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Mary lives in a room that is purely black and white—there
are no achromatic gradients or shades of grey in the room whatsoever. While
she is in the room, Mary learns all of the “physical” facts about light and
color vision (i.e., All that neuroscience and physics have to say about light
and color vision and the relationships between different colors). For example,
while Mary is in her room, she learns that the color red is identical to light
wavelengths of 625nm to 700nm, the color blue is identical to light wavelengths
of 450nm to 485nm, the color green is identical to light wavelengths of 500nm to
565nm, and the color yellow is identical to light wavelengths of 565nm to 590nm.
Mary also has memorized the sequence of colors in order of shortest-to-longest
wavelengths.
One day Mary leaves the room (which, as we must keep in
mind, was purely black and white without any kind of shading or achromatic
gradient mediating between the black and white). Mary is then escorted to a
table where a couple of fellow scientists are waiting for her. On the surface
of the table lies an assortment of colored tiles (which are not in any
particular order or arrangement; they are simply “scattered” and “mixed up”).
There is one red tile, one blue tile, one green tile, and one yellow tile. Mary
(who had learned all of the “physical” facts about light and color vision;
indeed, she has even memorized the light wavelengths of red, blue, green, and yellow) is told—on the spot—the following: “Mary, you are in the presence
of four colored tiles. Arrange the colored tiles in the order of
shortest-to-longest wavelengths.”
It’s clear that Mary would be stumped.
Another scientist interrupts the silence and says, “Mary,
with your left hand, pick up the red tile, or the tile whose color is identical
to wavelengths of 625nm to 700nm; and, with your right hand, pick up the green
tile, or the tile whose color is identical to the wavelengths of 500nm to 565nm.”
It is pretty clear that (i) Mary would not know which four
tiles to pick up with her left hand and (ii) Mary would not know which
of the four tiles to pick up with her right hand.
Despite her exhaustive knowledge of all the “physical” facts about light and color vision, Mary would not know which of the four colored
tiles presented to her was the red tile and which of the four tiles was the
green tile.
After a few moments without any answer from Mary, one of the
scientists places the red tile in Mary’s left hand and says, “This is red.” The
other scientist then places the green tile in Mary’s right hand and says, “This
is green.” Upon hearing these statements, Mary learns new facts about light and
color vision; namely that there are drastic qualitative differences and
similarities between red and green—e.g., they have different sensory
characteristics; one is “softer” than the other; one is “warmer” than the
other; one is more “vibrant” than the other; and one is less “harsh” and more
“mellow” than the other. One of the scientists then picks up the yellow tile
and tells Mary, “This is yellow.” Upon hearing this statement, Mary, again,
learns another new fact about light and color vision; namely
the fact that yellow is more “vibrant” than green—which is “mellower”—and
that the qualitative character of yellow is lighter and less “imposing”
than red.
Now, suppose, on the other hand, the situation was altered.
Suppose that immediately after Mary left her room, one of the scientists placed
the red tile in Mary’s left hand and said, “This is green;” and the other
scientist placed the green tile in Mary’s right hand and said “This is red.”
Clearly, if Mary learned all the “physical” facts about light and color vision,
she would immediately respond by saying “You both are wrong. The green tile is in
my right hand, and the red tile is in my left.” However, it’s obvious that upon
leaving her room, Mary would have no idea that she was being told falsehoods
about the colors of the tiles—indeed (after being told that the red tile in her
left and was green, and the green tile in her right hand was red) she would
think that the red tile was green and
the green tile was red. However, red and green have
different wavelengths—and Mary would have known this upon her release.
If Mary knew all there is to know about light
and color vision, then Mary should have been able to identify the colors of the
tiles and arrange them in sequence of shortest-to-longest wavelengths upon her
release, without hesitation. And yet, she couldn’t. Thus, since Mary knew all
of the “physical” facts about light and color vision before leaving her room (i.e.,
All that neuroscience and physics have to say about light and color vision
and the relationships between different colors), it follows that not all facts
are “physical” facts.