So much is written on the subject (consciousness) based on so many
different definitions that we first need to make explicit what we
mean by consciousness.
Together with Gray and Velmans I choose (opt) for a pragmatic approach,
closest to daily life. Consciousness or conscious awareness refers
to the subjective experiencing of phenomenal content. It is the implicit
notice of a 'whole me' that is experiencing something. 'Implicit'
because we don't need to be (meta)conscious of the fact that it is
me experiencing something, while at the same time consciousness has
everything to do with my perspective (that of my body's, that is...)
For an overview of definitions i would recommend to read Velmans and
a special theme number of the Journal of Consciousness Studies about
Theories of consciousness can be roughly divided into dualist and
theories are based on the ideas of Plato and later Descartes, who
consider mind and matter as two different substances that interact
but cannot be reduced to eachother. For an extensive review I recommend
Velmans. Although dualist theories have become less popular in our
time, there are still scientists advocating it. These theories generally
claim dualist-interactionism, in which consciousness has causal power
on the material world and vice versa. Eccles for example assumed that
the self-conscious mind has non-material existence of its own, being
able to influence brain processes and giving a special status to free
will. According to Eccles consciousness could not have developed by
natural selection if it only were an epiphenomenon. Other examples
are the quantum theory of consciousness from Hameroff and Penrose
(see Gray for an extensive analysis) and the theories that equal consciousness
with electromagnetic field generated and fed back to brain networks
These theories have in common that they assume that "autonomously
existing experiences can have two-way interactions with the brain"
(Velmans). In order for consciousness to influence brain states there
should be a gap in neural causation chains to operate. As far as evidence
suggests, the physical world is causally closed.
Dualist-interactionism theories have many problems, like explaining
how something immaterial could influence matter without violating
the Second Law of Thermodynamics (conservation of energy).
theories of consciousness try to reduce mind and matter to a common,
underlying principle. That can be mind (idealism), matter (physicalism,
functionalism) or something else (duals-aspect theory, neutral monism,
Spinoza considered mind and body being different aspects of one underlying
reality that you can give any name (Nature, God). It corresponds with
my concept of Cruality, which refers to 'unknowable reality'. Modern
varieties are dual aspect theories of information (Velmans, Nagel,
Chalmers). Neutral monism takes the stance that what we see is neither
intrinsically mental or physical. We judge what we experience to be
that. (zie Mach, in Velmans p.32). It corresponds with my concept
of 'nested sensation'. (see my notes in Velmans)
Idealism claims that things only exist in the mind. A special version
is the Copenhagen interpretation of Quantum Mechanics (Velmans, p.
37) that assumes things coming into existence only through observation
(the act of observation makes the wave form collapse). However, perception
is bound to observation, material processes continue on their own
even when not observed (like the apple pie baking in the oven).
Physicalism is the strongest represented view in modern science. It
reduces consciousness to a state of the brain. But it leaves us with
a big gap between conscious experience and (measured) brain states.