Descartes

A Question

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

The Proper Purpose of Sensory Perceptions

‘the proper purpose of [...] sensory perceptions is simply to inform the mind of what is beneficial or harmful’

The Obscurity of Sensory Perceptions

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

Practicalities

Information about books, assessment and weekly tasks for the seminars.

The World: Light and Sound

‘It is possible for there to be a difference between the sensation that we have of it, and [...] what it is in the flame or in the Sun that we term ‘light’.’

Doubt

How did Descartes argue that sensory perceptions provide only very obscure information about the essential nature of bodies?

Cosmic Doubt

You are not in a position to know that you aren’t cosmically deceived on the basis of sensory perception alone. What follows?

I Exist

‘When someone says “I am thinking, therefore I am, or I exist,” he does not deduce existence from thought by means of a syllogism, but by a simple intuition of the mind’ (Second Replies).

Wax

‘even bodies are not strictly perceived by the senses or the faculty of the imagination but by the intellect alone’

Error

‘when I ... inquire into the nature of my errors [...] I notice that they depend on two concurrent causes, namely on the faculty of knowledge which is in me, and on the faculty of choice or freedom of the will; that is, they depend on both the intellect and the will simultaneously’ (Fourth Meditation).

Error (part II)

‘I can avoid error [...] merely [... by] remembering to withhold judgement on any occasion when the truth of the matter is not clear’ (Fourth Meditation).

Error and Clarity

‘whatever I perceive very clearly and distinctly is true’ (Third Meditation)

Error and the Senses

‘when I ... inquire into the nature of my errors [...] I notice that they depend on two concurrent causes, namely on the faculty of knowledge which is in me, and on the faculty of choice or freedom of the will; that is, they depend on both the intellect and the will simultaneously’ (Fourth Meditation).

The Senses and Appearances

‘when I see a stick, it should not be supposed that certain ‘intentional forms’ fly off the stick towards the eye, but 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, as I have explained at some length in the Optics. This movement in the brain, which is common to us and the brutes, is the first grade of sensory response.’

Refuted by Science?

Do any scientific discoveries about sensory perception conflict with Descartes’ claims about error?

Clear and Distinct

‘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’ (Principles of Philosophy CSM 1:207--8, AT VIII:21--22).

Do the Senses Deceive?

‘[F]rom time to time I have found that the senses deceive’ (Meditation 1), yet Sensory perceptions ‘do not represent anything located outside our thought’ (Principles).

Descartes’ Aim in The Meditations

‘these six meditations contain all the foundations of my physics ... they destroy the principles of Aristotle.’

Aristotelians vs Descartes on the Essential Nature of Bodies

Aristotle was wrong.

How to Write an Essay

‘these six meditations contain all the foundations of my physics. But please do not tell people’

The Natural Light and Natural Impulses

‘whatever is revealed to me by the natural light — for example that from the fact that I am doubting it follows that I exist, and so on — cannot in any way be open to doubt.’ (Third Meditation).

Is there a Cartesian Circle?

‘His circular bind, then, is that he can be absolutely certain about God only if he is already absolutely certain about clear and distinct ideas, and he can be absolutely certain about clear and distinct ideas only if he is already certain about God’ (Broughton 2003, p. 175).

A Puzzle about the Senses

Descartes appears to have endorsed claims with conflicting implications for whether sensory perceptions have intentional objects.

Conclusion

‘... the principal reason for doubt, namely my inability to distinguish between being asleep and being awake. For I now notice that there is a vast difference between the two, in that dreams are never linked by memory with all the other actions of life as waking experiences are’ (Meditation VI).