The situation is perhaps best understood by analogy to the emergent property
of being alive. Ordinary matter manifests this property only when it is orga-
nized in such a way that it is able to replicate itself and carry on the required
biological processes. The difference, of course, is that being alive is a property
that we can now explain in terms of purely physical processes. Property dual-
ists believe that this will never be the case for mental properties.
Even if one accepts a dualistic position that the mental and physical are
somehow qualitatively distinct, there are several different relations they might
have to one another. These differences form the basis for several varieties of
dualism. One critical issue is the direction of causation: Does it run from mind
to brain, from brain to mind, or both? Descartes’s position was that both sorts
of causation are in effect: events in the brain can affect mental events, and
mental events can also affect events in the brain. This position is often called
interactionismbecause it claims that the mental and physical worlds can interact
causally with each other in both directions. It seems sensible enough at an in-
tuitive level. No self-respecting dualist doubts the overwhelming evidence that
physical events in the brain cause the mental events of conscious experience.
The pain that you feel in your toe, for example, is actually caused by the firing
of neurons in your brain. Convincing evidence of this is provided by so-called
phantom limb pain, in which amputees feel pain—sometimes excruciating pain—
in their missing limbs (Chronholm, 1951; Ramachandran, 1996).
In the other direction, the evidence that mental events can cause physical
ones is decidedly more impressionistic but intuitively satisfying to most inter-
actionists. They point to the fact that certain mental events, such as my having
the intention of raising my arm, appear to cause corresponding physical
events, such as the raising of my arm—provided I am not paralyzed and my
arm is not restrained in any way. The nature of this causation is scientifically
problematic, however, because all currently known forms of causation concern
physical events causing other physical events. Even so, other forms of causation
that have not yet been identified may nevertheless exist.
Not all dualists are interactionists, however. An important alternative ver-
sion of dualism, calledepiphenomenalism,recognizesmentalentitiesasbeingdif-
ferent in kind from physical ones yet denies that mental states play any causal
role in the unfolding of physical events. An epiphenomenalist would argue that
mental states, such as perceptions, intentions, beliefs, hopes, and desires, are
merely ineffectual side effects of the underlying causal neural events that take
place in our brains. To get a clearer idea of what this might mean, consider the
following analogy: Imagine that neurons glow slightly as they fire in a brain
and that this glowing is somehow akin to conscious experiences. The pattern
of glowing in and around the brain (i.e., the conscious experience) is clearly
caused by the firing of neurons in the brain. Nobody would question that. But
the neural glow would be causally ineffectual in the sense that it would not
cause neurons to fire any differently than they would if they did not glow.
Therefore, causation runs in only one direction, from physical to mental, in an
epiphenomenalist account of the mind-body problem. Although this position
denies any causal efficacy to mental events, it is still a form of dualism because
it accepts the existence of the ‘‘glow’’ of consciousness and maintains that it is
qualitatively distinct from the neural firings themselves.
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