Idealism Not all philosophical positions on the mind-body problem are dual-
istic. The opposing view ismonism: the idea that there is really just one sort
of stuff after all. Not surprisingly, there are two sorts of monist positions—
idealismandmaterialism—one for each kind of stuff there might be. A monist
who believes there to be no physical world, but only mental events, is called an
idealist (from the ‘‘ideas’’ that populate the mental world). This has not been a
very popular position in the history of philosophy, having been championed
mainly by the British philosopher Bishop Berkeley.
The most significant problem for idealism is how to explain the commonality
of different people’s perceptions of the same physical events. If a fire engine
races down the street with siren blaring and red lights flashing, everyone looks
toward it, and they all see and hear pretty much the same physical events, al-
beit from different vantage points. How is this possible if there is no physical
world that is responsible for their simultaneous perceptions of the sound and
sight of the fire engine? One would have to propose some way in which the
minds of the various witnesses happen to be hallucinating exactly correspond-
ing events at exactly corresponding times. Berkeley’s answer was that God was
responsible for this grand coordination, but such claims have held little sway in
modern scientific circles. Without a cogent scientific explanation of the com-
monality of shared experiences of the physical world, idealism has largely be-
come an historical curiosity with no significant modern following.
Materialism The vast majority of monists believe that only physical entities
exist. They are called materialists. In contrast to idealism, materialism is a very
common view among modern philosophers and scientists. There are actually
two distinct forms of materialism, which depend on what their adherents
believe the ultimate status of mental entities will be once their true physical
nature is discovered. One form, calledreductive materialism,positsthatmental
events will ultimately be reduced to material events in much the same way that
other successful reductions have occurred in science (e.g., Armstrong, 1968).
This view is also calledmind-brain identity theorybecause it assumes that mental
events are actually equivalent to brain events and can be talked about more or
less interchangeably, albeit with different levels of precision.
A good scientific example of what reductive materialists believe will occur
when the mental is reduced to the physical is the reduction in physics of ther-
modynamic concepts concerning heat to statistical mechanics. The temperature
of a gas in classical thermodynamics has been shown to be equivalent to the
average kinetic energy of its molecules in statistical mechanics, thus replacing
the qualitatively distinct thermodynamic concept of heat with the more general
andbasicconceptofmolecularmotion.Theconceptofheatdidnotthendis-
appear from scientific vocabulary: it remains a valid concept within many
contexts. Rather, it was merely given a more accurate definition in terms of
molecular motion at a more microscopic level of analysis. According to reduc-
tive materialists, then, mental concepts will ultimately be redefined in terms
of brain states and events, but their equivalence will allow mental concepts
to remain valid and scientifically useful even after their brain correlates are
discovered. For example, it will still be valid to say, ‘‘John is hungry,’’ rather
than, ‘‘Such-and-such pattern of neural firing is occurring in John’s lateral
hypothalamus.’’
6 Stephen E. Palmer