Like what Richard Feynman may have once said about quantum mechanics: if you think you understand consciousness, you don’t understand consciousness. Consciousness is baffling and that is primarily because it is difficult to reconcile our personal conscious experience with a physical, materialist understanding of the world.
What is consciousness? There is no single, authoritative definition, but I will define it as an internal subjective experience. If you have consciousness, there is something that it is like to be you, i.e. you have sensations, feelings, and thoughts that you experience subjectively. Thomas Nagel framed the issue in this way in his seminal article, “What is it like to be a bat?” Consciousness is an inherently private phenomenon, and there doesn’t seem to be any way for anyone else to verify your consciousness beyond any doubt. There are of course indicators that suggest you are conscious, but no one can know for sure if you are having an internal experience – no one can know exactly what it is like to be you.
Why does consciousness seem to be incompatible with a physicalist understanding of the world? This is because if you were to look inside someone’s head and analyze her brain, all you would find are neurons and the chemicals and electrical signals they use to communicate with each other. There is no central place in the brain where a person’s subjective, first person perspective exists. You would find no evidence of a mind, you would find no representation of the external world, and you would find no qualia (the phenomenal aspects of consciousness). If you could not find these things – the things that make up our subjective experience – how could you say they actually exist?
And yet, at the same time, it is impossible to deny that these things exist! They are the only things we know for sure exist. Consider the “brain in a vat” thought experiment, which states that you are actually just a brain in a vat hooked up to an elaborate computer program that tricks you into thinking you are experiencing the outside world. The entire external world could be an illusion. Or you could be experiencing a dream. The only thing you know for sure exists, and that you can’t deny, is your own consciousness.
While you can’t deny your own consciousness, it is conceivable to deny the consciousness of others. Everyone else in the world might be a philosophical zombie, or a being that looks and acts like they are conscious, but there is actually no subjective experience on the inside. I don’t think philosophical zombies are likely because I believe that consciousness is generated by the brain, and since other people have brains more or less similar to my own, they most likely have consciousness, as well.
I should mention that there are strong arguments that the brain generates consciousness. We know that specific mental states and cognitive processes are linked to specific regions of the brain. If you damage certain parts of the brain, specific aspects of consciousness and personality change. And of course, if the brain fails, consciousness goes away completely.
What about animals – do they have consciousness? It is important to know because if they have consciousness, they can suffer and experience pain. Thus, knowing if they do informs how we as humans treat them. I think it is very likely that animals with larger brains have consciousness. Apes, dogs, cats, elephants, and dolphins all exhibit behaviors that suggest consciousness. But as you move towards animals with smaller and smaller brains, they seem to be less conscious. The question then becomes, where along the spectrum does consciousness vanish completely? And it probably does at some point. I doubt anyone would argue that some insects, jellyfish, and microscopic animals have internal subjective experiences.
But this raises an interesting question – at which point in the evolutionary process did consciousness arise? When did a living organism first experience qualia? How does inanimate matter reach a point where it is able to have a subjective experience? I don’t have the answers to these questions, but I hope that science will one day find them.
I think we will learn more about consciousness as we develop more advanced robotics and artificial intelligence. At some point, it seems very likely that we will create machines that are more intelligent than humans. Will they have consciousness? Or will they be philosophical zombies? It seems likely that if we were able to replicate in robots the same cognitive processes that take place in the brain, then those robots would be conscious. If and when that happens, our confidence that they are conscious would be as strong as our confidence that other humans are conscious.
Finally, some have argued that consciousness is some kind of illusion. The world would make a lot more sense if we didn’t have consciousness and we were all philosophical zombies. But if consciousness is an illusion, it is an unshakable illusion, and it is the very essence of our lived experience.