The skeptical argument based on the premise that knowledge requires evidential certainty

Question 1

Skepticism about the external world

Answer 1

• Considered to be the totality of physical things, our bodies included, that strike us being ‘out there’, beyond our minds
  ○ Ex. cats, the planet, your body
• “Propositions about the external world” are propositions about any of these things
  ○ Most arguments for skepticism involve the presentation of skeptical hypotheses
• Any hypothesis one cannot rule out that would make false most of one’s external world beliefs if it obtained

Question 2

Skeptical hypotheses

Answer 2

René Descartes:
- The dreaming hypothesis
○ You are asleep and dreaming the ‘real life’ you think you are living
- The evil demon hypothesis
○ You are a bodiless ego in a void. The only thing in existence is a ‘malicious demon of the utmost power and cunning’ who has been supplying you with a sequence of vivid hallucinations of the ‘real life’ you thing you are living
One from the Matrix series:
- The brain-in-a-vat hypothesis
○ You are bodiless BIV kept alive in a nutrient bath and supplied with a sequence of vivid hallucinations of the ‘real life’ you thing you are living

Question 3

“Certainty”

Answer 3

• Psychological certainty
  One is psychologically certain of proposition P if one has no doubts whatsoever regarding P
• Evidential certainty
  One is evidentially certain of proposition P if one’s evidence for P “guarantees” P, that is, if one’s evidence is logically incompatible with not-P

Question 4

Descartes’ argument for skepticism

Answer 4

• (P1) Our evidence for the external world propositions we believe does not guarantee that any of them is true.
• (C1) We are not evidentially certain of any propositions about the external world. [P1 and definition of “evidential certainty”]
• (P2) Knowledge requires evidential certainty: For any proposition about the external world P, one knows P only if one is evidentially certain of P.
• (C2) We do not know any propositions about the external world. [C1 and P2]

Question 5

Ways to resist Descartes’ argument for skeptcisim

Answer 5

• Perhaps P2 is too strong; maybe knowledge isn’t linked to certainty in the way Descartes seems to assume
• But, maybe there is a conversational rule that says: don’t assert a knowledge claim unless you feel certain”
• If so, we can deny P
• Therefore, we cannot rule out skeptical hypotheses like the evil demon hypothesis. But that just shows P1 is true. Given that knowledge required evidential certainty, we don’t and cannot know anything about the external world
• Descartes does not endorse this argument and believes it is unsound. But he considered it because he believes it is a powerful threat to the commonsense view that we have knowledge of the external world.

Question 6

Skeptic’s response to Moore

Answer 6

• What if the skeptic were to insist that the proof fails because Moore has failed to prove his premises
  Moore: it may be impossible to prove them but it doesn’t matter; we can know things that we cannot prove

Question 6

Moore’s proof of an external world

Answer 6

• (P1) Here is a hand. (Said while gesturing with one’s right hand.)
• (P2) Here is another hand. (Said while gesturing with one’s left hand)
• (C1) Two human hands now exist. [From P1 and P2]
• (P3) If two human hands now exist, then there are external objects.
• (C2) There are external objects. [From C1 and P3]

Question 7

Moore’s “commonsense” methodology

Answer 7

• Insists that if the skeptic tries to assert otherwise then the skeptic will need an argument
• But Moore says any argument like this will counter to our everyday sense that we really can know that we have hands
• His point is that in a conflict between a contentious bit of theory and our sense that we know we have hands, we should side with common sense
• His chief point is really methodological. He feels we should trust our intuitive sense that we do know we aren’t always hallucinating before we trust doubtful (any premise the skeptic uses in his argument will be a piece of doubtful philosophy)

Question 8

Moore’s way of resisting the skeptical argument

Answer 8

• He challenges P1
• If pressed to defend P1, the skeptic would say it is possible for one to have the same sensory evidence that one would have if there is an external world even if there isn’t an external world (i.e. in the evil demon skeptical)
  But, he asks, where is the argument for this, can it be proven

Question 9

Problems to Moore’s approach

Answer 9

1. Request for clarification
   a. Consider: I am wide aware. If I am wide awake, then I am not dreaming. I am not dreaming
   Moore says he cannot prove that is not now dreaming, but doesn’t this little argument meet his standards for proof

Question 10

Vogel’s take

Answer 10

Thinks this line of reasoning amounts to an even more challenging case for external world skepticism than the original argument we were trying to resist

Question 11

The “underdetermination principle”

Answer 11

If you are faced with 2+ mutually exclusive hypotheses, and the information available to you gives you no reason to believe one rather than the other, then you don’t know that either hypothesis is the case

Question 12

Vogel against premise

Answer 12

• He considers and rejects some interesting ways of denying premise
• Moorean “dogmatism”
  ○ In virtue of the phenomenal character of your visual experience as of a tomato you are justified in believing that there is a tomato; since there being a tomato would entail your not being deceived, you are justified in believing that you are not deceived
• “A priorism”
  ○ We have a priori grounds (reasons not stemming from sensory experience) for trusting that we aren’t deceived
• “Explanationism”
  Despite his misgivings concerning dogmatism and a priorism, Vogel thinks that premise * is false. His view is that we do have reason to believe that our sensory experiences are caused by a real world (and that we are not deceived).