Imagine that one day that basic components of the world were instantaneously replaced by other things, in a one-to-one correspondence, which had the same patterns of interactions (the same functional properties) as the things they replaced. Would we notice the change? I don’t think we could. Since all our instruments, both scientific devices and our natural ability to perceive the world, are working the same way as they did before they would report the same information to us. This is of course an extension of my previous claim about properties, namely that the basic properties are best identified with a specific kind of causal disposition, which is another way of saying that the basic properties are functional properties.
Now if we accept that the world would remain exactly they way it currently is, at least apparently, as long as all the functional properties are preserved, then we must accept that every property ultimately reduces to functional ones. I think that most would agree to this in principle for many cases. But there are those who may insist that certain properties depend on the nature of the substance. For example, some may argue that the property of being metal depends on the object really being composed of certain kinds of atoms, and not just having certain properties. But what is it to be a certain kind of atom? Well since everything is effectively unchanged under replacement, given that functional properties are held constant, we can conclude that being a certain kind of atom is effectively identical to having a certain complex causal disposition. Thus to identify being a metal with being made up of certain kinds of atoms is really to identify being a metal with being made up of components with certain kinds of causal dispositions. But that is a functional property (it depends on the functional relations between parts of the object and the functional relations of those parts to the external world). And hence being metal is really a functional property, even though it doesn’t seem like one.
Since everything reduces to functional properties we can conclude that consciousness too reduces to functional properties. Obviously his contradicts, to some extent, the claims of those who say that consciousness is a uniquely biological property. But, they might claim that the functional properties found in biological systems are unlike those found in systems like computers. Biology, they might point out, works in parallel, while computers are serial. To determine if this, or a response like it, can succeed in defending the position that consciousness is a purely biological affair we need to understand how a system is determined to have various functional properties.
Specifically I would like to point out that a single system can be validly described as having numerous different sets of functional properties. Consider a system with three basic parts, A, B, and C. And for simplicity let us say that A only acts upon B, B upon C, and C upon A. Obviously one way to describe the functional properties of this system is in terms of A, B, and C. Let us call this the [A-B-C] description of the system. But we could equally validly describe the functional properties of the system in terms of the interaction between A and the combination of B and C. We can call this the [A-BC] description. Obviously the [A-BC] description in some sense leaves out some of the information that the [A-B-C] description includes, but of course this doesn’t make it an invalid description of the system. Now we can consider a system with two parts Y and Z. And this system might have a [Y-Z] description. Now it is perfectly possible for [A-BC] and [Y-Z] to be the same description; both descriptions include two parts, and there is nothing preventing those two parts from having the same interactions. If this is indeed the case then the A-B-C system and the Y-Z system would have some of the same functional properties, and if the Y-Z system has some property by virtue of its functional properties then the A-B-C system has it too, since there is a valid description of that system in which it has all the functional properties of the Y-Z system.
Obviously there are a vast number of functional descriptions of the human brain. Of the almost unaccountably many functional descriptions that fit the brain there are four that we tend to talk about most often. One is the description that captures every interaction of every atom, one that captures the interactions of the neurons, one that captures the interactions of the neuron groups, and one that captures only the interactions of the brain with the external world. We can call these descriptions [atomic], [neuronal], [cluster], and [whole] respectively. Now if the biological brain has the property of being conscious it must be because some particular functional description can be said to apply to it. Remember, we have already established that all properties must be identical with some kind of functional properties. Let’s suppose, arbitrarily, that the important functional properties are the ones captures by the [neuronal] description. (Note: identifying consciousness with the properties of [whole] is behaviorism.)
Obviously the functional description of a computing machine that captures every fact about it will not be identical with any functional description of a biological brain. But, like the brain, we can describe the functional properties of the computer at higher and higher levels of abstraction. At some level the relevant parts captured by the functional description of our computing machine will correspond to the interactions between various software constructs, and not directly to any of the features of the physical implementation of the machine. But the functional interactions of software constructs are completely arbitrary, we can program the machine so that the software constructs have any sort of functional properties we wish, given that we have some finite description of those properties in mind that we can program them to conform to (Church’s thesis*). Certainly we can program them to display the same properties as [neuronal], since that description is finite and well defined, since the brain is of finite size and is governed by natural law. Thus we can program our computer to have the functional properties that we had previously said that consciousness depended on. And this is true no matter which set of the functional properties of the brain that we think consciousness depends on.
Thus, if we accept that all properties are ultimately functional properties, consciousness, being some functional property of our biological brains, must ultimately be able to be found in non-biological systems of sufficient complexity as well.
* The reason (or one way of looking at the reason) we can’t program computers to do things like solve the halting problem is because when you begin to specify in detail how the machine should function in order to solve the halting problem you begin to realize that you can’t give a finite recipe for determining if an arbitrary program will halt without running it and seeing whether it does halt or not. Of course humans can’t solve the halting problem either, so it is not like this is a serious limitation on the power of computers, any more than it is a serious limitation on our thinking power. And yes, the functional properties of a process that acts in parallel can be fully captured by a computing machine that works serially.