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The experience of consciousness seems incommunicable and ineffable. Yet science can hope to explain how it arises

The question: Can science explain everything?

When Andrew Brown first posed this week's question to me he asked "Can science describe everything?". My instant, unreflective reply was "No". He implied that this might be a less restrictive question than "Can science explain everything" and yet my instant reaction to this one was "Yes". I'd like to explore this curious difference.

Science can (potentially at least) explain everything because its ways of trying to understand the universe by asking questions of it should not leave any areas off-limits. The methods of openness, inquiry, curiosity, theory building, hypothesis testing and so on can be adapted and developed to explore and try to explain anything.

But what is "everything"? I look out of my window and see green trees and grass and grazing cows, a river, a pond, birds, sky, clouds …. but everything? This is where description becomes so hard. There is just so much stuff in the universe and it's all so complicated. Let me give two examples, a simpler one and a really tough one.

Let's take those cows, or my black and white cat lying here on a comfy chair. There's no way we can even aspire to precisely describing every black and white pattern on every cow and cat in the world. There are billions of them and each is unique. Even if everybody in the world devoted themselves to the task, they could never capture them all. Yet we can explain how genetic information codes for the construction of pigments, and developmental variations lead to the individual patterns.

To take a second example, closer to my heart and my research, there's the "hard problem" of consciousness, of subjectivity, of private experiences, of "what it's like" to be me.

Here I am, sitting at my desk, experiencing all sorts of sounds, sights, touches and smells, but I cannot adequately describe them to anyone else. This is the very essence of subjective experience â€" that it seems to be private to me. To raise old philosophical conundrums, I cannot know whether my experience of the greenness of the grass is anything like yours. What if my green experience were like your beige, and your black and white like my mauve and purple? I cannot describe my sensations (or qualia) of greenness in any other way than to say "it looks green", implicitly comparing it with other colours in the world and using agreed names to do so. In this sense colour experiences (and smells, and noises, and tastes) are ineffable.

Ineffability is even more acute when we come to special states or transcendent experiences. What can I say, for example, about my spontaneous mystical experiences? That I became one with the universeWhat I saw another world that I like to be guided by something I can not describe or name? What can I say about the states I reached through meditation ? How could I see the nature of experience and look at the land of indescribable existence? What can I say about the deep states reached by taking LSD ? That the world was alive and flowing through me, that was not I? I can say all these things, and some people say "Oh yes, I know what it means". But we will probably agree that we have nothing to say, really reflects these experiences.

Science cannot describe these experiences, but will it ever? Those who think the hard problem is real claim that the nature of experience will always remain beyond the grasp of both description and explanation. But those who think it's a "hornswoggle problem", a "non-problem" or an illusion, argue that when we really understand the workings of the brain the hard problem will have gone the way of caloric fluid or the élan vital which was once sought so assiduously to explain the essence of life.

A subtler possibility is that we explain the ineffability itself. One example of this is a framework for thinkingof natural and artificial information processing systems developed Aaron Sloman and Ron Chrisley. They want to explain the "private, ineffable, it seems to us", explaining how and why the ineffability problems arise at all. Their virtual machine (architecture CogAff ) includes processes that classify its own internal states. Unlike words that describe common experiences (such as seeing red in the world) these refer to internal states or concepts that are strictly not comparable from one virtual machine to another â€" just like qualia. If people protest that there is "something missing"; the indefinable quality, the what it's like to be, or what zombies lack, their reply is that the fact that people think this way is what needs explaining, and can be explained in their model.

This and other competing theories suggest a new possibility â€" that conscious experiences may remain ineffable even when science thoroughly understands how and why. In this case I would be right in my intuition that science cannot describe everything but may well be able to explain that which it cannot describe.