What Sorts of Things have Consciousness?
One of the most daunting aspects of the problems of consciousness is that, apparently of necessity, I have only a single data point to work with: I know that I am conscious (in our sense of the word), and I know what my conscious experience is like, but that's all. While you can tell me that you are also conscious, and you can try to communicate to me what it is like to be you, I can never have any direct experience of anyone else's consciousness, and I know of no instruments or experiments that I can use to study, or even confirm the actuality of, any consciousness but my own.
It is, that is to say, difficult to conceive of any proof that solipsism is false. But it is equally hard to imagine a proof that it is true! So we will consider, without choosing among, a number of possible answers to the question of which objects or systems in the universe have subjective consciousness.
Solipsism: (note on the term) I am conscious, and no one (and nothing) else is. This is a rather radical thesis, but perhaps not as radical as it appears at first glance. It has little or no impact on physics, for instance, or on much of anything else except perhaps morality. If I believe that only I have inner consciousness, and my morality is based on respecting the rights only of beings with inner consciousness, I may not feel morally beholden to anyone but myself; on the other hand, those non-conscious citizens and police officers out there will still react in relatively predictable ways if I attempt to exploit this lack of moral obligation.
Solipsism has some hard problems to solve. How did I end up conscious, when no one and nothing else did? What is special about me, that I should be unique in the universe? These can be treated as challenges, though, rather than objections.
Of course, if solipsism is true, it is true only for me; anyone else who believed it of themselves (to the extent that nonconscious persons can have beliefs) would be mistaken. If solipsism were true for me, and some other person were to come to believe that I am the only conscious being in the universe, that belief would be true! (What's the word for a person who believes that someone else is the only conscious being in the universe?)
Solipsism has some other consequences: if no human is conscious but me, for instance, it must be possible to do all the things that (those other) humans do, without being conscious. Consciousness must not be a necessity (and probably not even a material advantage) for survival in the evolutionary niche that humanity occupies. In this respect, solipsism is similar to any theory that holds that consciousness does not significantly affect the physical world (see How does consciousness affect the physical world?). Of course, it is possible that my consciousness does affect the physical world, even if only I am conscious; in that case, my body is a single consciously-piloted vessel in a sea of automata.
Panpsychism: Essentially everything in the universe is conscious. There are many forms of this answer. Teilhard de Chardin and Chalmers, is it?, for instance, hold that every bit of matter has some "mental" or "nonphysical" facts that are true about it, but not necessarily full consciousness. Others hold that there is in fact "something that it is like" to be any physical object, from rocks through humans to suns and galaxies.
It's important to remember, though, that nature (physics, if you will) does not really divide the universe up into distinct "things". If there's something that it's like to be a grain of sand, is there also something that it's like to be a pile of sand? How about the set of all of the grains in the pile that are taller than they are wide? Is there something that it is like to be each atom in my body? To be my pancreas? My left hemisphere?
We know of no really systematic and convincing way to divide the universe into distinct and non-overlapping "things", such that each thing will be associated with exactly (or at most) one consciousness. That is, if every "thing" in the universe has some measure of consciousness, it seems hard to avoid the conclusion that so does every set of things, every system, every subset of the universe that it's possible to describe. This means a very large number of consciousnesses! This is not a fatal objection to the theory (Occam's Razor requires us to avoid multiplying entities only if we have some other choice), but it's something to keep in mind.
Note that in the one case where we have something that might constitute data, the findings support this answer: in "split-brain" patients where the two hemispheres of the brain have been surgically disconnected, experiments suggest that there are (at least) two distinct consciousnesses present, and that each one considers itself in charge of the body. This evidence is by no means conclusive, of course.
Any sufficiently complex system is conscious: Only systems at and above some level of complexity (and perhaps other qualities, such as integrity or coherence) have consciousness. This removes the notion (problematic for some) that there is something that it is like to be a rock, or a hydrogen molecule. But without further work it does not avoid the "really amazing numbers of consciousnesses" result above, or the somewhat non-intuitive "there's something that it's like to be all of me except for my left foot", since that system (me minus left foot) is just about as complex as all of me. Again, these results are not necessarily fatal to the theory, but they are themselves problems to be solved.
Only particular systems are conscious: There is in fact some way to pick out individual systems in the universe, and only some of those have consciousness. The most common version of this answer, of course, is that only humans (and, perhaps, other primates, other mammals, fish, hypothetical aliens and artificial intelligences) have inner experience, subjective consciousness. The set of systems endowed with consciousness can be the complex ones, or the living ones, or the sufficiently-evolved ones, or any of a host of other criteria.
This family of views encounters at full-force the questions about how the universe identifies a particular set of matter as a separate and distinct "system" to attach consciousnesses to; again, these questions may be treated as challenges rather than objections.
(Some religious answers also fall into this category. The Deity arranges for a soul, which is the seat of consciousness, to be attached to every newly-conceived embryo or equivalent, and we needn't expect physics to tell us any more about it. We probably won't have much more to say about this sort of answer, since those who hold it generally do not claim that it is accessible to logical analysis or proof. If anyone knows of an argument for this answer that is susceptible to rational examination, drop us a line.)
In general, any answer to this problem must deal with sub-problems about how the universe does (or does not) recognize boundaries between systems, and whether or not the same bit of matter can participate in the physical housings of two different consciousnesses at once. The answers to these questions will relate strongly to the answers to questions about the interaction between consciousness and the physical world (which we consider here and here).
We eagerly solicit help in this endeavor; suggestions, corrections, ideas, and references may be sent via email to email@example.com.
David Chess accepts all the blame, but Steve White gets some of the credit. If you're lost, see the site map. This page last updated January 20th, 2000.