Lecture 08 | Descartes

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

So how did Descartes answer his question?

Through the intellect alone.

‘The only principles which I accept or require in physics are those of geometry and pure mathematics; these principles explain all natural phenomena, and enable us to provide quite certain demonstrations regarding them’

\citep[p.~247, AT 2:64]{descartes:1985_csm1}

Principles

Bennett Learning: ‘That plainly makes physics a part or a consequence of mathematics’

Clear and Distinct

How could the intellect alone enable us to know the essential nature of things?

‘I now seem to be able to lay it down as a general rule that

whatever I perceive clearly and distinctly is true’

(Meditation 3)

1. I clearly and distinctly perceive that I am a thinking thing.

2. This clear and distinct perception is enough for certainty.

3. Suppose not all clear and distinct perceptions were enough for certainty about what is perceived.

4. Then no clear and distinct perception would be enough for certainty.

5. But then my clear and distinct perception that I am thinking would not be enough for certainty.

6. Which it is.

7. So #3 leads to contradiction.

8. So all clear and distinct perceptions are enough for certainty.

recall from a moment ago

How could the intellect alone enable us to know the essential nature of things?

‘I am certain that I am a thinking thing.

Do I not therefore also know what is required for my being certain about anything?

In this first item of knowledge there is simply a clear and distinct perception of what I am asserting; this would not be enough to make me certain of the truth of the matter if it could ever turn out that something which I perceived with such clarity and distinctness was false.’

‘I now seem to be able to lay it down as a general rule that

whatever I perceive clearly and distinctly is true’

(Meditation 3)

At this point we face a flood of questions.

1. What are clear and distinct perceptions?

2. Why think perceptions which are not clear and distinct do not yield knowledge?

3. Why think clear and distinct perceptions do yield knowledge?

So far: on the basis of a single case study

So far: no reason

So far: the kind involved in cogito-style arguments

Let’s see whether we can get a bette sense by thinking about a particular case ...

recall from a moment ago

How could the intellect alone enable us to know the essential nature of things?

‘I am certain that I am a thinking thing.

Do I not therefore also know what is required for my being certain about anything?

In this first item of knowledge there is simply a clear and distinct perception of what I am asserting; this would not be enough to make me certain of the truth of the matter if it could ever turn out that something which I perceived with such clarity and distinctness was false.’

‘I now seem to be able to lay it down as a general rule that

whatever I perceive clearly and distinctly is true’

(Meditation 3)

Example: the wax

‘the perception I have of it is a case not of
vision or touch or imagination
... but of
purely mental scrutiny;

and this can be
imperfect and confused
as it was before

or
clear and distinct
as it is now,

depending on how carefully I concentrate’

Option 1: ‘clear and distinct’ is a psychological property

Option 2: ‘clear and distinct’ is a lose way of talking about whatever underpins mathematical knowledge

One attraction of this idea is that it gives us answers to all the questions ...

1. What are clear and distinct perceptions?

Those involved in thinking mathematically.

3. Why think clear and distinct perceptions do yield knowledge?

Because mathematics is possible.

Only problem is that physics does not reduce to mathematics. (Although Descartes might reasonably have thought otherwise.)

Option 1: ‘clear and distinct’ is a psychological property

Option 2: ‘clear and distinct’ is a lose way of talking about whatever underpins mathematical knowledge

Option 1: ‘clear and distinct’ is a psychological property

Option 2: ‘clear and distinct’ is a lose way of talking about whatever underpins mathematical knowledge

Dilemma: is your perception of the parallel posulate clear and distinct?

If not, you can never know which perceptions are clear and distinct.

If it is, not all clear and distinct perceptions yield knowledge.

Option 1: ‘clear and distinct’ is a psychological property

Option 2: ‘clear and distinct’ is a lose way of talking about whatever underpins mathematical knowledge

What do you think? Are either of these options viable? Is there another option?

What does Descartes himself say? Nothing much in the Mediatations. But

‘What is meant by a clear perception, and by a distinct perception.

I call a perception 'clear' when it is present and accessible to the attentive mind - just as we say that we see something clearly when it is present to the eye's gaze and stimulates it with a sufficient degree of strength and accessibility.

I call a perception 'distinct' if, as well as being clear, it is so sharply separated from all other perceptions that it contains within itself only what is clear’

\citep[pp.~207--8, AT VIII:21--22]{descartes:1985_csm1}

Descates (Principles of Philosophy)

No idea what to make of this.

Earlier I considered these questions. What have we learned?

1. What are clear and distinct perceptions?

2. Why think perceptions which are not clear and distinct do not yield knowledge?

3. Why think clear and distinct perceptions do yield knowledge?

Descartes is not super informative himself. I think you can read in what you like

Either no perceptions yield knowledge, or only perceptions of logical and perhaps mathematical truths.

You shouldn’t.

puzzle

A puzzle on Descartes’ positive views about how we acquire knowledge of the essential natures of things.

Descartes appears to hold that we have some kind of mathematical basis for knowledge of the essential natures of bodies. But he is also an early proponent of the importance of measurements. His scientific work all involves combining mathematics with observation. This is what led to the great breakthrough in science.

Hypothesis testing

1. Sensory perception alone cannot tell you which hypothesis is true.

2. Humans are disposed to accept many false hypotheses.

Therefore:

3. Your sensory perceptions and sense of what is plausible should not constrain which hypotheses you consider.

4. ... but observation (sensory perception) is essential for testing hypotheses.

xkcd.com/2115

[To illustrate that common sense shouldn’t be used in deciding which hypotheses to test.]

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

So here’s the question, as I keep saying.

Negative part

Negative part: full marks to Descartes

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

∴ Not by treating sensory perceptions as a basis for judgements about them.

Positive part: descartes is just wrong

Positive part

Through the intellect alone.

method: take only what is good, waste no time on flaws

This is why we will not consider Descartes’ arguments for the existence of god on this course, for example. I can find nothing of value in them. Of course I might easily be wrong.

Closing fun ...

‘The [...] natural light [...] enables me to perceive that I would have given myself all the perfections of which I have an idea, if I had given myself existence’

(Fourth Replies).

‘the learned often employ distinctions so subtle that they disperse the natural light, and they detect obscurities even in matters which are perfectly clear to peasants’

\citep[p.~59]{descartes:1985_csm1}

(Rule 14).

Do the Senses Deceive?

Sensory perceptions of tastes, smells, sounds, heat, cold, light, colors and the like ‘do not represent anything located outside our thought’

Principles

(\citealp[p.~ 219, AT VIII:35]{descartes:1985_csm1} cited by \citealp[p.~348]{simmons:1999_are})

How to resolve the puzzle?

‘when I see a stick, it [is] simply that rays of light are reflected off the stick and set up certain movements in the optic nerve and, via the optic nerve, in the brain

This movement in the brain ... is the first grade of sensory response.

the second grade ... extends to the mere perception of the colour and light reflected from the stick [...]

Nothing more than this should be referred to the sensory faculty, if we wish to distinguish it carefully from the intellect.

But suppose that ... I make a rational calculation about the ... shape ... of the stick:

although such reasoning is commonly assigned to the senses (which is why I have here referred it to the third grade of sensory response), it ... depends solely on the intellect.

Sixth Replies

Sensory perceptions of tastes, smells, sounds, heat, cold, light, colors and the like ‘do not represent anything located outside our thought’

Principles

(\citealp[p.~ 219, AT VIII:35]{descartes:1985_csm1} cited by \citealp[p.~348]{simmons:1999_are})

‘from time to time I have found that the senses deceive’

\citep[p.~17, AT VII:18]{descartes:1985_csm2}

Meditation 1

How to resolve the puzzle? Descartes is talking in the ordinary way, where such reasoning is ‘commonly assigned to the senses’ He doesn’t really mean it.

Or?

Always consider objections to your views!

In the Sixth Meditation, Descates returns to the topic and appears to say that the sense do deceive.

‘there may be some occurrence, not in the foot but in one of the other areas through which the nerves travel in their route from the foot to the brain, or even in the brain itself; and if this cause produces the same motion which is generally produced by injury to the foot, then pain will be felt as if it were in the foot. This deception of the senses is natural’ \citep[p.~61, AT VII:88]{descartes:1985_csm2}.

‘there may be some occurrence, not in the foot but in one of the other areas through which the nerves travel in their route from the foot to the brain, or even in the brain itself;

and if this cause produces the same motion which is generally produced by injury to the foot, then pain will be felt as if it were in the foot.

This deception of the senses is natural’

Sixth Meditation

Can we explain this away using the same strategy (ie its the third grade of sensory response)?

On Descartes’ view, can the senses deceive?

Sensory perceptions of tastes, smells, sounds, heat, cold, light, colors and the like ‘do not represent anything located outside our thought’

Principles

(\citealp[p.~ 219, AT VIII:35]{descartes:1985_csm1} cited by \citealp[p.~348]{simmons:1999_are})

‘from time to time I have found that the senses deceive’

\citep[p.~17, AT VII:18]{descartes:1985_csm2}

Meditation 1

‘pain will be felt as if it were in the foot [...] This deception of the senses is natural’

Meditation 6

How to resolve the puzzle?

Lecture 08:

Descartes

[email protected]

Clear and Distinct

Do the Senses Deceive?

Keyboard Shortcuts?

Lecture 08:

Descartes

[email protected]

Clear and Distinct

Do the Senses Deceive?

Keyboard Shortcuts`?`