PHIL2606: Knowledge, Reason and Action
Week 8: Skepticism
We often are skeptical (i.e. doubt) that someone really does know what she claims to know.
My brother in law, for example, claims to know all sorts of things; I am skeptical that he really does. Most of us claim to know that astronauts landed on the moon; some people are skeptical that we really do.
We sometimes give reasons for our skepticism:
- Harry: Kahlefeldt came 11th in the triathlon.
- Skeptic: You don't know that, you're just making it up!
- Mary: I know that my car is parked on City Road.
- Skeptic: Really? Someone may have stolen it since you parked there.
We can think of the skeptic in each of these examples as (very succinctly) giving an argument that the person does not know:
- You just made it up that Kahlefeldt came 11th in the triathlon.
- If you just made it up that Kahlefeldt came 11th in the triathlon then you don't know that Kahlefeldt came 11th in the triathlon.
- Therefore, you don't know that Kahlefeldt came 11th in the triathlon.
- You don't know that no one has stolen your car and driven away.
- If you don't know that no one has stolen your car and driven away then you don't know that it is parked on City Road.
- Therefore, you don't know that your car is parked on City Road.
This second kind of argument is an interesting one. We can generalise it as follows. Suppose that someone, s, claims to know something, p. Suppose that q is a skeptical alternative to p; that is, a proposition such that (a) q is incompatible with p (i.e. they cannot both be true), and (b) s does not know not-q. Then we can argue that s does not know p, as follows:
- s does not know not-q
- If s does not know not-q then s does not know p
- Therefore, s does not know p
So if someone, s, claims to know something, p, then one way to argue that s does not know p is to come up with a skeptical alternative to p and argue as above.
(Here might be another way of expressing one's skepticism: ask, ‘How do you know’? Consider:
- Tom: Humans have been to the moon.
- Skeptic: How do you know?
- Mary: My car is parked on city road.
- Skeptic: How do you know?
What is going on these cases? Can we think of the skeptic as giving an argument?)
More worrying skepticism
The examples above are cases of everyday skepticism, and are not particularly worrying: no one cares too much if Harry doesn't know, and it is not uncommon to find out that you don't really know where your car is.
Also, Mary has a way of coming to know whether or not the skeptical alternative is true. Granted, she does not currently know that no one has stolen her car and driven it away, and so she might not know that her car is parked on City Road. But at least she has a way of checking whether or not anyone has stolen her car.
But here is a much more worrying case. You and I claim to know that we have hands. But consider this skeptical alternative: we are all BIVS - handless brains-in-a-vat, being stimulated by scientists to have the course of experiences that we do. Consider this argument:
The BIV argument
- You do not know that you are not a BIV.
- If you do not know that you are not a BIV then you do not know that you have hands.
- Therefore, you do not know that you have hands.
Why more worrying? Because:
That we have hands is a pretty common and uncontroversial thing to claim to know. After all, if we don't know that we have hands, then what do we know? Or, to put it slightly differently: if we know anything at all, then we know that we have hands!
We seem to have no way of checking whether or not this skeptical alternative is true: how would we go about checking to see whether or not we are BIVs? What kind of experiences would settle the matter? So the argument suggests not only that we do not know that we have hands, but that we cannot know.
We can think of the BIV argument as presenting us with a paradox: seemingly valid reasoning from seemingly true premises lead us to a seemingly false conclusion. What has gone wrong? Call this the BIV paradox.
The scope of the BIV argument
The conclusion of the BIV argument is that you do not know that you have hands. The same skeptical alternative (that you are a BIV) could be used to argue for the following conclusions as well:
- You do not know that you have feet
- You do not know that you go to university
- You do not know that you had dinner last night
In general, it could be used to argue that you do not know p, for any proposition p that is not compatible with the proposition that you are a BIV.
The BIV alternative cannot be used to argue that you do not know p, if p is any proposition that is compatible with the proposition that you are a BIV. So it cannot be used to argue for the following conclusions:
- You do not know that there are brains
- You do not know that there are vats
- You do not know that you are a brain in a vat
(Perhaps there is some other way to argue that you do not know these things.)
So the BIV argument has limited scope. It does not lead to global skepticism (i.e. skepticism about all claims to knowledge), but a more local skepticism. Still, the kind of skepticism that it leads to is a worrying one.
Here is another interesting skeptical alternative (due to Bertrand Russell): the universe came into existence only five minutes ago, complete with all its historical evidence, including our 'memories'. This does not lead to skepticism about our knowing that we have hands, but it does lead to skepticism about our having knowledge of the past (e.g. it can be used to argue that I do not know that I was born in Gunnedah). This is another kind of local skepticism.
Here is another skeptical alternative (made famous by Descartes): I am at home in bed dreaming right now. This does not lead to skepticism about my knowing that I have hands, or my knowing that I was born in Gunnedah, but about my knowing that I am giving this lecture - yet another kind of local skepticism.
Note that completely global skepticism about what we know is a difficult position to argue for. Suppose that we have the following norm of assertion: assert only things that you know. If there is nothing that we know, then we ought not assert anything. So we ought not assert, "No one knows anything", or "I believe that no one knows anything". This makes it very hard to argue!
Possible responses to the BIV argument
How might we react to the BIV argument? We have at least the following responses available to us:
- Accept the conclusion (that we do not know that we have hands)
- Reject the first premise (that we do not know that we are not BIVs)
- Reject the second premise (that if we do not know that we are not BIVs then we do not know that we have hands)
- Deny that the argument is valid
Accepting the conclusion
One fairly natural first response is to just accept the conclusion of the BIV argument: "Ok, so I don't know that I have hands."
But while it might be easy to say that you accept the conclusion, it is a very difficult position to consistently maintain.
If we don't know that we have hands, then there is a whole bunch of other stuff that we don't know either, perhaps nearly everything that we ordinarily claim to know. So to be consistent we would have to stop claiming to know all these things, should demand our money back from the university for failing to deliver us any knowledge, should own up to deserving 0% on all exams, and so on.
I doubt that anyone actually does this, even if they claim to accept the conclusion of the BIV argument. This suggests that they don't actually accept it (actions speak louder than words).
Observe: it seems that believing is not something that we can just decide to do. Suppose someone offered you a million dollars to believe that the moon is made of cheese; could you do it?
Suppose you claim to accept that you don't know anything, and probably cannot know anything, but continue to talk and act as if you do and can. For us to accept that you really have embraced ignorance, it would help if you could explain why you continue to talk and act as if you haven't. How might such an explanation go?
Rejecting the first premise: Moore
G. E. Moore famously rejected the first premise of the BIV argument by turning the argument around (see his Philosophical Papers (1959; London: Allen and Unwin), p. 247):
- I know that I have hands
- If I don't know that I am not a BIV then I don't know that I have hands
- Therefore, I know that I am not a BIV
We can put the second premise in its contrapositive form to make the validity of this argument clearer:
- I know that I have hands
- If I know that I have hands then I know that I am not a BIV
- Therefore, I know that I am not a BIV
We might say that Moore has modus tollensed the skeptic's modus ponens.
But it is hard to be satisfied by this response. Why?
It's not that Moore's argument is any less valid. If the BIV argument is valid then Moore's argument is too. In general, if the first argument below is valid, then the second is too:
- not-q; if not-q then not-p; therefore not-p
- p; if p then q; therefore q
It is sometimes said that Moore's argument begs the question against the skeptic (and here I don't mean raises the question). The skeptic doubts that we know that we have hands (and is presenting an argument that we don't). So when Moore uses as a premise the claim that we do know that we have hands, the skeptic is not going to accept Moore's premises, and will not find his argument persuasive.
But, by the same token, doesn't the BIV argument beg the question against Moore? Moore doubts that we do not know that we are not BIVs (and is presenting an argument that we do). So when the skeptic uses as a premise the claim that we do not know that we are not BIVs, Moore is not going to accept the skeptic's premises, and will not find her argument persuasive.
I suggest the problem with Moore's response is this. What the BIV argument does is make us realize that three things we find very plausible are inconsistent (i.e. cannot all be true):
- We do not know that we are not BIVs
- If we do not know that we are not BIVs then we do not know that we have hands
- We know that we have hands
Moore seems to think that it is clear what must be given up: the first claim, that we do not know that we are not BIVs. He might be right that this is what must be given up, but to the rest of us this is not at all clear. If we shared Moore's feeling about this then we would find his argument persuasive; but we don't, so we don't.
We find neither of the two arguments persuasive - the skeptic's or Moore's.
Contrast these with the following pair of arguments:
Evil exists; if evil exists then God does not exist; so God does not exist.
God exists; if God exists then Evil does not exist; so evil does not exist.
The first is a version of the classic problem of evil. The second is a 'Moorean' response to it. In this case the Moorean response seems much less plausible to many. Why? Not because it is any more question begging than in the BIV case. The arguments trade on the fact that the following three propositions cannot all be true:
- God exists
- If God exists then evil does not exist
- Evil exists
In this case it is clearer to many what has to go: the claim that God exists. That is why they are not persuaded by the Moorean response that appeals to the claim that God exists.
Perhaps this is a more persuasive way to argue against the first premise:
- I know that BIV technology does not exist
- If I know that BIV technology does not exist then I know that I am not a BIV
- Therfore, I know that I am not a BIV
- SEP: ‘Skepticism’, ‘Knowledge and Skepticism’ (supplement to ‘The Analysis of Knowledge’).
- IEP: ‘Contemporary Skepticism’.
- DeRose, K. and Warfield, T. (eds.) (1999), Skepticism: A Contemporary Reader (Oxford: OUP), Introduction.
Read Cargile, J. (1972), 'In Reply to a Defense of Skepticism', Philosophical Review, pp. 229-36. What is the view that Cargile is criticising? What is his main criticism?