Think: A Compelling Introduction to Philosophy by Simon Blackburn Page A

whole
classroom may see some neurones firing, but only the one person feels the pain. Descartes actually located the place where the magical event takes place. For quite sensible neurophysiological reasons
he thought that the pineal gland, a structure lying centrally within
the brain, must be the place where messages were conducted from
the realm of physics to the realm of the mental.

    For Descartes it is not only that mental events are distinct from
physical events. They also belong to a distinct kind of substanceimmaterial substance-a kind of ghost-stuff or ectoplasm. Strictly
speaking if I say, `I thought of the Queen and I saluted,' there is a
kind of ambiguity: the`l'that is the subject of the thought is not the
`I, the body, that salutes. Thoughts and experiences are modifications in one kind of stuff; movement and position belongs to the
other. This part of Descartes's doctrine marks him as a 'substance
dualist: It is not just that there are two kinds of properties (mental
properties and physical properties) and that persons can have
both. It is that there are two kinds of bearers of properties as well.
Of course this is theologically convenient: it opens the way to the
immortality of the soul, since there is no reason for soul-stuff to
have the same life span as anything like a physical body. But substance dualism is not compulsory. One could hold that mental and
physical properties are very different but that the one organized
body has them both-after all, mass and velocity are two very different kinds of property, but projectiles have them both. People
who hold that there are two kinds of property (mental and physical) but that they can belong to the one kind of stuff (whatever
large animals are made of) are called property dualists.
    Descartes leads us to the view neatly summed up by Gilbert Ryle
(1900-76) as holding that the human being is a'ghost in a machine' Events in the machine, the physical body, are like other events in
the physical world. They consist in the interactions of familiar
kinds of stuff: molecules and atoms, electrical fields and forces.
Events in the ghostly part, the mind, are altogether different. Perhaps they are events in some kind of ghost-stuff-ectoplasm, or
the non-physical stuff that spirits and angels are made of. Spirits
and angels do without the physical embodiment altogether, in the
popular mind. But in the normal human being there is a close correlation between events of the one kind and those of the other:
sticking a pin in someone makes physical changes, but it also
causes a mental event of feeling pain. And vice versa: the mental
event of remembering a blunder may cause physical events such as
groaning and blushing. So events in the one realm may affect those
in the other. But in principle the two realms are entirely distinct.

    ZOMBIES AND MUTANTS
    Of course, this view is not peculiar to Descartes. It is the view presupposed by many of the world's great religions: it is part of any
doctrine holding that we can survive bodily death, or that our soul
can go one way while our body goes another. Yet it is a view that
faces enormous, and arguably insurmountable, problems.
    The first family of problems is epistemological. I just said that in
the normal human being there is a close correlation between
events of the one kind and those of the other. But how are we entitled to believe that? Here is one way things might be:

    The Zombie Possibility. Zombies look like you and me,
and behave like you and me. Their physical natures are indistinguishable. If you opened a Zombie brain, you would
find that it functions exactly the same way as your brain or
mine. If you prick a Zombie, he or she will go `ouch', just like
you or me. But Zombies are not conscious. There is no
ghost within.
    Because Zombies look and behave just like you and me,
there is no way of telling which of us are Zombies and
which are conscious in the way that you and I are. Or at