state—a personal feel of redness for example. The zombie example claims that
we can imagine people who have no phenomenal states at all but have bodies
and brains just like everyone else. Dualists claim that because zombies are
imaginable, but very different from ordinary people, the imaginability of zom-
bies proves that ordinary people are something in addition to their physical
properties. Naturally, physicalists disagree. They claim that the mere fact that
we canimaginea zombie does not mean that they arepossiblein the sense
required to prove that phenomenal experiences require non-physical properties.
Imaginability does not prove possibility.The arguments continue with no likelihood of quick resolution. The thought
experiments are intended to show that subjective experience cannot be explained by
neurology alone or for that matter by any other purely physical process.
Philosophers of mind vary in their opinions about what they prove. Small wonder
that human biologists who venture into similar areasfind puzzles of their own.
There is some agreement among philosophers regarding phenomenal experience
or what we commonly call mental experiences. One distinctive feature is that such
experiences areepistemically privileged.We have special kinds of knowledge about
the phenomena, and such knowledge comes with an especially high degree of
certainty. I know with certainty that a certain patchlooks red, even though I may be
mistaken about what in the objective world caused me to perceive the patch.
A related point is that no one else in the world can have evidence that can rea-
sonably cause me to doubt my own honest beliefs about the phenomenal appear-
ance of the patch. A very clever neurologist might be able to infer that I am seeing a
reddish patch by watching my fMRI output, but if we disagree, the neurologist (and
not me) must be mistaken. My epistemic privilege trumps the neurologist’s
objectively based opinion, no matter how long his educational career or how short
mine. (To simplify the discussion, I will sidestep an interesting anthropological
complication, by assuming that the neurologist and I share our culture. Many
anthropologists are aware that different languages have different numbers of color
words and somewhat different ways of dividing up the color spectrum. The pos-
sibility that this shows that people from different cultures actually perceive colors
differently will be ignored for the moment.)
This excursion into deepest philosophy raises the following questions: Are the
biological and health correlates of the biomarkers discussed in this volumesub-
jectivein a sense similar to the subjectivity of phenomenal experience? Can a
philosophical distinction be drawn between (objective) biomarkers and the (sub-
jective) experiences that they mark, paralleling the distinction between my objective
brain states and my subjective phenomenal experiences? The objective–subjective
dichotomy does touch on a few of the biomarkers here discussed, but not all of
them. Some biological correlates are themselves purely objective, equally objective
as their biomarkers. Blood test results may be an example, e.g., cholesterol levels.
But the biomarkers all mark factsabout us, and some of those are facts about which
we consider ourselves to beprivileged knowers. If we are privileged knowers about
our health conditions, our privilege might challenge the legitimacy of the
14 Subjective and Objective Knowledge: Persistent Puzzles 305