I’ve spent, compared to most people I know, a lot of time in the woods — not just in the wilderness, but in the woods specifically. Temperate deciduous forest constitutes almost the entirety of Pennsylvania and New York and New England where I spent my summers growing up. I’ve spent a lot of time in the woods.
In the woods there are black bear and panthers and grey wolves. In the woods there are copperheads and rattlesnakes. In the woods there are fires and in the woods there are floods. In the woods I’ve found there are many things that can hurt me, but not many things that can scare me.
One time, in the woods of northern Maine — about twenty miles west of Millinocket — I was scared. It was a clear and windless day. I was down in a gulley, standing in a muddy track that had been a brook, before the spring melt dried up. A light breeze came up, sighing through the ferns, and the whole world was a rustle.
From above me, I heard a creaking and groaning. On the ridgeline, an eighty-foot silver maple swayed left and swayed right. There was a crack like a deer rifle. The silver maple slipped off its stump and pitched forward. The trunk and the boughs and the branches and the twigs fell through space while most of the red and gold leaves stayed where they had been, floating. The twenty-ton corpse came crashing to the forest floor before sliding and skidding down the gulley, throwing stones and saplings in its wake. Half the boughs tore away and the leaves fluttered in the cool air. I remember standing still for a long time in what had been a brook. I remember feeling scared. And, of course, I remember hearing a sound.
This was, then, a roundabout way of saying: If a tree falls in a forest, and some one is there to hear it, it seems to make a sound.
“But that’s just like, your opinion, man.” — The Dude, The Big Lebowski
If a tree falls in a forest and no one is there to hear it, does it make a sound? The question was probably inspired by George Berkeley, the eighteenth century Irish philosopher who advanced the theory of immaterialism. The question — or a question close to it — was first asked in June 1883 in The Chautauquan, which asked, “If a tree were to fall on an island where there were no human beings would there be any sound?” The magazine answered, “No. Sound is the sensation excited in the ear when the air or other medium is set in motion.” A year later, Scientific American asked, “If a tree were to fall on an uninhabited island, would there be any sound?” The magazine answered, “Sound is vibration, transmitted to our senses through the mechanism of the ear, and recognized as sound only at our nerve centers. The falling of the tree or any other disturbance will produce vibration of the air. If there be no ears to hear, there will be no sound.” Both of these magazines considered the question technically, focusing on a strictly scientific viewpoint instead of considering the philosophical one. But where’s the fun in that?
Berkeley, however, would probably deny that there was an unperceived tree in the first place. Berkeley — like so many of his contemporaries — managed to sum up his philosophy in a neat latin phrase: esse est percipi (aut percipere); to be is to be perceived (or to perceive). And so, in the contrapositive: if the tree is not perceived, then the tree is not. If you asked George Berkeley, “If a tree falls in a forest and no one is there to hear it — ” he would probably cut you off at that point, asking, “What tree?”
But what does this mean for Gilbert Harman’s brain in a vat? In the thought experiment a supercomputer uses electrical impulses on a disembodied brain (in a vat) to simulate reality so that the mind might experience similarly to an embodied brain, but independent of any events in the real world. (It should be noted that this thought experiment relies on a materialist understanding of the universe as presented by Baron d’Holbach.) When this thought experiment is juxtaposed with the question of the tree, it only raises more questions.
To begin, the issue of being a brain in a vat relies entirely on materialism, while the issue of an unperceived tree relies entirely on immaterialism. In the case of a brain in a vat, we encounter the possibility of experience without reality. In the case of the unperceived tree, we encounter the possibility of reality without experience. And we can’t have it both ways. But which allows for a more certain epistemological ground? Which provides us an Archimedean point on which to build our understanding of the world? Is it better — as Berkeley tried — to deny any gap between intramental and extramental reality so that we might refute skepticism by abandoning the unperceived tree? Or is it better to hold that an unperceived tree exists while admitting the skeptical possibility that trees right in front of us might not actually be there.
I don’t know which of these options is preferable, and I don’t know if an option being “preferable” should make it true. But I know that these are important questions. What’s at stake? Everything. But, let’s return to the question: If a tree falls in a forest and no one is there to hear it, does it make a sound? Albert Einstein once asked his friend and fellow physicist Niels Bohr if “the moon does not exist if nobody is looking at it.” Bohr replied that, however Einstein may try, he could not prove that the moon does exist. This elevates the entire riddle to the status of infallible conjecture — one that cannot be either proved or disproved.
(In metaphysics, this question brings two theories to a natural competition. Substance theory stipulates that a substance is distinct from its properties, while bundle theory considers an object to merely be its sense data.)
At any rate, I’m not sure what I believe — but I’m sure that I can’t be sure, and that’s something, right? But I’m sure of my perception. Bring it back to those northern woods, all those years ago. I don’t know if there was a tree. But I know I heard a tree. And I know I was afraid.