2013 ). The disagreement between dualists and physicalists is the present status of
the hard problem.
Philosophers have gathered a constellation of thought experiments that are
designed to illustrate the puzzles of phenomenal experience and to reveal the
contrast between these and any possible neurological knowledge. Examples are:
- The inverted spectrum problem. I know what a red visual image feels like to me,
but how do I know that your visual image of redness does notlook to youlike
my visual image of greenness looks like to me? Perhaps all of your phenomenal
color experiences are precisely reversed with respect to mine. We have each
learned to call‘red’the color of stop signs and‘green’the color of growing
grass. But these naming conventions are achieved not by comparing our phe-
nomenal experiences of color, but by coordinating our color names to objects in
the‘external’world. What evidence can we have that each of our various private
conscious experiences are similar (or not)? It seems reasonable to assume that
my experience of red is similar to yours, but the inverted spectrum problem
seems to show that I can have no reason for this belief. - Mary the color-restricted neurologist. Mary is a brilliant (albeit imaginary)
scientist who for some science-fictional reason was forced to learn all of the
facts about color vision, but did so after living her entire life in a
black-and-white room using a black-and-white television screen and
non-colored books for her education. By hypothesis, she knows all that is
objectively knowable about the physics of color perception, even though she has
only seen shades of black and white. One day the room is opened, and Mary, for
thefirst time, sees the world in full color. Here is the question: Does Mary’s new
experience of color give her any new knowledge about color perception? She
already knows everything science has to offer about how color is perceived,
even though she only perceived black and white. Dualists claim that the story
about Mary shows that physicalists must be wrong: color perception is phe-
nomenal, and Mary’s scientific knowledge can never capture her phenomenal
experience. Physicalists claim that the whole story about Mary is bogus because
it begs important questions about the neurological basis of color vision. For
example, it assumes without argument that Mary developed the ability to per-
ceive color stimuli other than black and white without having been exposed to
them during her early development. Is this neurologically possible? We do not
know. Therefore, the dualist case is unproven. The debate was extended in an
anthology entitledThere’s Something about Mary(Ludlow et al. 2004 ). - Zombies (unfortunately so named; these are not‘the undead’but mere philo-
sophical thought tools). These are imaginary entities who are functionally
identical to ordinary humans with ordinary brains—they act like us and talk like
us—but have absolutely no phenomenal experiences. Zombies, by hypothesis,
share all physical characteristics with other human beings. They evensay that
they have phenomenal experiences. But they do not. The inverted spectrum
puzzle illustrated the impossibility of observing another person’s phenomenal
304 R. Amundson