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The Problem

What is the problem of consciousness? If there's one most pressing worry about consciousness in contemporary philosophy, it's what philosopher David Chalmers calls "the hard problem" (Chalmers 1996). It's the problem of explaining why anything physical is conscious at all. More specifically, why do certain physical brain processes result in the subjective experience of color, rather than experiences of sound or no experiences whatsoever? The problem is a version of an older philosophical conundrum, the so-called "mind-body problem," famous from the work of René Descartes. The hard problem of consciousness is where much of the fighting over the mind-body problem ends up after the rise of modern psychology, cognitive science, and neuroscience. Consciousness seems to be the remaining bit that fails to fit nicely into the modern scientific worldview. Even after we've explained all of what the brain does, down to the finest neural detail, the hard problem of consciousness appears unanswered. The hard problem, and philosophers' attempts to deal with it, is the main focus of this book.

But what is consciousness? As with many philosophical questions, even agreeing on the thing we disagree about is difficult! How we pick out consciousness in the first place can have big implications for how hard the hard problem appears. If we define consciousness as "the mysterious, unknowable core of human experience," then it's not surprising that consciousness seems inexplicable. But if we define consciousness as "whatever causes our verbal reports about how we feel," then we may be defining a real mystery out of existence at the get-go. So it would be nice if we can find a way to characterize consciousness that neither builds in unsolvable mystery, nor rules it out by stacking the explanatory deck. While there isn't a single agreed-upon definition in contemporary philosophy, unfortunately, we can focus on a set of puzzling "thought experiments" - imagined scenarios where innocent-looking steps lead us to philosophical worries - to zero in on what's at issue. And while not every philosopher agrees that the thought experiments carry great meaning, all can agree that something must be said to explain the puzzlement they generate. What's more, much of the contemporary literature on the philosophical problem of consciousness at least touches on some or all of these imagined scenarios, so they are needed background knowledge for anyone wanting to go down this particular rabbit hole.

The Knowledge Argument

The first thought experiment is called the "knowledge argument" against physicalism (Jackson 1982). Physicalism is the claim that everything is ultimately made of physical stuff like atoms and nothing else. Physicalism is a central feature of the standard scientific worldview of today. The knowledge argument seems to show that consciousness cannot fit into that worldview. The thought experiment brings out an everyday intuition that many of us have before we get near a philosophy classroom. Intuitions are generally unarticulated beliefs or gut feelings we have about certain subjects. For example, most people feel it's wrong to kick a puppy, even if we can't really justify why that is. A key job of philosophy is exposing these underlying intuitions and investigating whether they're to be kept or thrown out as we develop a deeper understanding of a subject. The everyday intuition brought out by the knowledge argument is the idea that a person blind from birth will never really know all that sighted folk know about colors. A blind person might ask us to describe red. We can say things like "it's a feature of objects which can vary independently of shape." The blind person might say, "Oh, you mean like texture!" But we'd have to say that's not it. We might say, "Red is hot, like the sound of a trumpet." But we'd quickly recognize that there's something we can't put into informative words, something that's left out of any description we offer to our blind friend. That left-out something, whatever it is, is a key element in the problem of consciousness.1

The knowledge argument takes this intuition and makes a more general point about the limits of physicalism and the scientific worldview. Instead of imagining (or actually talking to!) a blind person, we are asked to imagine a super-scientist of the future. She lives in a time when all the outstanding problems of science have been solved. What's more, she has a prodigious memory and an unfailing ability to digest and understand science. In fact, she has gone through all the relevant material and knows all of the facts of a completed science. But this super-scientist - let's call her Mary, following Frank Jackson who introduced this story in 1982 - has been brought up in a very special environment. Everything in her world is black and white and shades of grey (perhaps this is achieved by fitting her with special lenses which make the world look like it does on a black-and-white TV set). She has never in her life seen colors. Now for the crucial intuition-tapping question: when she's finally released from her black-and-white captivity and sees a red rose for the first time, does she learn anything new? Most of us would say that she does learn something new. She learns that this is what red looks like, that this is what it's like for one to see red. This seems like a fact she couldn't have known beforehand. But given that she already knew all of the facts of science, this must be a fact beyond the reach of science, something left out of science altogether! So there are facts beyond the scientific worldview. And since science plausibly contains all the facts about physical stuff - where all the atoms are, how they interact, and so on - this new fact must be about something that isn't physical. So physicalism, which claims that, ultimately, all the facts are physical facts, must be incorrect.

And what does this tell us about consciousness? When we think about it, the fact that Mary doesn't know before her release is a fact about her (and others') experience. It is a fact about what it's like to see red from the inside. She already knows all the "outside" facts about red: that it's feature of the surfaces of some physical objects, that such surfaces reflect light at certain wavelengths, and so on. She even knows, in neurological terms, what happens in normal observers when they see red: cone cells on their retinas fire in a particular ratio, activity occurs in area V4 of their brains, and so on. But none of these scientific facts helps her to know what it's like to experience red. That is a fact about conscious experience. There's a special quality there - the "redness" of red. Philosophers label these sorts of special qualities of consciousness "qualia." Mary lacks knowledge of red qualia. And no amount of scientific information can give her that knowledge, or so it seems. There is clearly something special about conscious experience.

So are we any closer to figuring out just what the problem of consciousness is all about? From the knowledge argument, we can see that consciousness possesses special qualities, and these qualities seemingly defy description. If you haven't experienced them yourself, no amount of what philosopher David Lewis calls "book learning" will tell you (Lewis 1988). And as philosopher Ned Block says, channeling Louis Armstrong, "if you gotta ask, you're never gonna know!" (Block 1978). And if qualia can't be informatively described, then they can't be explained scientifically, or so it seems. We are left with a hard problem! Now, not all philosophers agree with this bleak assessment of consciousness, but it's hard to deny that there at least appears to be an explanatory puzzle here. Throughout this book, we'll consider a range of responses to the problem, from those who accept the knowledge argument and try to sketch out what must be added to our worldview to fit in consciousness, to those who argue that the argument is misleading, inconclusive, or completely invalid. Those theorists have to explain why it is that consciousness prima facie poses a problem and then explain where consciousness fits in the current physicalist worldview. But all that matters so far is that we begin to get a feel of the philosophical worry here. A second thought experiment may help to bring that worry out further.

Zombies!

This thought experiment asks us to imagine, if we can, a creature just like us in all physical respects, right down to the last atom, but lacking consciousness (Chalmers 1996). Could you, for example, have a perfect physical doppelgänger, a molecule-for-molecule twin, who nonetheless fails to be conscious? This sort of nonconscious physical twin is called a "zombie" by philosophers. Unlike the zombies in monster movies, these "philosophical zombies" look exactly like us from the outside. But inside "all is dark" - there is no experience at all. Consider that many of the tasks we perform repeatedly in a day can become automated, so that we can do them on "auto-pilot." For example, if I have to wash the dishes (a task I perform many times a week at our house!), I may become so lost in...