

The New York Times Book Review. CI, December 29, 1996, p. 22.

Science News. CXLIX, June 15, 1996, p. 370.

Time. CXLVII, March 25, 1996, p. 50.

The Times Literary Supplement. June 21, 1996, p. 3.