Philosophy of Mind

A Beginner's Guide

Edward Feser

• Publisher: Oneworld Publications
• Year: 2006
• ISBN:
  9781780740416
• Topic: Philosophy
• Subtopic: Philosophy History & Theory

In this lively and entertaining introduction to the philosophy of mind, Edward Feser explores the questions central to the discipline; such as 'do computers think', and 'what is consciousness'; and gives an account of all the most important and significant attempts that have been made to answer them.

1

Perception

You’ve just started reading this book. Or so you think. But are you certain that you’re really reading it? How do you know you’re not merely dreaming that you’re reading a book, or having a vivid hallucination? How do you know that you’re not in fact trapped in an extremely sophisticated virtual reality computer program, like the characters in the film The Matrix?

Perhaps you’re tempted at this point to stop reading, convinced that such questions are frivolous, suitable maybe for late night sessions over a few beers but not for a book of serious philosophy, which is what you had hoped you’d bought. Yet there was no more serious a philosopher than René Descartes (1596–1650) – the very father of modern philosophy, as he is widely known – and he took these questions (minus the Matrix reference, obviously) to be of profound significance, for they formed, in his view, the starting point of a line of inquiry that not only lays the foundation for scientific knowledge, but also reveals the true nature of the human mind and its relationship to the material world, culminating in nothing less than the establishment of the immortality of the soul. As we will see, philosophers disagree over whether Descartes was right to think these things. But few would deny that his arguments are powerful and as worthy of consideration today as they were when he first put them down on paper. Nor can it be denied that, whatever one ultimately thinks of Descartes’s views, they have set the agenda for modern philosophy in general and philosophy of mind in particular. For these and other reasons, we will do well to have made his starting point in the study of the mind our own.

So, your curiosity now piqued, let’s return to this question that Descartes thought has such deep implications: How do you know you’re really reading this book?

Dreams, demons, and brains in vats

No doubt your first inclination is to say that it’s just obvious that you’re reading it, since, after all, you can see it in your hands, feel its pages, smell the ink and hear your fingers slide across the paper. Were you so inclined, you would also be able to taste the chemicals in the paper and ink. In any case, your reason for believing that you’re reading the book is that you’re having just the sorts of experiences you’d expect to have while reading. Your senses tell you you’re reading the book; therefore, you must be reading it.

There is a problem with this answer which can be seen by comparison with the following example. Suppose Fred tells you that there will be a party at Ethel’s house this Saturday, and that you know Fred to be a frequent and very convincing liar. Sometimes he tells the truth, but very often, even when the subject matter is trivial, he does not; in either case, his demeanor is exactly the same, and it always appears very sincere. Given that Fred is your only source for this information, do you have strong grounds for believing that there will indeed be a party at Ethel’s this Saturday? Surely not. You just don’t know for certain, because your only evidence for this belief – Fred’s word, with all its evident sincerity – would be exactly the same whether there really will be a party or not.

We are, it seems, in exactly this sort of situation with regard to our senses. They “tell” us things all the time, and their way of telling us is very convincing – “seeing is believing,” as the saying goes, for it is hardest to doubt something precisely when it seems to be there right before your eyes. Yet for all that, there are well-known cases where what our experiences tell us is real is not real at all. You may have had the experience of being chased by a knife-wielding murderer, your heart pounding and a scream welling up in your throat. Terrified, you reflected on how much it all seemed like a nightmare, but being so vivid, it couldn’t be; and then, just as the knife was set to plunge into you ... you woke up. You thought your senses were telling you that your life was in imminent danger, but you were wrong. In fact, you couldn’t have been more safe, snug as you were in bed, asleep and dreaming.

But if your experiences could, in dreams, deceive you in a matter so momentous, why not in a matter as trivial as reading a book? Indeed, you know that they very often do deceive you in trivial matters – in every humdrum, murderer-free dream you have. So how can you be sure you’re not dreaming right now? “But this is too vivid to be a dream!” you might reply. Yet, as I’ve already hinted, a dream can sometimes be so vivid that the person having it explicitly thinks, during the dream, that it isn’t a dream. Perhaps this is one of those dreams. Besides, how do you know reality is always more vivid than a dream? On the basis of your memory of past dreams? But how do you know you aren’t just dreaming that you’re remembering those past dreams correctly? A similar problem afflicts any appeal to how one’s dreams normally are – in black and white, say. For how can you be sure those memories are accurate? (And why couldn’t this just be your first dream in color? There’s a first time for everything, after all.) Nor will an appeal to evidence on the nature of dreams from psychology textbooks and the like help – maybe you’re just having false dream “memories” that you ever read such books. In fact, it seems any evidence you could appeal to, or any test you could perform to prove you’re not dreaming (for example, pinching yourself) is evidence or a test you might just be dreaming you’re appealing to.

The bottom line is this: there is nothing in the nature of your experiences themselves that can tell you one way or the other whether they are waking or dreaming – in which case, experience, by itself, cannot tell you whether what you’re experiencing right now (and at any time you consult it) is real. Nor are dreams the only basis for this disquieting conclusion. It is widely known that our experiences, in all their varieties – visual, auditory, tactile, gustatory, and olfactory – depend on processes within our brains. When, for example, you see a lemon, that is a result of light reflected from the lemon striking your retinas, which causes signals to be sent, via your optic nerves, to more central processing centers in the brain; which neural activity ultimately gives rise to your visual experience of the lemon. But if that is the natural way in which the experience of a lemon is produced, it is easy to see how such an experience might, in principle, be produced artificially – a neurosurgeon could simply stimulate directly the portion of your brain that causes the experience, bypassing the processes in the optic nerve, etc. that would normally trigger events there. Indeed, neuroscientists are even now capable of producing very simple sensations – a flash of red in one’s visual field, say, or the smell of lilacs – by such stimulation.

If that is possible, it would also seem to be possible for the entire stream of one’s conscious life to be produced artificially. We can imagine that neuroscientists might hook someone’s brain up to a massive virtual reality supercomputer which stimulates the brain to have just the sorts of experiences that characterize normal everyday existence. But then, how can you know that you yourself aren’t at this very moment hooked up to such a computer? You feel sure that you are reading a book, but maybe you’re really just a disembodied brain, floating in a vat of nutrients in a laboratory somewhere, the subject of a bizarre experiment by some mad neuroscientists who are causing you to have the experience of reading a book – along with all the other experiences you are now having or have ever had. Perhaps they are chuckling at this very moment at how amusing it is to have just given you the experience of reading about them!

It was Descartes who introduced the “dream argument” into modern philosophical discussion, and though he did not discuss the “brain-in-a-vat” scenario he did also present another, perhaps even more chilling, possibility. You might find it reassuring to think that even if you are really dreaming at this moment or are a disembodied brain hooked up to a virtual reality machine, this would still all occur in the context of a physical environment that exists independently. Perhaps you can’t know what exactly is going on in it at any given moment, but at least it is there – at least, that is, there is a bed you’re sleeping in right now, or a laboratory somewhere with chuckling mad scientists. But what if not even all of that were real? What if you were nothing but a disembodied soul, with no physical body or brain at all, and the only other thing that exists is an extremely powerful evil spirit, a demon, who spends its time putting into your mind all the experiences and thoughts you’ve ever had? Every place you think you’ve ever been, every person you think you’ve ever met, the physical universe itself – none of it is real, just a massive, ongoing hallucination. How could you prove this isn’t what is happening to you? As with the dream scenario, it seems you could have no evidence that it isn’t – for any evidence you appeal to could be evidence the demon itself has manufactured.

Descartes took arguments of this sort to tell us something important about the nature of perception, namely that there is a gap – potentially, at least – between the appearance of the world that it presents to us, and the reality outside. In perception we know that appearance immediately and intimately; what we know of the reality is another, and more problematic matter. The first and most obvious consequence of this is epistemological, that is, it concerns the nature of human knowledge. That consequence is, in Descartes’s view, not (as it might at first seem to be) that we can’t know anything for certain, but rather that what we do know for certain, indeed, whatever it is we know at all, can’t ultimately come directly from perceptual experience alone. In this Descartes is opposed to empiricism – the view that all knowledge does ultimately rest on the senses – and also, perhaps, to common sense, which holds that whether or not the senses form the basis of all knowledge, they do at least give us all by themselves some indubitable knowledge. Descartes held that the sorts of arguments just considered prove that this can’t be right. The senses by themselves are in fact so feeble that they can’t even tell us whether we’re awake. If we do have knowledge, then (and Descartes thought we surely did) it must come from somewhere else, namely from pure reason operating independently of the senses, a view about the basis of knowledge known as rationalism.

The first thing you know on this basis, according to Descartes, is that at least you exist. How? Well, even if you really are dreaming right now, are a brain in a vat, or the victim of a deceiving evil spirit, you still must exist in the first place in order to do the dreaming or to be deceived. Indeed, if you’re worrying about whether or not you’re dreaming, whether there’s such a demon, or whether you even exist at all, you must exist in order to do the worrying. If you didn’t exist at all, obviously you wouldn’t be around to worry about the fact. So just to think about whether you exist is enough to prove that you do. “Cogito, ergo sum,” as Descartes put it – “I think, therefore I am.” This famous argument, knowable without having to rely on the trustworthiness of the senses, is in Descartes’s view the starting point of all knowledge and the absolute stopping point of all doubt: if you can know nothing else, you can at least know for certain that you are real.

So far so good; but is anything else real? In particular, is the physical universe you’ve always assumed existed outside your mind – the mundane world of tables, chairs, rocks, trees, other human beings, dogs, cats and other animals, planets, stars and galaxies – is all that real too? It might seem that if all your perceptual experiences could be false, then there just is and can be no way to know that anything else exists. Perhaps nothing else does in fact exist – not even an evil spirit or mad scientists. Perhaps you are the sole reality, your perceptual experiences constituting nothing more than an indefinitely long hallucination and the entire universe a figment of your imagination. This is solipsism: the view that “I alone exist.”

Indirect realism

Descartes himself was no solipsist. He was a staunch realist, who firmly believed that the world of external, objective, physical objects exists and that, even given arguments of the “dreaming” and “evil spirit” sort, we really can, through our senses, know that world. But he also thought that these arguments show that we don’t know it directly. What we do know directly are the contents of our own minds, the rich stream of experiences that constitutes everyday conscious life. The physical world that is represented by those experiences, not mad scientists or demons, is indeed what normally causes us to have them, but the experiences themselves are all we have immediate access to. It is as if we are watching images on a television screen, without being able directly to observe the ultimate source of the images. We might suppose that what we’re seeing is a live broadcast of astronauts inside a space shuttle orbiting the earth, and we may well be right – but it’s at least possible that what we’re really seeing is a recording of events that occurred earlier, actors on a sound stage in Hollywood and some clever special effects, or even an entirely computer-generated image. No doubt we can find out through some independent source whether it really is a live broadcast, but the fact that we can’t know this just from observing the images shows that we do need such a source and that what we do see directly cannot be the astronauts themselves, but only a representation of them. Similarly in perception, on Descartes’s view: when a book really is out there and is what’s causing you to have a “bookish” experience, then you really are seeing it, though indirectly; when it’s a dream or virtual reality device or demon causing the experience, you’re not seeing it at all. Either way, what you “see” directly is never the book itself but only a perceptual representation of the book.

This view, that all we are ever immediately aware of is the “veil of perceptions” that constitutes our conscious experiences, is known variously as indirect realism, representative realism, or causal realism – “realism” because it holds that there really is a physical world existing outside our minds, “indirect,” “representative,” or “causal” because it holds that we know that world only indirectly, through our direct awareness of the perceptual representations that world causes us to have, via its impact on our sensory organs. A long line of famous philosophers, including empiricists like John Locke (1632–1704) and Bertrand Russell (1872–1970) – otherwise in disagreement with Descartes over the latter’s rationalism – have held this view, usually on the basis of examples less bizarre than the ones we’ve considered thus far.

One such example would be hallucinations, which can seem indistinguishable from the normal perceptual experiences which present us with a reliable picture of the external world (that is, experiences which are, as philosophers say, veridical). The hallucination of a dagger in one’s hand could be as vivid as really seeing and feeling it there. There might be nothing in the experiences themselves that tells you whether they are trustworthy, and this supports the notion that whatever one is directly aware of in the one case must be the same sort of thing as what one is directly aware of in the other, since otherwise there would plausibly be some difference in the intrinsic character of the experiences. But in the case of hallucinations, it obviously can’t be an external physical object that one is directly aware of. So neither can an external physical object be what one is directly aware of in the case of a veridical perceptual experience. But then what one is directly aware of must be something else – a perceptual representation in the mind.

There is also the matter of the causal relations existing between perceptual experiences of physical objects and the objects themselves. There is, as implied above, a surprisingly long chain of causes involved in even so simple an experience as the seeing of a lemon. Certain wavelengths of light are reflected off the surface of the lemon, photons travel to your retinas, rods and cones are stimulated and send signals along the optic nerve, these activate neural pathways in the brain that make their way to the occipital lobe, and after a further flurry of activity the experience finally happens. So how can your awareness of the lemon fail to be indirect, with all these intermediate steps existing between that awareness and the lemon itself? Moreover, such a sequence of causes occurs over time. In the lemon case, the light reaches your eyes virtually instantaneously, but in the case of looking at the sun, the light takes a full eight minutes to reach your eyes, meaning that what you’re seeing now is the sun as it appeared eight minutes ago. The light from the star Alpha Centauri takes over four years to reach us, and light from other celestial objects takes much longer – in many cases, so long that some of the objects we see in the night sky no longer exist! So, again, how could your awareness of these objects fail to be indirect? How could you be directly aware of something that might not even exist?

These considerations regarding hallucination and causation arguably supply, all by themselves – with no need for an appeal to bizarre suggestions about mad scientists or evil spirits – powerful support for the indirect realist view of perception. As the philosopher Howard Robinson has suggested, they are best combined into a single simple and powerful argument, which we can summarize thus:

1. By stimulating the brain so as artificially to produce a neural process that is normally associated with a certain veridical perceptual experience, it is possible in principle to bring about a hallucination that is subjectively indistinguishable from that experience.

2. But if the immediate causes of veridical perceptual experiences and their hallucinatory counterparts are of the same sort, then these effects must be of the same sort as well.

3. In the case of hallucinations, the effect is obviously direct awareness not of any external physical object, but rather of a subjective mental, perceptual representation of an external object.

4. So in the case of veridical perceptual experiences too, what one is directly aware of must be a subjective perceptual representation.

Again, this is not to deny that in veridical perceptions you really do perceive external, objective, independently existing physical objects. It’s just that you perceive them only indirectly, through your direct awareness of something subjective and mental. You do indeed really see the lemon, but only on the priva...