FROM KEITH WARD, GRESHAM PROFESSOR OF DIVINITY AT GRESHAM COLLEGE : Consciousness is a major problem for materialists, who believe that everything that exists is composed of publicly observable material elements in this (or at least in some) space-time.
Yet consciousness is something that is most immediately known to each person who reads this post. It is immediate knowledge by acquaintance.
Empiricist philosophers may have been wrong about many things, but they were probably right in thinking that all knowledge begins with experience—with a direct apprehension of some state of affairs, which is then described and categorized using general concepts. If this is so, consciousness is the necessary basis of all theoretical knowledge, including knowledge of the human brain and its behavior. One problem philosophers have traditionally dealt with is whether and how such immediate acquaintance plus the conceptual interpretation can give rise to accurate theoretical knowledge of the world outside of conscious experience.
It is a strange inversion of this situation to say that the problem is how material brains can give rise to conscious experience. That inversion suggests that we know material brains exist, but consciousness may well be an illusion or a causally inert by-product of brains. Yet we only know that brains exist because we are conscious of them. If such consciousness is an illusion, then material brains are part of the illusion. There is no sensible way of saying that our consciousness is illusory but its contents are absolutely real. We have to trust that our consciousness provides genuine knowledge by acquaintance before we can trust that any of its contents provide clues to what is real.
But are brains not real? And does their functioning not govern the sorts of experiences, the sorts of consciousness, we have? Yes indeed, we learn—through experience and reflection upon it—that there are material causes of conscious states. But causes are logically distinct from their effects, and far from throwing doubt on the existence of those effects, a causal account presupposes that effects really exist.
Brain events do cause conscious states to exist. Is this a problem? Only if it is believed that material events can have only material effects. But that is a dogma that consciousness undermines. Consciousness seems to show that materialism is false, since consciousness does not consist of publicly observable material elements in space-time. There are material causes of immaterial states. Conscious states also usually involve an affective, evaluative element, and a tendency to seek or avoid their objects. So, in the absence of a conclusive rebuttal, it is reasonable to believe that conscious states influence behavior. It they did not, consciousness would have no evolutionary efficacy, and knowledge of a state of affairs would have no effect on behavior.
It is a basic datum of experience that our consciousness of a situation, of its pleasant or threatening character, will influence our behavior. Reading these words, for instance, will cause some responsive feeling and activity—if only an inclination to write a letter of protest or to think hard, which puts our brains into new physical states.
The major mystery of consciousness is just what the causal relationship between conscious and physical states is. There are six main possibilities: consciousness is an illusion (hard materialism), matter is an illusion (hard idealism), consciousness is dependent on matter (nonreductive physicalism), matter is dependent on consciousness (theism), the two exist independently (dualism), or they are different aspects of one underlying reality (monism). All have been tried, and none is wholly satisfactory. That is why consciousness is such a fascinating and important problem.
My own view, on strictly philosophical grounds, is that consciousness is an irreducible feature of reality and is probably the ontologically primary reality—which inclines me to views more like the last three on my list. The great majority of classical philosophers have taken this view. But to work it out fully, taking into account the recent findings of evolutionary biology, neurophysiology, and quantum physics, is a formidable undertaking, requiring both bold speculation and intellectual humility.
I agree with University of Oxford mathematician Roger Penrose in thinking that the future of science is closely bound up with somehow integrating consciousness and the material substratum of the cosmos in a coherent way. Neither of us, I think, suppose that it has yet been done.

Keith Ward appears with the Venerable Yifa, Susan Blackmore, Daniel Dennett, David Chalmers, John Searle, and Colin McGinn in "Why Is Consciousness So Mysterious?" the third episode in the Closer to Truth: Cosmos, Consciousness, God TV series, which airs Thursdays on the PBS HD network and many other PBS stations. Every Friday, participants in the series will share their views on the previous day's episode. Coming up next week: series host and creator Robert Lawrence Kuhn on "Did Our Universe Have a Beginning?"