 The opposite position, monism, says there is only one kind of stuff, brain, and the sensations like the red of a tomato simply represent the pattern of activation of certain brain cells.Many people find this simple monism unsatisfactory, though, because it does not really deal with the fact that the red of a tomato and a pattern of activation in region V4 of the visual system seem so very different.Bridging that difference is what neuroscience calls "the hard problem."