1. Accounting for the Data and Skeptical Hypotheses

There's a certain way that things seem to you now. For example, it may seem to you as if you are reading these words on a webpage, that the computer screen you are staring at is glowing a certain bluish-purplish color, that the computer is humming and making certain electronic sounds, and that you're a bit peckish and could use a slice or two of cheese. There are numerous ways things might seem to you right now, including how things apparently look and feel and smell and taste and sound, etc. However, there are also numerous ways that things do NOT seem to you. For example, it probably doesn't seem to you right now as if you are climbing Mt. Fuji, or skydiving out of an airplane, or eating overcooked, giant squid. In what follows, we just want to concentrate on the way things seem to you now, which we will call the data. 

Any plausible hypothesis about the world is has to (at the very least!) account for the data. It will have to explain why it is that we have the data we do, or why it is that things seem to us the way that they do. Notice that every skeptical hypothesis that we discussed in class (2/15/06), was specifically tailored to account for the data. Below are some examples of the hypotheses we considered:

    Descartes' Evil Demon Hypothesis: The reason that things seem to you now the way that they do is because there is an evil demon deceiving you and manipulating your mind at every second. He is making you think about certain shapes and colors and sights and sounds, even though all of it is an elaborate trick, and none of your sensations are veridical. So, according to this hypothesis, even though it may seem to you now that you are reading typed words on a computer screen, you are really just being fed these sensations by an Evil Demon, who doesn't want you to know what the world is really like.

    Matrix Hypothesis: The reason that things seem to you now the way that they do is because there is gigantic super-computer that has taken over the world. The computer is now using human beings as batteries to keep itself going. Yet in order to pacify us human beings as we are being gutted for energy, we are fed an elaborate computer program that makes us think the world is a certain way. So you may think that you are reading typed words on a computer screen, but this is     just an illusion produced by the elaborate computer program.

    Brain-in-a-Vat (B.I.V.) Hypothesis: The reason that things seem to you now as they do is because you are really just a lumpy, somewhat soggy, gray mass of a brain, floating in a vat of fluid, hooked up to a computer through cables and wires and fed false information about what things are like. You may think that you have a body and hands and eyes through which you are reading these very words, but really you are just being fed the sensation of seeing and feeling directly to your neurotransmitters via some complicated circuitry.

    Painted Horses Hypothesis: Everything is pretty much the way you think it is, except for any 'zebras' that you might have seen, or thought you saw. This is because there is a madman on the loose who is trying to fool the biologists and everyone else into thinking that there is this exotic animal called a 'zebra.' In reality, however, this madman is actually going around and painting selected horses with black and white stripes, retouching old photos and paintings of such animals, and producing fake documents to make all past studies of 'zebras' seem real. The reason it may seem to you as if there are zebras is because the madman has been very good at his elaborate hoax.

    Desk-Hologram Machine Hypothesis: Everything is pretty much the way it seem to you now, except for the one desk in front of the classroom where we meet for class. This is no desk; it is merely a really good hologram of a desk. The hologram machine is cleverly hidden behind the podium at the front of the room.

    My Cat is an Alien Hypothesis: Everything is pretty much the way it seems to you now except that my cat is an alien from a highly evolved and sophisticated outer-space race. The reason she sleeps so much is because she is intellectually under-stimulated here, and has melted her brain away by watching too much TV with me. The reason she's so fat is a bit of a cosmic mystery.
   
    Everything is Pretty Much the Way it Seems Hypothesis: The reason things seem to you now the way they do is because things are actually the way they seem to be. Why does it seem to you as if you're reading typed words on a computer screen? Because you ARE reading typed words on a computer screen. Duh.

Again, each one of these hypotheses accounts for the data. So the question now, of course, is: on what grounds do we pick one hypothesis over another? Since each one accounts for the data, what resources do we have to say that one of the hypotheses (e.g., the last one) is true while the others are false?

Skepticism is the view that we have no way of justifiably choosing one hypothesis over another. And, so, when it comes to what sorts of things we can know, the skeptic's response is: not much. For in each hypothesis above, the sorts of things we can know or be sure of changes. And if we can't be sure which hypothesis is right, then we can't be sure which things we can know, and which things we can't.

A quick note on Descartes: if Descartes' cogito is right (see the Descartes page here for a quick summary), he would essentially be saying that the one thing you can be sure of--no matter which of the above hypotheses is correct--is that you exist. Since each of the hypotheses is designed to account for the data, and part of the data is that you are thinking, or doubting, then the one thing you can be certain of is that you exist. So, no matter which hypothesis is right, the one thing you can be sure of is that you exist.

2. Global and Local Hypotheses

Notice that the above hypotheses vary from in their skeptical severity. Descartes' Evil Demon Hypothesis, for example, gets you to doubt that you know most of what you think you know. You might have thought that you have hands and are sitting in front of a computer right now, counting the seconds until happy hour, but really, all of these sensations are produced by an evil demon who is only making you think that these things are true. This hypothesis makes you doubt nearly all of your beliefs, such that you are not even sure whether 2+2=4 or a triangle has three sides. The Desk-Hologram Machine Hypothesis, on the other hand, gets you to doubt only a small number of your beliefs--namely, whether the desk in the front of the classroom where we meet for class really is a desk or not. Other of your beliefs, such as whether or not you have hands or whether or not you are staring at a computer screen right now, are unaffected by this hypothesis. Let's call hypotheses that rob us of most (if not all) of our apparent knowledge global skeptical hypotheses, and let us call hypotheses that rob us little to none of our apparent knowledge local skeptical hypotheses. Hypotheses about what the world is like and how we can come to know it can then be seen to range on a spectrum of more global hypotheses on one end, to more local hypotheses on the other. The Matrix Hypothesis, for example, is more global, whereas the My Cat is an Alien Hypothesis is more local. In this way, we can judge the severity of a skeptical hypothesis depending on how much of our apparent knowledge is robbed from us when we suppose the relevant hypothesis is true.


3. Closure and Skepticism

Closure is a fairly intuitive principle about knowledge that runs roughly as follows:

If you know some proposition, p, and you know that p entails some other proposition, q, then you are in a position to know that q.

For example: suppose that you know that you're at Woody's. You also know that if you're at Woody's, then you know that you're not a brain in a vat made to merely think you're at Woody's. So, you know that you're not a brain in a vat made to merely think you're at Woody's. You probably already knew that you weren't a brain in a vat--at least, you probably knew that before coming to philosophy class this week--but that's not the point. The point is that you can extend your knowledge by considering what is logically entailed by the things you already know. This is closure.

This principle, while initially intuitive, has some problems. If Descartes' Evil Demon Hypothesis is right, for example, then we can't know a bunch of things that were seemingly entailed by things we thought we knew. For instance, you know that if you're at Woody's, you are not a brain in a vat made to merely think you're at Woody's. You might have thought that you were at Woody's, thus entailing that you are not a brain in a vat made to merely think you're at Woody's. But how could you possibly know that? If you were a brain in a vat made to merely think you're at Woody's, you wouldn't be able to tell whether you were actually at Woody's or not (because if you were a brain in a vat, all of the data would be accounted for, just as it would if you actually were at Woody's). So, since you can't know that you're not a brain in a vat merely made to think you're at Woody's, you can't know that you're at Woody's.

The idea here is that you might have thought that you knew that you weren't being deceived by an evil demon, but since you can't know whether you are or are not being deceived (i mean, think about it: how could you know, if the deception is good enough?), then you can't know most of what you thought you knew. So, closure, if accepted, can be used not only to extend our knowledge, but also to take it away. If we can't know that we're not being deceived, then we can't know anything that entails that we do know that we are not being deceived.

---

Back to Meg's Phil 26 (Spring 06) Page
Back to Meg's Teaching Page
Back to Meg's Main Page