patterns. A clock, a hurricane, and the easy problems, are all the sum of their parts (as are most
things).[27]
The easy problems relevant to consciousness concern mechanistic analysis of the neural processes that
accompany behaviour. Examples of these include how sensory systems work, how sensory data is
processed in the brain, how that data influences behaviour or verbal reports, the neural basis of thought
and emotion, and so on. They are problems that can be analyzed through "structures and functions".[27]
The hard problem, in contrast, is the problem of why and how those processes are accompanied by
experience.[1] It may further include the question of why these processes are accompanied by this or that
particular experience, rather than some other kind of experience. In other words, the hard problem is the
problem of explaining why certain mechanisms are accompanied by conscious experience.[27] For
example, why should neural processing in the brain lead to the felt sensations of, say, feelings of hunger?
And why should those neural firings lead to feelings of hunger rather than some other feeling (such as,
for example, feelings of thirst)?
Chalmers argues that it is conceivable that the relevant behaviours associated with hunger, or any other
feeling, could occur even in the absence of that feeling. This suggests that experience is irreducible to
physical systems such as the brain. This is the topic of the next section.
Chalmers believes that the hard problem is irreducible to the easy problems: solving the easy problems
will not lead to a solution to the hard problems. This is because the easy problems pertain to the causal
structure of the world while the hard problem pertains to consciousness, and facts about consciousness
include facts that go beyond mere causal or structural description.[32]
For example, suppose someone were to stub their foot and yelp. In this scenario, the easy problems are
mechanistic explanations that involve the activity of the nervous system and brain and its relation to the
environment (such as the propagation of nerve signals from the toe to the brain, the processing of that
information and how it leads to yelping, and so on). The hard problem is the question of why these
mechanisms are accompanied by the feeling of pain, or why these feelings of pain feel the particular way
that they do. Chalmers argues that facts about the neural mechanisms of pain, and pain behaviours, do not
lead to facts about conscious experience. Facts about conscious experience are, instead, further facts, not
derivable from facts about the brain.[27][32]
An explanation for all of the relevant physical facts about neural processing would leave unexplained
facts about what it is like to feel pain. This is in part because functions and physical structures of any sort
could conceivably exist in the absence of experience. Alternatively, they could exist alongside a different
set of experiences. For example, it is logically possible for a perfect replica of Chalmers to have no
experience at all, or for it to have a different set of experiences (such as an inverted visible spectrum, so
that the blue-yellow red-green axes of its visual field are flipped).[32]
The same cannot be said about clocks, hurricanes, or other physical things. In those cases, a structural or
functional description is a complete description. A perfect replica of a clock is a clock, a perfect replica of
a hurricane is a hurricane, and so on. The difference is that physical things are nothing more than their
Hard problem
How the easy and hard problems are related