In the 1990s Australian philosopher David Chalmers framed the challenge of distinguishing between the “easy” problems and the “hard” problem of consciousness. Easy problems involve explaining behavior, such as the ability to discriminate, categorize and react to surprises. Still incredibly challenging, they’re “easy” in the sense that they fit into standard scientific investigation: we postulate a mechanism to explain how the system—the brain—does what it does.
The hard problem comes after we’ve explained all of these functions of the brain and are still left with a puzzle: Why is the carrying out of these functions accompanied by experience? Why doesn’t all this mechanistic functioning go on “in the dark”? In my own work, I have argued that the hard problem is rooted in the way the “father of modern science,” Galileo, designed physical science to exclude consciousness.
Chalmers made the conundrum vivid by promoting the idea of a “philosophical zombie,” a complicated mechanism set up to behave exactly like a human being, with the same information processing in its brain, but with no consciousness. You stick a knife in such a zombie, and it screams and runs away. But it doesn’t actually feel pain. When a philosophical zombie crosses the street, it carefully checks that there is no traffic, but it doesn’t actually have any visual or auditory experience of the street.
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Given that we’re not zombies, there must be something more going on in us to explain our consciousness.
Nobody thinks zombies are real, but they offer a vivid way of working out where you stand on the hard problem. Those on Team Chalmers believe that if all there was to a human being were the mechanistic processes of physical science, we’d all be zombies. Given that we’re not zombies, there must be something more going on in us to explain our consciousness. Solving the hard problem is then a matter of working out the extra ingredient. One increasingly popular option is to posit very rudimentary forms of consciousness at the level of fundamental particles or fields.
For people on the opposing team, such as the late, great philosopher Daniel Dennett, this division between feeling and behavior makes no sense. The only task for a science of consciousness is explaining behavior—not just the external behavior of the organism but also that of its inner parts. This debate has rattled on for decades.
More recently, however, there has been a new and interesting development in these philosophical debates. Growing numbers of philosophers suspect that the division between “feelings” and “behavior,” inspired by zombies and by the distinction between hard and easy problems, poses an even deeper challenge than Chalmers foresaw. This outcome may tempt us to think that Dennett was right after all and that the whole “hard problem” setup is a chimera.
Or it may lead us to conclude that the mind is more mysterious than has thus far been appreciated.
The problem is that once we commit to the possibility of zombies, we can’t just stop at vanilla ones. If it makes sense to separate out consciousness and behavioral functioning, then it also makes sense to mix and match them in weird ways. We could imagine, for example, color inverts: beings who are physically just like us but experience color differently—when they look at bananas, they have the same experience that we have when we look at tomatoes, and vice versa. Many teenagers first get into thinking about philosophy through musing on such possibilities (too often, admittedly, in dorm rooms).
Here’s a stranger kind of mix-and-match zombie: pain-pleasure inverts who behave just like us but feel pleasure when we feel pain, and vice versa. When you stick a knife in a pain-pleasure invert, they feel great pleasure, but this pleasure causes them to scream and run away. When pain-pleasure inverts eat and drink, they feel terrible pain, but this pain causes them to keep eating and drinking.
Something seems wrong here: Pain-pleasure inverts seem nonsensical. But if we accept Chalmers’s conceptual distinction between behavioral functioning and subjective experience, then pain-pleasure inverts ought to be just as conceivable as regular zombies. The only way to reject the coherence of pain-pleasure inverts is to reject the initial division between the easy problems of behavior and the hard problem of conscious experience.
I argue a lot about philosophy on social media, and I’ve found that many people think evolution would explain why we’re not pain-pleasure inverts. But if you consider it carefully, that doesn’t make sense. Natural selection is going to favor making me feel pain when my body is damaged only if that feeling is going to lead me to avoid such damage. If we lived in the bizarre universe of pain-pleasure inverts, where pleasure generally leads to avoidance behavior and pain to attraction behavior, then we would have evolved to feel pleasure when our body is damaged and pain when we eat and drink. Pain-pleasure inverts that eat and reproduce would pass on their genes just as well as we do. In other words, evolutionary explanations of our consciousness presuppose that we’re not pain-pleasure inverts, just as they presuppose the existence of self-replicating life. In either case, evolution cannot explain what it already assumes.
Why does this matter? If consciousness and behavior could come apart in other possible universes, then we need to explain not only why they come together in the human brain but also why they come together in a rational and coherent way. This question has become known as the mystery of psychophysical harmony. The pain-pleasure examples are just the most vivid case. More generally, any historical or sociological explanation (for example, of why people voted a certain way in an election) assumes that human beings respond in a more or less rational way to their conscious beliefs and desires. But if we are physical objects in a meaningless, purposeless universe, why should our behavior and our consciousness work together in a coherent and rational way? Why aren’t we some kind of weird mix-and-match zombie?
Some philosophers have argued that psychophysical harmony points to God. I think that’s a bit of an overreaction, but I have argued that dealing with psychophysical harmony takes us in radical directions, uprooting our most fundamental assumptions about reality. Since the scientific revolution, we have conceived of laws of nature as working from past to present, meaning what happens in the present is dependent on what happened a moment earlier. I believe we can make rigorous scientific sense of teleological laws that work from future to present, ensuring that what happens in the present is dependent on the need to get closer to some future goal, such as the goal of harmonious alignment of consciousness and behavior.
For some, this is a bridge too far and further proof that Dennett was right all along. For my own part, I feel that once you’ve crossed over to this understanding of consciousness, you cannot return. As William Shakespeare wrote in Macbeth:
I am in blood
Stepped in so far, that, should I wade no more,
Returning were as tedious as go o’er.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.
