"Everyone knows what consciousness is: It is what abandons you every evening when you fall asleep and reappears the next morning when you wake up." (Edelman, 2000: 1)

Explaining consciousness is not so easy: it has been a central problem for both philosophy and psychology over the centuries. Dualists such as Rene Descartes recognised the difficulty in defining the relationship between mind (soul for Descartes) and body. He valued the notion of consciousness, coining the dictum Cogito ergo sum - 'I think, therefore I am.' Descartes boldly (and wrongly) identified the pineal gland as the seat of the soul, stating in his The Passions of the Soul that 'This gland is variously affected by the soul ... it impels the spirits which surround it towards the pores of the brain, which discharge them by means of the nerves upon the muscles.' (cited in Murphy, 1949: 19).

'Consciousness remains a mystery' says Susan Blackmore in the first chapter of her book Consciousness: An Introduction (2003: 7) despite our rapidly expanding knowledge of how the brain works. She goes on to reflect on the fact that whereas many old philosophical problems have been resolved (or have become irrelevant) as science developed, the problem of consciousness continues to be difficult:

"In essence it is this. Whichever way we wriggle out of it, in our everyday language or in our scientific and philosophical thinking, we seem to end up with some impossible dualism. Whether it is spirit and matter, or mind and brain; whether it is inner and outer, or subjective and objective, we seem to end up talking about two incompatible kinds of stuff." (p.8).

Christof Koch (2004: 1) poses the fundamental mind-brain question in this way:

"... what is the relationship between the conscious mind and the electro-chemical interactions in the body that give rise to it?"

Consciousness is a private matter - no one else knows what it is that we experience within our inner selves. Koch elaborates (p.4):

"A sensation cannot be directly conveyed to somebody else but is usually circumscribed in terms of other experiences. Try to explain your experience of seeing red. You'll end up relating it to other percepts, such as 'red as a sunset' or 'red as a Chinese flag' (this task becomes next to impossible when communicating to a person blind from birth). You can talk meaningfully about the relationships among different experiences but not about any single one. This too needs to be explained."

Blackmore (p. 9) observes that  William James  held consciousness to be at the heart of his psychology but also recognised that consciousness could be abolished through brain injury. William James regarded Psychology as an integrated science of mental life and described the seemingly ever-changing flow of ideas, feelings and images as a 'stream of consciousness':

Edelman (2000: 6) finds that scientists have had as much difficulty as philosophers in dealing with the problem of consciousness:

"If we look at psychology, we find that the 'science of the mind' always had trouble in accommodating what should be its central topic - consciousness - within an aceptable framework. The introspectionist tradition of Titchener and Külpe was the psychological counterpart of idealistic or phenomenonological positions in philosophy; it attempted to describe consciousness viewed by the individual exclusively from the inside, hence the term introspection. (...) By contrast, behaviorists notoriously attempted to eliminate consciousness completely from scientific discourse (...)"

References

Blackmore, S. (2003) Consciousness: An Introduction, Oxford University Press

Edelman, G.M. and Tonomi, G. (2000) A Universe of Consciousness: How Matter Becomes Imagination, Perseus Books Group

Koch, C. (2004) The Quest for Consciousness: A Neurobiological Approach, Roberts and Co.

Murphy, G. (1949) An Historical Introduction to Modern Psychology, 5th edition, Routledge & Keegan Paul: London.