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\title {Descartes \\ Lecture 03}
 
\maketitle
 

Lecture 03:

Descartes

\def \ititle {Lecture 03}
\def \isubtitle {Descartes}
\begin{center}
{\Large
\textbf{\ititle}: \isubtitle
}
 
\iemail %
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why?

Doubt is necessary to establish ‘anything at all in the sciences that is stable and likely to last’

Aim for this lecture is to understand why Descartes might say this.
Let’s start with an easier question ... maybe if we understand what reasons Descartes provides for doubt, we will understand better why doubt is necessary.

Meditations (Synopsis)

Reasons are provided ‘which give us possible grounds for doubt about all things, especially material things,
so long as we have no foundation for the sciences other than those we have had up until now’

What are these reasons?

Argument ideas from Meditation 1

The senses sometimes deceive us

My brain may be ‘damaged by the persistent vapours of melancholia’

The dream argument

The deceiving God hypothesis

Cosmic deception

bad things might happen

How can the mere possibility that they might obtain give us grounds for doubt?

Argument ideas from Meditation 1

The senses sometimes deceive us

My brain may be ‘damaged by the persistent vapours of melancholia’

The dream argument

The deceiving God hypothesis

Cosmic deception

 
\section{Cosmic Doubt}
 
\section{Cosmic Doubt}

‘How do I know that he has not brought it about that there is no earth, no sky, no extended thing, no shape, no size, no place, while at the same time ensuring that all these things appear to me to exist just as they do now?’

Meditation 1

Terminology:
you are cosmically deceived exactly if he has done this.

\subsection{Cosmic deception} ‘How do I know that he has not brought it about that there is no earth, no sky, no extended thing, no shape, no size, no place, while at the same time ensuring that all these things appear to me to exist just as they do now? What is more, since I sometimes believe that others go astray in cases where they think they have the most perfect knowledge, may I not similarly go wrong every time I add two and three or count the sides of a square, or in some even simpler matter, if that is imaginable?’
Is this a reason to doubt all things?

Sensory perception plus knowledge of platitudes alone do not enable you to know that
this planet is round, not flat.your birthplace has not been struck by a meteor.the world outside this room continues to exist.you aren’t cosmically deceived.

The senses are concerned with the appearances of things here and now.

You do know this platitude:
if you are drinking coffee, then you are not cosmically deceived

Suppose sensory perception alone enables you to know you are drinking coffee.

Then you would be in a position to know you are not cosmically deceived on the basis of sensory perception plus knowledge of platitudes only.

Therefore sensory perception alone does not enable you to know you are drinking coffee.

Look where we got from and to!
Note the limits of the argument. It is not a general scepitcal argument.
Are the premises of this argument true? Is it valid?

Meditations (Synopsis)

Reasons are provided ‘which give us possible grounds for doubt about all things, especially material things,
so long as we have no foundation for the sciences other than those we have had up until now’

Earlier I asked, what are those reasons? Now we know.
Note the qualification!

✓

Earlier I asked, How can the mere possibility that cosmic deception might occur give us grounds for doubt? Now we know.

How can the mere possibility cosmic deception might occur give us grounds for doubt?

This question is answered by the argument. The argument shows that we lack of knowledge of mundane things on the basis of sensory perception and knowledge of platitudes alone.

so long as we have no foundation for the sciences other than those we have had up until now

These are the questions I’ve been thinking about. I’ve given you my answers. You can find other answers by reading Descartes and the secondary literature. What will your answers be?

Questions

1. Is Descartes’ appeal to cosmic deception supposed to provide reasons which give us possible grounds for doubt about all things?

2. If so, how is Descartes’ appeal to cosmic deception supposed to provide reasons which give us possible grounds for doubt about all things?

3. Does it succeed?

\begin{enumerate} \item Is Descartes’ appeal to cosmic deception supposed to provide reasons which give us possible grounds for doubt about all things ? \item If so, how is Descartes’ appeal to cosmic deception supposed to provide reasons which give us possible grounds for doubt about all things? \item Does it succeed? \end{enumerate}
Steve’s attempt to answer question 2: \begin{enumerate} \item Sensory perception plus knowledge of platitudes alone do not enable you to know that you aren’t cosmically deceived. \item You do know this platitude: if you are drinking coffee, then you are not cosmically deceived \item Suppose (for a contradiction) that sensory perception alone enables you to know you are drinking coffee. \item Then you would be in a position to know you are not cosmically deceived on the basis of sensory perception plus knowledge of platitudes only. \item Therefore sensory perception alonedoes not enable you to know you are drinking coffee. \end{enumerate}

Argument ideas from Meditation 1

The senses sometimes deceive us

My brain may be ‘damaged by the persistent vapours of melancholia’

The dream argument

The deceiving God hypothesis

Cosmic deception

We’ve been considering just one argument idea.
Lots of arguments. Can ask the same three questions about each.

why?

Doubt is necessary to establish ‘anything at all in the sciences that is stable and likely to last’

This was my question at the start of the lecture. Note that Descartes isn’t claiming to be original ...

‘I had seen many ancient writings by the Academics and Sceptics on this subject, and was reluctant to reheat and serve this precooked material’

Second Replies

\citep[p.~94, AT VII:130]{descartes:1985_csm2}
In thinking about Descartes’ arguments in the first Meditation, it is important to remember what he is using doubt for. He does not want to establish that sensory perceptions actually deceive us. He only wants to show that they cannot be relied on to provide information about the essential nature of bodies.
Recall from our discussion of The World

‘I have not brought up these examples to make you believe categorically that the light in the objects is something different from what it is in our eyes

I merely wanted you to suspect that there might be a difference’

Descartes, The World (AT IX:6)

Compare Descartes’ strategy in The Meditations:

The usefulness of extensive doubt ‘lies in freeing us from our preconceived opinions, and providing the easiest route by which the mind may be led away from the senses.’

Meditations (Synopsis)

Recall our guiding question and the structure of the argument we are considering so far ...

?

How can we acquire knowledge about the essential nature of the bodies located outside us?

Sensory perceptions provide only very obscure information about the essential nature of bodies.

∴ Not by treating sensory perceptions as a basis for judgements about the essential nature of bodies.

How does this bear on our ultimate aim?
Perhaps this is a key idea ...

obscure -> does not enable you to know you aren’t cosmically deceived

not obscure (clear?) -> does enable you to know you aren’t cosmically deceived

For all your sensory perceptions reveal, you are not in a position to know that you aren’t cosmically deceived

Therefore, sensory perceptions provide only very obscure information about the essential nature of bodies.

How close do you think this is to Descartes’ argument in Meditation 1? Can you do better
Recall our guiding question and the structure of the argument we are considering so far ...

✓

?

How can we acquire knowledge about the essential nature of the bodies located outside us?

Sensory perceptions provide only very obscure information about the essential nature of bodies.

∴ Not by treating sensory perceptions as a basis for judgements about the essential nature of bodies.

why?

Doubt is necessary to establish ‘anything at all in the sciences that is stable and likely to last’

Two Interpretations

1. The sciences need a metaphysical foundation.

2. This foundation must include a refutation of scepticism.

1. The assumption that sensory perception enables us to know the essential nature of things leads to bad science.

2. Reflection on possible grounds for doubt provides reasons to reject this assumption.

why?

Doubt is necessary to establish ‘anything at all in the sciences that is stable and likely to last’