It's Monday morning, and Mr. P steps out of his house, headed for the trolley that will take him to work. The air is still brisk, but as he strides down the sidewalk, rays of sunshine fall on his face. "How nice and warm!" he thinks, and he decides to walk the entire way to the office, even though it will take 10 minutes longer than the trolley. He makes a right turn and heads downtown.

Before he reaches the next corner, Mr. P has already forgotten the episode. To philosophers, however, such ordinary occurrences involve problems so extraordinary that they have wrestled with them for more than two centuries. Somehow the nerves in Mr. P's skin and the neurons in his brain registered the sun shining on his face as a feeling he experienced as "pleasant," and that sensation prompted him to take a sudden, deliberate action. Everyone knows what this chain of events feels like. But no one knows the exact connection between simple neuron activity, our subjective response to it and the exercise of our free will. Are the neural activity and the sensation of "pleasant" ultimately one and the same, or does the conscious feeling arise as a secondary effect of the nerve activity?

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