Hannah asked:

Compare and contrast the contribution of Descartes and Hume to our understanding of the nature of
the external world.

============

Here are a few pointers. It's important to understand these philosophers if you are going to
understand the significance of skepticism. Descartes and Hume's arguments encourage one to take
the problems of skepticism very seriously. It seems to me that this is where their contribution to
understanding the nature of the external world lies.

I want to distinguish two kinds of skepticism for you to think about:

*
A skepticism that says knowledge about the external world is very hard to find.

*
A skepticism that says knowledge about the external world is impossible.

I'll talk a little bit about each philosopher's arguments, and I then want you to think about which kind of
skepticism applies to each philosopher. I hope this will help you compare and contrast their positions.

Descartes argues throughout his Meditationsthat we can't find out much about the external world via
the senses alone because the senses can be mistaken. Imagine you're walking through a field, he
says, and you see a square tower on the horizon. As you get closer however, you realise that you
were tricked by your position, and the tower is actually round. So you're senses cannot provide you
with certainties about the external world to the same degree that your reason can provide you with
certainties about geometry and the existence of yourself. Descartes model of certainty, of course, is
the claim that its impossible to doubt that you exist because doubting equals thinking and thinking
means you must exist for that to be so.

Then Descartes does something else however. He asks us to consider whether a malicious demon is
deceiving us into thinking that the truths of reason are universally true. Would we know if he were?
Even if we cannot conceive of ourselves thinking but not existing because that seems to make no
sense, perhaps it is possible because the laws of reason are not as we think them to be. So perhaps
even reason cannot yield truths about our world. At this stage, Descartes attempts to prove the
existence of God in order to show that God would not do that sort of thing to his creation because
God is good. So our reason isable to find truths about the world because we know that God wouldn't
ever deceive us. Some philosophers have thought this argument viciously circular because Descartes
uses a rational argument for God to validate the authority of reason.

Roughly, Hume thinks that all knowledge comes from sensory experience however. He argues in a
variety of ways that sensory experience is not sufficient to ground our beliefs in the existence of
causation, matter and what he calls 'continued and distinct existences'. On the basis of what we
perceive, for example, we never see one thing cause something else. We just see events constantly
followed by other events, and have to infer that the prior event causes the later one. He thinks that on
the basis of what we perceive, we are not entitled to make that inference, however lazily we slip back
into our familiar patterns of thinking later. So neither the senses nor reason can allow us to discover
certainties about the external world according to Hume. Likewise with matter, the only thing we see
and touch are the qualities of objects, not the property-less stuffof which they are supposed to be
made. So why think that matter and causation are features of the universe when you can never see
or know them?

Descartes and Hume both raise troubling skeptical issues. Hume takes skepticism about the ability of
our senses to discover certainties to its logical conclusion, while Descartes' skepticism about the
malicious demon casts doubt even on the power of our reason to find out about our world. It might be
helpful for you to pursue your comparison by relating the two kinds of skepticism I mentioned to the
arguments that these philosophers raise.

Adam Gatward