Philosophical Zombies and the Physical Basis of Consciousness

Given that the Walking Dead is back with a new season and World War Z has just ripped through the public conscious I thought that the philosophical implications of zombies would be a worthwhile subject for a post. I would not be the first person to have thought about what the notion of a zombie means for consciousness, and in fact the zombie has a well entrenched place in a series of arguments about the nature of the relationship between mind and matter.

Before we get under way, it is worth noting that to philosophers versed in the age old tradition of the Thought Experiment, a zombie is not a flesh eating monster that shambles around slowly decomposing and smelling disgusting. A philosophical zombie is merely a person without consciousness. I can hear you all respond "Que?" followed by quizzical silence. The idea is to ask if we can conceive of a person who acts and behaves like we do without the mental qualia of consciousness, that is the internal experience of seeing red, smelling roses and the pain of being pricked by a thorn.

The way this is taken to impact on our understanding of mind and brain relies on a second philosophical trick: the notion of a conceivability argument. This is the idea that if we can conceive of something then it is in some sense at least possible. Usually this is taken as metaphysical possibility, i.e. that it may not be possible in this universe, but in some other universe. If you think this is a pretty slippery way to argue, then you are in good company. Nevertheless, it persists as a philosophical tool, and for the sake of this post I am going to grant it temporary validity.

Ok. So.

The argument goes as follows: physicalist explanations of consciousness require that there be some configuration of matter that corresponds to conscious states. If we can conceive of a zombie, then it is metaphysically possible that a being could exist that can act as we do, yet is not conscious. As that means that the zombie must have the configuration of brain matter that allows the specific conscious-like behavior, therefore that configuration of brain matter cannot be the source of consciousness.

However, even allowing the conceivability argument, this is still an invalid argument. The reason is that just because for homo sapiens we observe certain configurations of brain matter that give rise to the set of behaviors and conscious states, it does not preclude the existence of other arrangements that have the former but not the latter. It is equivalent to observing a bunch of four legged tables and concluding that table-ness and four-legged-ness are a necessary combination. In reality other arrangements of legs can also make tables, and four legs does not always a table make.

Strengthening this objection is the fact that we know that the micro-structure of our brains are different between individuals. In fact, this is the source of our individuality. While the macro-structural features of our brains are shared (thalamus, hypothalamus, corpus callosum, regions of the cerebral cortex and their inter-connectedness), the fine grained structures that control our thoughts and actions are (virtually) unique. This means that in reality there is no a single configuration of brain matter that gives rise to a given set of behaviors and their corresponding conscious states, but rather a family of configurations.

There is nothing preventing this family of configurations being broader than we know them to be, and a certain (as of yet unobserved) set of them having the property of giving rise to behaviors without conscious states. This might seem far-fetched, but as I can conceive of it, it must be meta-physically possible.