Oxford University Press (1996) ISBN 0-19-510553-2
This book is perhaps most remembered for its attack on mainstream thinking on consciousness. However, the bulk of the work is taken up in trying to establish Chalmers own theory of consciousness, which after all turns out to be not that distant from conventional ideas, although characterised by a quirky view of the role of information.
In the introduction, Chalmers coins the expression that this book has become famous for, referring to consciousness as the ‘hard problem’. At this stage, he states the basic conundrum that while most evidence points to consciousness arising from brains, it is not clear how a physical structure such as the brain could have subjective experience, nor why it is like something to be a brain system. He contrasts the fact that we have a more direct experience of consciousness than anything else, with the fact that scientifically we understand the non-conscious aspects of the universe much better than consciousness. In fact, the grounds for our belief in consciousness derive solely from our experience of it. A non-conscious entity that had not experienced consciousness would not derive the idea from the physical facts of the universe.
Chalmers attacks many other consciousness books for addressing subjects such as information processing and reporting of internal states, rather than the hard problem of consciousness itself. In these books, the question of the inner subjective life is either pushed to one side, or even declared answered, without really having been discussed. He highlights the common trick of redefining consciousness as something else, such as particular cognitive functions, explaining these, and declaring the problem solved. He criticises other writers for merely explaining this functional aspect of consciousness or in other cases explaining self-consciousness, and trying to treat that as if it were the whole of consciousness. He calls on his peers to face up to the problems that make consciousness difficult, and to take consciousness seriously.
He says that he has ‘little idea’ what the proposition that consciousness is an illusion could mean, since the existence of our conscious experience is more certain than any other aspect of our existence. He deems any call for proof of consciousness inappropriate, because we know about consciousness more directly than anything else.
Chalmers also makes a very apposite observation about the position of science relative to consciousness. He says that in this book, he will take science seriously, in the sense that he will not dispute established scientific theories, but that he will not feel constrained in areas where scientific opinion is as ungrounded as anyone else’s. This is an extremely important distinction, since all too often in consciousness studies, scientists, philosophers and other writers who choose to speak for science, make metaphysical claims, and advance theories unsupported by experiment or observation, apparently assuming that these have the same authority as established scientific theories, because they are endowed with some notionally ‘scientific’ tag. Chalmers says that his ideas are compatible with science but not necessarily fashionable with contemporary scientists.He discusses the nature of reductive explanations in science. These involve a description of how particular functions are performed. For instance, once we have described how the functions of reproduction are performed, we have explained reproduction. There is no overriding reproduction idea requiring further explanation. Reductive explanations work well in cognitive science. Thus, while many details may not be understood, it is possible to outline how the function of learning is performed by the brain, and this gives us a satisfactory reductive explanation of learning.However, although reductive explanation work well with brain functions, they break down with phenomenal consciousness. The difference here is that while systems such as reproduction and learning can be described by how these functions get performed, consciousness cannot. Even if we accept a causal role for consciousness, it is still not defined by any causal role, but by its quality of subjective experience. If consciousness accompanies the performance of a function, a description of a function does not entail an explanation of why consciousness is present.Physical explanation is seen as coming down to the explanation of structure and function. This works well for the brain and its processing, but it does not work well for consciousness which is not explained by the other structures and functions of the brain. The fact that consciousness accompanies some brain processes is a further fact, in addition to the functioning of the processes. Chalmers claimed that the then current models of consciousness only explained functions such as reportability or attention, but said nothing about why these are accompanied by subjective experience. This is the case with Baars global work space, where there is no explanation of why the information in the global work space should be conscious. Similarly, Edelman has developed theories of processing related to re-entrant connections between cortex and thalamus, but gives no reason why such processes should give rise to subjective experience.Dennett in particular pressures people to believe that brain function equates to consciousness, but never gives a reason. The link between the psychological and the phenomenal is simply assumed in his work. Chalmers argues that Dennett’s dismissal of consciousness rests on an ambiguity in respect of the word ‘seems’. This can refer to phenomenal experience, but can also refer to a subject being disposed to make a particular judgement. Dennett has a theory for reportability and argues that this explains consciousness. Chalmers, however, argues that this reportability only refers to the disposition to make a judgement and not to any phenomenal experience.
Consciousness is seen as a primitive. Attempts to define consciousness in terms of something else prove futile. The best Chalmers himself feels he can attempt is to refer to ‘the subjective quality of experiencing’. Experience involves phenomenal qualities or qualia. He regards this subjective quality as something unexpected, something that would not have been forecast just from the basis of our scientific knowledge of the non-conscious world. He also says that there is something it is like to be a conscious being, while by contrast it is not like anything to be a non-conscious object.
However, in addition to the raw qualia or subjective quality of the colour red, cognitive processes such as thinking and eventually acting also have a subjective quality. Chalmers also criticises the attempt during much of the 20th century to subsume phenomenal experience into the mere psychological processing leading to the production of behaviour. In an experience of colour, the relevant topic is what the colour feels like, rather than its effect on subsequent behaviour.
The Hard Problem:
Chalmers divides the mind-body problem into two. Explaining the processing of the brain is an enormously complicated process, but in principle it should yield to existing research approaches. It is not really an easy problem, but it is easy compared to explaining phenomenal consciousness, for which it is not clear what sort of research approach should be follow. The stimulation, processing and responses of the brain are often accompanied by subjective experience, but is not clear how this links with the physical structure of the brain.
Chalmers defines psychological properties as the processing in the brain that is likely to influence behaviour. This is the processing which constitutes the ‘easy’ part of the mind-body problem. Functions such as attention and voluntary control involve consciousness, but can be described in terms of cognitive processing, which lies within the ‘easy problem’ sector.
Chalmers thinks that subjective experience can be linked to brain processing through the state known as awareness. He wishes to regard this as a psychological property associated with subjective experience. He quotes another writer, Newall (1992)(1.) as defining awareness as ‘the ability of a subject to make its behaviour depend on some knowledge.’ Chalmers himself takes the example of the phenomenal experience of pain leading to physical withdrawal from the source of pain. This could sometimes involve a non-conscious reflex, but in this case Chalmers appears to be thinking in terms of a slower or more considered withdrawal from harm. Chalmers also quotes Block(2.) who refers to access consciousness which is very similar to Chalmer’s idea of awareness. Access consciousness has content that is poised for use in reasoning and beyond that in conscious control of action and speech. Chalmers excludes from his particular definition of awareness, being aware that Paris is the capital of France, which may just be stored in the memory, and only occasionally come into consciousness. Awareness would thus seem to be defined as consciousness that impacts psychological processing and affects behaviour. Chalmers appears to make a distinction between awareness or access consciousness where the subject is consciousness but using consciousness as part of processing and subsequent response and actions, from the more difficult to explain phenomenal consciousness.
Another central plank of Chalmer’s approach to consciousness is the concept of supervenience. This is related to the idea that one set of facts can fully determine another set of facts. The second set supervenes on the first set. As an example, physical facts determine biological facts, so biological facts supervene on physical facts. Higher-level properties supervene on lower-level properties, which are also seen as more fundamental.
For the purposes of consciousness studies, supervenience can be divided into logical or conceptual supervenience and natural supervenience. Logical or conceptual supervenience applies to anything that could be conceived in any hypothetical world. This refers to the physically possible, but excludes the paradoxical. Thus flying telephones are logically supervenient, but male vixens are not.
Natural supervenience is slightly weaker than logical supervenience, since it only applies assuming that laws of physics etc. hold. In a hypothetical universe with different physical laws, a particular supervenience might not apply. Chalmers takes the view that consciousness is naturally but not logically supervenient on physical properties. The fact of being only naturally and not logically supervenient means that our world requires a law or laws to apply to make consciousness derive from or be supervenient on physical properties.
Conscious experience is claimed to arise from the physical properties of an organism as a result of certain laws of nature. Consciousness is not in itself physical, hence the expression ‘property dualism’, although it derives from and depends on physical properties. In developing this theory of consciousness, Chalmers stresses the close ties between consciousness and cognition. Thus green perceptions and green phenomenal experience are closely connected. He sees consciousness and cognition as being linked by phenomenal judgements, but just explaining judgements about consciousness is not enough to explain consciousness. We do not just judge that we have conscious experiences, we know that we have conscious experiences.
The cornerstone of Chalmers theory is a set of laws governing the relationship between consciousness and physical systems. The laws must show how consciousness supervenes on the physical. The relationship is seen as needing to be systematic and the consequence of underlying laws. Chalmers points out that consciousness and psychological processing leading to behaviour are systematically related. There is a reliable or usually true relationship between conscious experience and actual processing. In particular, consciousness is closely related to Chalmers restricted form of awareness, such as consciousness of pain leading to withdrawal from the source of harm.
Chalmers speaks of structural features in consciousness corresponding to structural features in awareness. With colour vision, it can be argued that one person’s experience of red may be entirely different from another’s, but if these subjects have normal colour vision, they will agree that there is a difference between two colours, such as red and green. This is seen as constituting a difference structure in conscious experience. The same sort of structures apply in other modalities. Subjective experience is ineffable, but the relationship between subjective experiences is not. This structure or geometry in consciousness is mirrored in awareness. An account of visual processing is argued to give an indirect account of the structure (say the relation between red and green) in phenomenal experience. Chalmers views the coherence between consciousness and awareness as a bridging principle to the physical world. He further suggests that the coherence between the two is a law of nature. Consciousness is here said to arise because of the functional organisation associated with awareness.
At the end of the day, it may be hard to find Chalmers argument very convincing. A lot rests on what might be thought to be a play of words in the distinction between awareness and consciousness. If we put aside for the moment the widespread mainstream view that consciousness has no causal effect, we could accept Chalmers view that there is a part of consciousness concerned with immediate behaviour, for instance a non-reflex withdrawal from a source of harm, and that there is a correlation between this action and the experience of pain. As a subjective experience, this is the same sort of thing as the subjective experience of the colour green, which itself may not have any particularly direct link to immediate behaviour. However, none of this gets us away from the essential problem of why do we have subjective experience of any of this, and why don’t we deal with functions such as withdrawing from harm only through non-conscious processes.
Chalmers information theory:
In the last part of his book, Chalmers links his awareness/consciousness coherence theory to a theory based on information. He draws on the ideas of Shannon in the mid 20th century. The most basic sort of information is the bit, representing the choice between two possibilities. A state that exists within a range of possibilities has a specific meaning. This gives rise to the concept of an information space. There are relations of difference between information spaces. Complex information can be built up from simple information as in a series of 0s and 1s. Information spaces are viewed as an abstraction, but are realised in the physical world in systems as simple as an On/Off switch. Information is seen as something that can always be transmitted, often by means of light, and therefore it is viewed as being part of a causal pathway. Information is seen as being embedded or instantiated in the physical world.
Phenomenal experience can certainly be seen as a form of information. The pattern of differences between experiences, say between the colour experiences of blue, red and green can comprise information. Chalmers highlights the fact that information, such as pulses of red light, realised phenomenally, is also realised physically, and there is a close coherence here. He describes this as information leading a double life and suggests that it is information that provides the link between the physical world and consciousness. There is a phenomenal state and an information state.
This theory of information only seems to serve to deepen the explanatory gap that seemed apparent in the consciousness/awareness argument. The physical basis of information storage and transmission is a well understood part of the physical world. It is not clear why the property of consciousness should suddenly be attached to it. Certainly, information processing and consciousness are connected in the brain, but so are many other physical properties and processes. The old question that opposes so many consciousness theories, ‘why should this produce consciousness?’ arises here too.
Chalmers does not help his argument by introducing the rather fantastic notion that information processing machines right down to the humble level of thermostats possess some element of consciousness. Chalmers suggests there is a simple sliding scale from the human mind through various animal minds to the level of computer minds and finally thermostat minds. This scale seems to ignore an important functional difference between machines and at least the higher animal minds, which is the impact of the experience of emotion, as physically instantiated in the limbic system, on the preference for one course of action over another. Emotion is in fact hardly mentioned in Chalmers book, and this reminds us that this is after all a book of the 20th century, during most of which the mention of emotion was almost as taboo as the mention of consciousness in scientific circles.