牛津大学开放课程：哲学概论PPT讲义四

Lecture 4:

Two Cartesian Topics

Last Time …

This Lecture …

claims about the nature of MIND AND BODY. The Next Lecture …

will say more about modern responses to SCEPTICISM, and focus on KNOWLEDGE.

Vertical Scepticism

Horizontal Scepticism

as one has sensations or appearances, to expect similar sensations or appearances in the future).

It can seem that (“vertical”) external world

Maybe a wicked scientist has my brain in a vat, and is creating these illusions.

The only way to defeat scepticism is to When I consider “I think, therefore I am”, it

By contemplating this first certainty, I understand what makes it certain is that I clearly and distinctly perceive it to be true.

Hence I can establish as a general rule I clearly and distinctly perceive that God

A perfect God cannot deceive, so I know that my faculties are essentially reliable.

Descartes seems to be “boot-strapping”:

Isn’t this viciously circular?

If my faculties might be defective, then how

can I trust my proof of the existence of God in the first place? How can any anti-sceptical

argument even get off the ground?

G.E. Moore famously claimed to refute this

Modus Ponens

P is true P

therefore Q is true

Modus Tollens

Q is false¬Q therefore P is false¬P

The religious fundamentalist might say: Everything in the Bible is true.

The humane philosopher would say:

Genocide is never desirable.

Therefore not everything in the Bible is true. Which underlined premise is more plausible?

Moore says:

We know this is a hand .The sceptic says:

We don ’t know that there is an external world .

t know that this is a hand.Moore will claim that his premise is more

We’d like to agree with Moore, but it seems

But “internalist” arguments, like Cartesian

So many recent philosophers have moved towards externalism (next lecture, and

s approach to induction).

The view for which Descartes

immaterial substance This substance dualism is to be contrasted

(i.e. there are both physical and non-physical properties).

In his Discourse, Descartes argues like this: Compare:

I cannot doubt that Phosphorus is Phosphorus.

Hesperus = the Evening Star; Phosphorus = the Morning

both are appearances of the planet Venus.

If a and b are the same thing, then any

being doubted by me to exist me my body

being

doubted by me to be Prime Minister

To simplest way to avoid the fallacy is to deny that these are genuine properties.