## Wednesday, September 7, 2016

### Solving Descartes's Problem

Announcements
• Week 2 homework grades and comments will be in Canvas this afternoon.
• We'll discuss homework expectations on Friday.

Descartes's Problem

Truman's Problem

Solution #1 -- No Solution

Skepticism about knowledge of the external world.  Descartes can't know there's a fire. He can't know anything about matters outside of his own mind.

Solution #2 -- Doing Experiments

Truman's reasoning:
(1) Either my world is natural or it's fabricated by strange forces
(2) If it were natural, and I did X (e.g. drove in an atypical direction), then I would observe Y (e.g. the usual cars).
(3) But when I do X (e.g. drive in an atypical direction), I don't observe Y (e.g. the usual cars).
So (4) My world is fabricated by strange forces.
What experiment could Descartes do to prove that either there is or isn't an evil deceiver?  If this sort of solution could work for Truman, could it work for Descartes?

Could Descartes experiment and reason in a similar way?
(1) Either the fire image in my mind is caused by a real fire or it's caused by an evil deceiver.
(2) If if were caused by an evil deceiver and I did X, I would observe Y.
(3) But when I do X, I don't observe Y.
So (4) The fire image in my mind is caused by a real fire.

GROUPS:  SEE IF YOU CAN COME UP WITH X AND Y FOR DESCARTES.

Solution #3: Jonathan Vogel's "Explanationist" Solution

The Deceiver Argument.  (This is the argument that disturbs Descartes in Meditation I.  The skeptic thinks it's a sound argument.)

Vogel says The Deceiver Argument is unsound.  Why is it unsound?  Because (he says) premise (2) is false.  He talks about a couple of other accounts of why it's false and then presents Explanationism as his own reason.

Explanationism. Descartes has two competing hypotheses to explain his mental image of the fire, but Vogel says they are not equal.  One is a better hypothesis than the other. So Descartes has reason to choose the better of the two. This is known as "inference to the best explanation" and we use this sort of reasoning all the time. If Vogel is right here, then premise (2) of the Deceiver Argument is false.

Vogel uses the examples below to convince us that there are better and worse hypotheses:

Ex. 1.  Dr. G sees his patient Roger and has two hypotheses about what's causing his symptoms.
1. allergy hypothesis (better because generalizes to other cases)
2. something else hypothesis (worse because ad hoc)

Ex. 2.  Two people are debating why you reach the same location, if you keep traveling in the same direction
1. round earth hypothesis (better because simple)
2. flat earth hypothesis--you'll be drugged and abducted by aliens to get from one edge to the opposite edge (worse because needlessly complicated)

Back to Descartes! Why is the fire dying down?   Descartes will struggle between two hypotheses--

1. real world hypothesis--log is being consumed (Vogel says: better because simpler)
2. evil deceiver hypothesis--ED is generating a sequence of flame images, each smaller than the previous one (Vogel says: worse because needlessly complicated)

Since the real world hypothesis is superior, premise (2) of the Deceiver Argument is false.

Solution #4: Descartes's Very Own Solution

Solution #5: Reliabilist Approach