A Tree Falls

In his discussion of the science of color, Steve Palmer pointed out that the problem with color is “reminiscent of the old puzzle about whether a tree that falls in the forest makes a sound if nobody is there to hear it.” Vision Science p. 95. He’s right. Color and sound would be considered paradigm secondary qualities, if anything is.  In the mind-independent physical world is light and air, through which waves travel. The waves are not colored or noisy. We decode the frequency of these waves as color and sound—as long as the frequencies are within the range we can cope with.

In his book Philosophy of Mind (3rd Edition, Routledge 2013), John Heil uses that old tree as his way of introducing his subject. One advantage of discussing sound, rather than the far more frequently mentioned color, is that the physics of sound are much easier to grasp than the physics of light. Heil does a very nice job and we hope he won’t mind if we quote him at some length, and kibitz a little.


Experience and reality

Does a tree falling in the forest make a sound when no one is around to hear it? The question is familiar to every undergraduate. One response is that of course the tree makes a sound – why shouldn’t it? The tree makes a sound whether anyone is on hand to hear it or not. And in any case, even if there are no people about, there are squirrels, birds, or at least bugs that must hear it crashing down.

BQTA: sound will end up in the mind, but Heil’s first point if that not everything is in the mind. The falling tree sends out shock waves through the air. Those variations in air pressure are out there whether any humans are around or not. Those vibrations will affect the bodies of any animals in the vicinity. Whether bugs experience the vibrations as sound is anybody’s guess.

Consider a more measured response, versions of which have percolated down through successive generations of undergraduates. The tree’s falling creates sound waves that radiate outwards in a spherical pattern. If these sound waves are intercepted by a human ear (or maybe – although this might be more controversial – the ear of some nonhuman sentient creature) they are heard as a crashing noise. If the sound waves go undetected, they eventually peter out. Whether an unobserved falling tree makes a sound, then, depends on what you mean by sound. If you mean ‘heard noise’, then (squirrels and birds aside) the tree falls silently. If, in contrast, you mean something like ‘distinctive spherical pattern of impact waves in the air’, then, yes, the tree’s falling does make a sound.

BQTA: calling the waves “sound waves” is quite natural. The issue, however, is the distinction between 1) variations in air pressure, which are out there quite apart from any observers, and 2) the sensation of sound, which is only in the mind, correlated with the appropriate NCCs.

Most people who answer the question this way consider the issue settled. The puzzle is solved simply by getting clear on what we mean. Indeed, we can appreciate the initial question as posing a puzzle only if we are already prepared to distinguish two senses of ‘sound’. But what precisely are these two senses? On the one hand, there is the physical sound, a spherical pattern of impact waves open to public inspection and measurement – at any rate, open to public inspection given the right instruments. On the other hand, there is the experienced sound. The experienced sound depends on the presence of an observer. It is not, or not obviously, a public occurrence: although a sound can be experienced by many people, each observer’s experience is ‘private’. We can observe and measure agents’ responses to experienced sound, but we cannot measure the experienced sound itself. This way of thinking about sounds applies quite generally. It applies, for instance, to the looks of objects, to their tastes, their smells, and to the way they feel. Physicist Erwin Schrodinger (1887-1961) puts it this way:

The sensation of colour cannot be accounted for by the physicist’s objective picture of light waves. Could the physiologist account for it, if he had fuller knowledge than he has of the processes in the retina and the nervous processes set up by them in the optical nerve bundles and in the brain? I do not think so. Mind and Matter 1958

The picture of the universe and our place in it that lies behind such reflections has the effect of bifurcating reality. We have, on the one hand, the ‘outer’ material world, the world of trees, forests, and sound waves. On the other hand, we have the ‘inner’ mental world, the mind and its contents.

The mental world includes conscious experiences: the looks of seen objects, ways objects feel, heard sounds, tasted tastes, smelled smells. The ‘external’ material world comprises the objects themselves, and their properties. These properties include such things as objects’ mass and spatial characteristics (their shapes, sizes, surface textures, and, if we consider objects over time, motions and changes in their spatial characteristics).

Following a long tradition, we might call those observed qualities properly belonging to material objects ‘primary qualities’. The rest, the ‘secondary qualities’, are characteristics of objects (presumably nothing more than arrangements of objects’ primary qualities) that elicit certain familiar kinds of experience in conscious observers. Experience reliably mirrors the primary qualities of objects. Secondary qualities, in contrast, call for a distinction between the way objects are experienced and the way they are. This distinction shows itself in our reflections on the tree falling in a deserted forest. More fundamentally, the distinction encourages us to view conscious experiences as occurring ‘outside’ the material universe.

BQTA: “outside” the material universe means “inside” the mind. The primary qualities are the ones which are properties of things in themselves. Things like mass, spin, charge, solidity, motion, extension, texture, shape, structure. These are outside the mind, in public. The secondary qualities are produced in our minds by the effects of certain primary qualities. It’s the shape and motion of the air vibrations that we decode as sound. Heil extends what’s inside the mind to include “the looks of seen objects.” That would mean that everything we perceive is mind-dependent.

You might doubt this, confident that conscious experiences occur in brains, and regarding brains as respectable material objects. But now apply our distinction between primary and secondary qualities to brains. Brains – yours included – have assorted primary qualities. Your brain has a definite size, shape, mass, and spatial location; it is made up of particles each with a definite size, shape, mass, and spatial location, and each of which contributes in a small way to the brain’s overall material character. In virtue of this overall character, your brain looks (and presumably sounds, smells, feels, and tastes!) a particular way. This is just to say that your brain can be variously experienced. The qualities of these experiences, although undoubtedly related in some systematic way to the material reality that elicits them, differ from qualities possessed by any material object, including your brain. But if that is so, where do we situate the qualities of experience?

Your first instinct was to locate them in the brain. But inspection of brains reveals only familiar material qualities. An examination of a brain –even with the kinds of sophisticated instrumentation found in the laboratory of the neurophysiologist and the neural anatomist – reveals no looks, feels, heard sounds. Imagine that you are attending a performance of Die Walküre at Bayreuth. Your senses are assaulted by sounds, colors, smells, even tastes. A neuroscientist observing your brain while all this is occurring would observe a panoply of neural activities. But you can rest assured that the neuroscientist will not observe anything resembling the qualities of your conscious experience.

The idea that these qualities reside in your brain, then, appears unpromising. But now, if the qualities of your experiences are not found in your brain, where are they? The traditional answer, and the answer that we seem driven to accept, is that they are located in your mind. And this implies, quite straightforwardly, that your mind is somehow distinct from your brain. Indeed, it implies that the mind is not a material object at all, not an entity on all fours with tables, trees, stones – and brains! Minds appear to be nonmaterial entities: entities with properties not possessed by brains, or perhaps any material object. Minds bear intimate relations to material objects, perhaps, and especially intimate relations to brains. Your conscious experiences of ordinary material objects (including your own body) appear to reach you ‘through’ your brain; and the effects your conscious deliberations have on the universe (as when you decide to turn a page and subsequently turn the page) require the brain as an intermediary. Nevertheless, the conclusion seems inescapable: the mind could not itself be a material object.

The unavoidability of the philosophy of mind

You may find this conclusion unacceptable. If you do, I invite you to go back over the reasoning that led up to it and find out where that reasoning went off the rails. In so doing, you would be engaging in philosophical reflection on the mind: philosophy of mind. Your attention would be turned not to the latest results in neuroscience, but to commonsense assumptions with which this chapter began and to a very natural line of argument leading from these assumptions to a particular conclusion. As you begin your reflections, you may suspect a trick. If you are right, your excursion into philosophy of mind will be brief. You need only locate the point at which the trick occurs.

I think it unlikely that you will discover any such trick. Instead, you will be forced to do what philosophers since at least the time of Descartes (1596-1650) have been obliged to do. You will be forced to choose from among a variety of possibilities, each with its own distinctive advantages and liabilities…

Some readers will be impatient with all this. Everyone knows that philosophers only pose problems and never solve them. [Here at BQTA, we value good questions.] Solutions to important puzzles reside with the sciences. So it is to science that we should turn if we ever to understand the mind and its place in a universe of quarks, leptons, and fields. Residual problems, problems not susceptible to scientific resolution, are at bottom phony pseudo-problems. Answers you give to them make no difference; any ‘solution’ you care to offer is as good as any other.

Although understandable, this kind of reaction is ill-considered.

BQTA: some important philosophers have seriously considered that reaction. And figuring out why relying solely on science is ill-considered is not easy.

In any case, we have little choice. Philosophical questions about the mind will not go away. They occur, even in laboratory contexts, to working scientists. And as recent widely publicized controversies over the nature of consciousness, ignoring such questions is not an option.


sequoia 1917 RvOjilx.jpg
100 years ago, camping on a fallen sequoia 1917

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