I’m the last person I know of who took slides. I stopped only about ten years ago. I’ve suffered a lot of good-natured ridicule over my habit, especially when I used to show slides of my kids or of trips. But I just couldn’t see how anyone could prefer dull inks on a 4"x6" card over the bright colored beams of light shining on a screen 150 times as large. And the resolution was astonishing! As large as I ever made the projection of one of my slides, I never detected any graininess.
I’ve been thinking a lot lately about a slide I took in the museum atop the Acropolis in Athens, a picture of a bas relief of a boy leading a cow. I stared and stared at that sculpture for a long time, unable to shake the nagging question: Is it really there? Weird question, I know. Maybe not so weird, though, right after a semester of seventeenth- and eighteenth-century philosophy at the University of Iowa. Empirical philosophers like Locke and Hume said that although everything we know comes through our senses, our senses are cheats (Who could have guessed that I’d allude to A Christmas Carol two posts in a row? Okay, it’s not really all that unlikely.) As I was saying, your senses are cheats. You could be dreaming. You could be hallucinating. Even if you’re in your right, wakeful mind and the thing is truly there, you don’t actually know what it looks like. You think you know what a circular table looks like, for instance, but you always only see one side of it at a time. And the top almost never actually appears as a circle, unless you’re looking at it from straight above. You may think of it as a circle, but try drawing a true circle on a piece of paper with some legs under it, and you’ll find that what you drew doesn’t look like anything in reality. You don’t know what color the table is, either, since it looks black in one kind of lighting and gray in another. You don’t even know what size the table is, since it appears smaller when you’re farther away. You don’t actually see a table, the empiricists concluded. You see a constantly changing series of images in your mind. What you see are only “ideas.” Whether or how those ideas correspond to a table, you can’t know.
Twenty-seven years later, I’m wondering why that professor couldn’t have had us read some Thomas Reid in that class. Reid was the chief figure in Scottish Common Sense philosophy and wrote mainly in response to Hume, who argued that besides not knowing if the table exists, I couldn’t even know if the “I” that I imagine seeing the (imaginary) table exists. Reid’s solution to the problem posed by Hume boils down, in my mind at least, to two very effective arguments.
First, Reid says, You empiricists claim that when I think I see a table, I actually only see an idea in my mind. In other words, that image of an ellipse with four legs in my mind is the true object of an action of my mind called “seeing,” an act that has nothing to do with my eyes. But every day common sense tells us that the image itself is the action of my mind and that the object of that action is a table existing in reality outside my mind. You argue as if the burden is on me to prove the existence of the table outside myself. But I say that your theory posits new things for which you have no evidence. So the burden of proof is actually on you empiricists to show us the image in the mind as an existing object. Where and how does this happen in the brain? And what is this action called “seeing” that is separate from the image of the table? My senses give me continuing evidence of the existence of the table, but you give me no evidence of the existence of an extra act of the mind that “sees” an image in my mind.
This argument took all the wind out the empiricists’ sails for me. Like the table seen from a great distance, their nagging skepticism suddenly seemed very small. But I still wanted some positive indication that the table (and the bas relief) existed, and this Reid gave me a few chapters later. All the talk about the changing perspective of the table as we move around, he points out, far from telling us to doubt our senses and the existence of the table, shows us exactly the opposite. Of course we can never see the whole of the table at once. But the principles of geometry predict what aspect we will see, what apparent size it will take on, and what angles and shapes will appear to us in representation of the circular table. And since our changing perspective follows those geometrical predictions exactly every time we move, we have overwhelming, consistent evidence that the images all result from the sight of an actual table with one given shape and determinable dimensions.
If you’ve never read Descartes or Locke or Hume, you may be experiencing a bout of a different kind of skepticism right now: you may have trouble believing that such thoughts had ever troubled me or that I could ever have doubted the existence of a particular sculpture in the Acropolis museum. But I have read those philosophers, and their arguments stuck with me. I had some ripostes in mind: some I had read in other places and some I had concocted on my own. But Thomas Reid’s response has surpassed them all. I wish he were here so I could shake his hand and thank him. And I wish my philosophy professor were here so I could shake his hand and tell him to include Reid in his class.
To go back to the Acropolis, my response to my doubts about that sculpture didn’t make much sense, now that I think about it. I tried to capture an elusive material being by recording some light waves on film. Then I developed the film and shined a projector light through the slide, casting the colors on a screen, which reflected the colored light into my eyes. And now I have the slide digitized. So when I look at the picture these days, I’m seeing the representation on a computer screen of a series of magnetic polarities set by scanning the light shining through a slide developed from film exposed to the light reflecting off of a bas relief sculpture of a boy. So I’m several steps removed from that sculpture. But at least I now believe the sculpture exists.
At least it did in 1987 when I last saw it with my own eyes.