I’ve spent a lot of energy dealing with this skeptical argument, that I’ve called “The Argument from Ignorance” (AI):
1. I don’t know that I’m not a BIV
2. If I don’t know that I’m not a BIV, then I don’t know that I have hands
So, C. I don’t know that I have hands.
I’ve always thought it a very promising object of study, because it’s valid, both its premises are intuitively very plausible, yet its conclusion is highly implausible (for some, it borders on the absurd). So you’re bound to find out something at least somewhat surprising, and perhaps even important, about knowledge in solving the puzzle this argument presents us with.
But in recent years, I’ve noticed something of a trend among philosophers – usually in conversation, but sometimes in print – to think this isn’t a very strong skeptical argument, perhaps not even worth working on. (Often they have some other argument skeptical argument they’re advocating as the “real” skeptical threat. Invariably, I think end up finding this “real” threat to be far less threatening.) Mostly, they’re worried about the argument’s first premise.
Now, I believe they have correctly fingered the argument’s weakest think. But I think it’s pretty strong for a weak link. (The reason I find the alternative threats less threatening is that I invariably find them to include some premise far less plausible than 1, above.)
Often, a key point in the discussion over the power of this argument is the matter of how intuitively plausible that first premise is. (One might also wonder whether our not being BIVs falls into some broader pattern of things that we intuitively seem not to know. I think premise 1 scores pretty highly here, but that’s a long story.)
I have a report from “the front” on the intuitive plausibility of 1. For three years now, I’ve started off my introductory Descartes-to-Kant survey course, a large course which mostly draws students with no previous philosophy classes, with the question of whether the students know that they’re not BIVs.
This is the very first thing I do in the whole semester. (I justify (rationalize?) the exercise by relating it to my lecture on Descartes’s First Meditation later in the opening meeting.) So I’m mostly receiving the verdicts of people “unspoiled by philosophy” – or at least by their contact with philosophy classes.
Here’s how I take my poll. The opening item on the lecture outline is: “A Philosophical Question or Two.” (“Or Two” because, depending on how I’m doing for time, I might also ask whether they think it’s possible that they are BIVs, which can later facilitate discussion of the second great argument by skeptical hypothesis, like unto the first, the “Argument from Possibility.”) I write these options on the board: “I know that I’m not a BIV” and “I don’t know that I’m not a BIV.” I prepare by explaining the BIV hypothesis, but refraining from using terms of epistemic appraisal in my description of the hypothesis. (So, for instance, I’m very careful not to say anything even remotely like, “So, if you are such a BIV, you can’t tell that you are,” since I take “can’t tell” to be a question-begging negative assessment, or at least to be question-beggingly close to being a negative assessment, of any belief one might have to the effect that one is not a BIV.) I then tell them that I’m going to take a show of hands on the question of whether each student thinks she does, or does not, know that she’s not a BIV. The first time I did this, I noticed a lot of glancing about by the students as I waited for the first show of hands. This made me worry that many were being influenced by how others voted. So the last two times I did this, I explained to them that I would wait quietly a few seconds to let everyone make a firm decision in their own minds as to what they thought, so they wouldn’t be influenced by how others were voting when I did ask for a show of hands.
The results were extremely strong. The first time I did it, I got these results (as reported in note 15 of my paper “Sosa, Safety, Sensitivity, and Skeptical Hypotheses,” forthcoming in SOSA AND HIS CRITICS, but on-line in draft form here [word format] and here [pdf format]):
I recently took a poll in a class of over 70 introductory philosophy students….My question was whether or not each student, in her or his own opinion, knew that she or he was not a BIV. A clear majority — about 2/3 of the class, it seemed, though I didn’t count — of the hands went up. So most of these students agreed with the skeptic on this issue. When I asked who thought they did know they weren’t BIVs, only three hands went up.
The last two times, the results were even stronger. I suspect it’s really about as strong as you can hope for from undergraduate classes on just about any question – including whether killing babies for the fun of it is morally wrong. Well over 80% voted that they didn’t know, and in each case, less than 5 (in classes of about 100 students, which is what this course has drawn for the last two years, at least for its opening meeting during Yale’s “shopping period” – before I frighten some off with such questions!) voted that they did know. (So there were still some abstainers. It’s possible that there were fewer abstainers the last two times because of my instructions to firmly make up their own minds before I took the show of hands.)
Perhaps others have obtained different results. I’d then be interested in some details about how the opinions were collected. One very important feature of how I do things is that I do not present any skeptical arguments until after I’ve taken the vote. Explaining and then asking the question of whether they know they’re not BIVs is really the first thing done in the course. If students are presented with the question in a format where it’s clear that a negative verdict on whether they know they’re not BIVs forms an important part of an argument designed to show that they don’t even know they have hands, many might decide that they do know that they’re not BIVs in order to escape the threat the argument poses. (Of course, some may worry about such skeptical threats on their own, without having to be presented with the argument.)
All of this can lead one to think that AI really is a remarkable argument. Any argument whose weakest link is that intuitively powerful and yet has such an implausible conclusion is something of a wonder.