The hard problem is often illustrated by
appealing to the logical possibility of inverted
visible spectra. If there is no logical
contradiction in supposing that one's colour
vision could be inverted, it follows that
mechanistic explanations of visual processing
do not determine facts about what it is like to
see colours.
A swarm of birds showing high
order structure emerging from
simpler physical constituents
physical constituents. For example, water is nothing
more than H2O molecules, and understanding everything
about H2O molecules is to understand everything there is
to know about water. But consciousness is not like this.
Knowing everything there is to know about the brain, or
any physical system, is not to know everything there is to
know about consciousness. Consciousness, then, must
not be purely physical.[27]
Chalmers's idea contradicts physicalism, sometimes
labelled materialism. This is the view that everything that
exists is a physical or material thing, so everything can
be reduced to microphysical things. For example, the
rings of Saturn are a physical thing because they are
nothing more than a complex arrangement of a large
number of subatomic particles interacting in a certain way.
According to physicalism, everything, including consciousness,
can be explained by appeal to its microphysical constituents.
Chalmers's hard problem presents a counterexample to this view
and to other phenomena like swarms of birds, since it suggests that
consciousness, like swarms of birds, cannot be reductively
explained by appealing to their physical constituents. Thus, if the
hard problem is a real problem then physicalism must be false, and
if physicalism is true then the hard problem must not be a real
problem.
Though Chalmers rejects physicalism, he is still a naturalist.[27]
The hard problem of consciousness has scholarly antecedents considerably earlier than Chalmers.
Chalmers himself notes that "a number of thinkers in the recent and distant past" have "recognised the
particular difficulties of explaining consciousness."[33] He states that all his original 1996 paper
contributed to the discussion was "a catchy name, a minor reformulation of philosophically familiar
points".[33]
Among others, thinkers who have made arguments similar to Chalmers' formulation of the hard problem
include Isaac Newton,[34] John Locke,[35] Gottfried Wilhelm Leibniz,[36][34] John Stuart Mill,[37] and
Thomas Henry Huxley.[38][34] Likewise, Asian philosophers like Dharmakirti and Guifeng Zongmi
discussed the problem of how consciousness arises from unconscious matter.[34][39][40][41]
Implications for physicalism
Historical precedents
Related concepts
The mind–body problem