This thread is going to talk about Perception, how our senses work, and some related topics. David Kelley has written a book called the Evidence of the Senses, and I'll try to present some of what he says. It's a real academic book, so unless you're really, really interested, don't bother.
The reason we start with perception is that it's the source of all of our knowledge about reality. It is our link to the real world. It's what keeps us honest. And because of that, it's also been attacked viciously by the opponents of reason. If you can invalidate the senses, you throw everyone into an imaginary world where anyone's thoughts or ideas are just as good as anyone else's.
One crude argument against the senses is that we have the ability to hallucinate. Sometimes we think we're seeing something when we're not. Dreams are one kind of example. Another is if you're on some kind of drug or something. A related example is an illusion. You could have illusions done by magicians. You could have optical illusions, like shoving a broom handle into a pool of water and seeing that it looks bent. These are all given as evidence that our senses are flawed.
There are a few Objectivist rebuttals to this kind of argument. The hallucination argument is flawed for a couple reasons. First, how do they know it didn't really happen? They count on the evidence of the senses in order to show that the hallucination was incorrect. For instance, they could video tape you in a room while on some drug, and show you the evidence afterwards that it didn't happen. But they have to rely on the senses in order to give some semblance of sanity to this proof.
In general, hallucinations are caused by some kind of problem with the brain. It's similar to dreams though. Would we take anyone seriously who thought his dreams were the same as reality? Even children can tell the difference. But they count on you not to be able to explain the difference.
Next, how do you know the broom handle didn't really bend? You know because of the evidence of the senses. The people trying to invalidate them are counting on their validity to make the point. That is enough to invalidate their argument. But we can go further. We know the light waves are bent by refraction, and we can actually see this happening in a laboratory. The people arguing against the validity of the senses know this, and even use this information as part of their proof. They say that your perception is wrong. That you're mis-perceiving it.
Now this brings us to one of the main thrusts of Kelley's book. The senses provide us information, but we interpret the information. The fact that we perceive the same thing in different ways due to different context doesn't invalidate our senses. On the contrary, it gives us more information.
Example. Say you see a chair in a well lit room. Now, say you turn down the light. It's true that when you see the chair at the two different times, it looks different each time. But that doesn't mean it is different, or that our perception is flawed. We see the object because our eyes work in conjunction with the environment around us. If the light is dimmer, the chair appears darker. But what do you expect? Those arguing against the senses seem to want a view of the chair that doesn't matter which direction you're looking at it from, what the light source is, or anything else.
In other words, they want a causeless perception of the world. They want to be connected to the world, but not by any means. This is the source of the Objectivist complaint that they damn our sight because we have eyes, or they damn our minds because we think.
Instead, the Objectivist view is a causal view of perception. We see because light waves bounce off the chair, hit our eyes, are converted into electrical signals to the brain, and get presented to our minds in some form. The Objectivist position is that this is an automatic process. The events happen causally from the input. Our mind doesn't get involve until it receives the signal.
And so we're presented with input from the world. We then have to process that input. For instance, if you look at a glass of water, you're seeing some translutcent object, with another translucent liquid inside. You do see it. But then your mind has to take over. The first thing you do is try to figure out what it is you're looking at. You identify the object as a glass of water. What you see is something, but what you recognize is a glass of water. That's where your mind takes over, and that's the point where you can start making mistakes. Perception is automatic and causal, and therefore reliable. Mistakes only happen when your brain starts doing some analysis, and that starts when you try to recognize the object as something you know.
So lets go back to the bent stick in the water. It appears to be bent, but that's not entirely accurate. Really, it just appears as something. Your mind evaluates it as being bent, since it looks kind of like that. But the conclusion is your own to make. The input is sent as is, and you are in charge of evaluating it. The fact that a child might think it's bent is because they haven't grasped, and integrated, how refraction modifies what they see.
Let's give another example. If you take a black and white picture of something, your senses aren't flawed by not providing you with the correct colors. You know your seeing it correctly. You adjust to the black and white by understanding how the causal connection to your brain works. And that's an important part of it all. Those people who don't recognize it as a causal chain of events won't try to see how different factors can change how you see something. They'll insist the perception is flawed, and so we can't count on our one link to reality.
One more example, which is related. Imagine you're color blind. So you only see things in black and white. Now, are your senses flawed? Are you seeing the world incorrectly? The answer is no. The causal chain is still there, although it works different for you. You are still connected to reality. You may not have easy access to some data, but that's not a flaw. That's how everything is. Because there's a means of gaining knowledge, it is necessarily limited. There's nothing wrong there. Just as real people don't have x-ray vision but they still view the world fine, a color blind person is fine too.
Another kind of argument against perception is the view that our senses create a picture for us, and then we view the picture. So if you look around you, it's like the room is a snapshot, and so you're viewing it indirectly. This would be considered another blow to perception because it means that you're not viewing the real world, only an image of it. And because it's just an image, you don't know how close to real it is. But the Objectivist position works against this too. Our senses don't create some kind of picture, like a snapshot, which we view. The senses are a causal link to the outside world. When light hits our eyes (or soundwaves hit our ears), it gets transmitted to our brains causally. There is no intermediate agent that creates a false image. We view it directly. That might be a little confusing, since it's a long chain of cause and effect. But the point is that it is a chain of cause and effect. The stimulus to our nerves lead automatically to a reaction in our brains, which is our perception. It doesn't get translated, as if there were some agent in between deciding what we see and what we don't see. It's just presented. Look at it from the view of how it can go wrong. If I drew a sketch of what I see and gave it to you, you'd have my version of things, which might not be accurate. But if you see it for yourself, you don't have the middleman who picks and chooses what you see. All of it gets to you, and since there's no selection process along the way, there's no room for mistakes. I hope that makes sense.
Another interesting problem is the difference between sensations and perceptions. Sensations are supposed to be vague results of our senses. For instance, you see a brownish color. Or you see a large whitish shape. Perceptions are integrated. Like you would see a glass, or a book cover, or a computer monitor, or something. Let's think art for a minute. To draw a glass of water, you could sketch the shape and essential qualities. But a real glass has light reflecting off of it, different shades of color, etc. Sensations, as far as sight goes, is just supposed to be a bunch of colors of various brightness.
So which do we actually see? Sensations or perceptions? If we just see sensations, then our minds are doing a whole lot of interpretive work on it afterwards. You'd have to guess that these blobs are part of these other blobs, and when taken as a whole resemble something like a glass of water. And that means more room for error. The perception school of thought is that we don't see blobs of color, really. We see entities. We see a glass of water (recognizing it as a glass of water is something else). So we see the shape of it, we see that there's different light patterns in it, we see there are dropplets of water on it, etc. We see it not as some blurry set of colors, but as an object. The explanation for this would be that the means of integrating the light is an automatic process of our brains. In other words, we're hard-wired to integrate some of the data. We see sharp linear contrasts of colors, and detect edges of an object. Our brains take the data from two eyes, and put them together to give us depth perception. Etc.
Why does this matter? Well, I bring it up because there are some arguments on this topic, so you should at least be familiar with it. But it's also related to the validity of the senses. Look at the world around you. You see objects, right? When you look at a flower, it's not a blob of colors which you untangle. You see it as a single object. The question is really how you get there from blobby colors. If it's automatic, life is good. If it's a product of your mind, and you're not aware of the process by which you do it, then it could be entirely wrong. Anytime you make judgments, you have the possibility of error. The argument would be something like "You see what you want to see. Sure your eyes transmit data to your brain, but then you just interpret the data any old way you want to. You're just fooling yourself."
The last thing I want to hit on is that when I talk about senses, you probably think sight, hearing, touch, and taste/smell. That's all true. You do gain information from the world that way. But you also experience your inner world directly. You feel emotions. You experience the process of thinking, of focusing, of wandering with your mind, etc. All of this is directly accessible to you. So all of this can provide you with information you need in order to gain knowledge. You can think of these as inner senses.
That's it on senses and perception. Feel free to ask questions as usual.