PHIL 255: Philosophy of Mind, Week 8

8a, Chalmers on Consciousness

Consciousness and the philosophy of mind

The nature of consciousness is a crucial question to many problems in the philosophy of mind. For example:

Many of these questions will recur as we discuss consciousness for the rest of the class.

David Chalmers

Chalmers is Professor of Philosophy at the University of Arizona. His 1996 book, The Conscious Mind, attracted much attention for its aggressive arguments that consciousness cannot be reductively explained in physical terms.

Easy and hard problems

Easy problems

Explain the following phenomena:

The hard problem

Why do we have conscious experience? Why is there something it is like to be conscious?

The explanatory gap

There seems to be an explanatory gap between psychological functions and experience.

E.g. Crick & Koch theorize that neural oscillations correlate with experience, but do not even begin to explain why they give rise to experience.

What extra ingredients might help to explain consciousness?

All of these still leave an explanatory gap.


Reductive explanation

Explain something by showing that it results from some underlying physical mechanism.

Examples: explain behavior of gases in terms of motions of molecules; explain inheritance of traits in terms of genes and replication of DNA.

This has been a very successful technique in modern science.

Nonreductive explanation

Chalmers claims that consciousness will not be explained reductively, but will require basic properties that go beyond those invoked by physics.

He calls his position naturalistic dualism, as opposed to spiritual dualism.


Reductionism is the hypothesis that complex systems can always be explained in terms of their parts.

Societies <- people <- organs <- cells <- molecules <- atoms < sub-atomic particles <- quarks

Reductionism implies materialism, but failure of reductive explanation does not refute materialism: reduction may fail because of complexity of the system, not because the system isn't composed of its parts.

Chalmers' theory of consciousness

Structural coherence

The structure of consciousness and the structure of awareness are coherent, i.e. there is a direct correspondence between them.

But awareness is not experience, and there is more to explaining experience than explaining awareness.

Still, "the processes that explain awareness will at the same time be part of the basis of conciousness." (p. 24)

Organizational invariance

Any two systems with the same fine-grained functional organization will have qualitatively identical experiences.

Thought experiment: if you think that functionally equivalent neural and silicon systems have different consciousness, then start replacing neurons by silicon chips. At some point there would have to be switch in experience, but the system would not notice.

Double aspect theory of information

There is a direct isomorphism between certain physically embodied information spaces and certain phenomenal (experiential) information spaces.

8b, Dennett and Churchland vs. Chalmers

Why does Chalmers think that the hard problem is not scientifically solvable?

1. Science has not yet explained consciousness.

2. He can't imagine what the explanation of consciousness would look like.

3. He thinks consciousness is fundamental, like space, time, and energy, so that it cannot be derived from anything else.

4. Thought experiments show that consciousness cannot be scientifically explained.

Dennett's reply to Chalmers

The "hard problem" formulation is misleading. Compare the problem of explaining life. In the 19th century, many people thought it required a special substance, vital force, but now we know that life is an emergent property of complex chemical systems. Similarly, heat and light have come to be understood in physical terms.

The problem of consciousness will be solved by answering the "easy" questions about the functions of consciousness. Explaining qualia is a non-issue.

Churchland's reply to Chalmers

Consciousness is a difficult problem, but no different from other scientific problems. Chalmers has invented an explanatory gap.

That someone can imagine a possibility (e.g. a zombie world) says nothing about whether it is a real possibility. It is logically possible that the heat of gases does not derive from the motion of molecules, but it does.

Chalmers' view is supported by an argument from ignorance, and scientific advances will overcome our ignorance about consciousness.


Note Chalmers' reply to Dennett and Churchland, in Shear pp. 380-386.

Is consciousness like light, heat, and life (which science has come to understand) or is it strikingly different?

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