René Descartes (1596-1650)René Descartes (1596-1650)

The popular version of The popular version of DescartesDescartes

Meditations on First Meditations on First Philosophy (1641)Philosophy (1641)

One of only four works published during One of only four works published during Descartes’ lifetime (the others are Descartes’ lifetime (the others are DiscourseDiscourse [1637], [1637], PrinciplesPrinciples [1647], [1647], Passions of the SoulPassions of the Soul [1649] [1649]

His most enduring work, but not that one His most enduring work, but not that one on which his historical reputation was on which his historical reputation was foundedfounded

Better known in his own time as a Better known in his own time as a practicing scientistpracticing scientist

Examples of the scientific Examples of the scientific workwork

Illustration (and the Illustration (and the one following) is from one following) is from the 1637 edition of the 1637 edition of the the DiscourseDiscourse; ; explanations here of explanations here of focus, reflection, focus, reflection, refractionrefraction

Example (cont’d.)Example (cont’d.)

Here Descartes uses Here Descartes uses the theory of optics the theory of optics (as in the previous (as in the previous example) to give an example) to give an explanation of the explanation of the phenomenon of the phenomenon of the rainbowrainbow

What is the purpose or aim of What is the purpose or aim of the Meditations?the Meditations?

The ‘narrow’ agenda: to provide a solid The ‘narrow’ agenda: to provide a solid justificatory framework for doing natural justificatory framework for doing natural science.science.

The wider agenda: to show that we indeed The wider agenda: to show that we indeed do, as against the claims of skepticism, do, as against the claims of skepticism, have knowledge, and that a theory of have knowledge, and that a theory of knowledge need not fall prey to the infinite knowledge need not fall prey to the infinite regress or the circular argumentregress or the circular argument

What is the methodology of What is the methodology of the Meditations?the Meditations?

““inasmuch as reason already persuades inasmuch as reason already persuades me that I ought not less carefully to me that I ought not less carefully to withhold my assent from matters which are withhold my assent from matters which are not entirely certain and indubitable than not entirely certain and indubitable than from those which appear to me evidently from those which appear to me evidently to be false, if I am able to find in each one to be false, if I am able to find in each one some reason to doubt, this will suffice to some reason to doubt, this will suffice to justify my rejecting the whole.” justify my rejecting the whole.”

Methodology of the Methodology of the Meditations (cont’d.)Meditations (cont’d.)

““for that end it will not be requisite that I for that end it will not be requisite that I should examine each in particular, which should examine each in particular, which would be an endless undertaking; for would be an endless undertaking; for owing to the fact that the destruction of the owing to the fact that the destruction of the foundations of necessity brings with it the foundations of necessity brings with it the downfall of the rest of the edifice, I will only downfall of the rest of the edifice, I will only in the first place attack those principles in the first place attack those principles upon which all my former opinions rested.” upon which all my former opinions rested.”

Methodology of the Methodology of the Meditations (cont’d.)Meditations (cont’d.)

Descartes uses the method of what is Descartes uses the method of what is sometimes called sometimes called hyperbolic doubthyperbolic doubt (i.e. (i.e. exaggerated doubt for a specific purpose); exaggerated doubt for a specific purpose); he does he does notnot say “doubt everything” or say “doubt everything” or “treat every former opinion as false”, but “treat every former opinion as false”, but rather “doubt everything or treat everything rather “doubt everything or treat everything as false as false until proven otherwiseuntil proven otherwise”.”.

Q: What is the virtue, if any, of such a Q: What is the virtue, if any, of such a method?method?

Casting the skeptical netCasting the skeptical net

Descartes goes after “the principles upon Descartes goes after “the principles upon which all my former opinions rested.” What which all my former opinions rested.” What are those? are those?

1. Those things “I have learned either from 1. Those things “I have learned either from the senses or through the senses.”the senses or through the senses.”

Are there any reasons for doubting beliefs Are there any reasons for doubting beliefs acquired in this way? A: yes, there are.acquired in this way? A: yes, there are.

IllusionIllusion

More illusionMore illusion

The coloured lines in The coloured lines in both pictures are the both pictures are the same; the only same; the only difference is the black difference is the black bar in the lower bar in the lower image. image.

Casting the skeptical net Casting the skeptical net (cont’d.)(cont’d.)

In addition to optical illusion, Descartes appeals In addition to optical illusion, Descartes appeals to various other instances where we can be to various other instances where we can be mislead by sensory information – obscure mislead by sensory information – obscure conditions, hallucination, phantom pains – all of conditions, hallucination, phantom pains – all of which it is possible dismiss as cases of non-which it is possible dismiss as cases of non-optimal or non-standard conditions of perceptionoptimal or non-standard conditions of perception

Q: if ‘optimal’ conditions are those where we Q: if ‘optimal’ conditions are those where we don’t go wrong, how can we sure we’re in the don’t go wrong, how can we sure we’re in the optimal situation? optimal situation?

Casting the skeptical net Casting the skeptical net (cont’d.)(cont’d.)

However much we might come to doubt the However much we might come to doubt the reliability of sense information (and, at least reliability of sense information (and, at least provisionally, treat all such information as false), provisionally, treat all such information as false), there is a great deal we might still claim to know there is a great deal we might still claim to know even under non-optimal conditions.even under non-optimal conditions.

2. 2. The dream hypothesisThe dream hypothesis: “there are no certain : “there are no certain indications by which we may clearly distinguish indications by which we may clearly distinguish wakefulness from sleep” But if I don’t know that I wakefulness from sleep” But if I don’t know that I am not now dreaming, how do I know that there am not now dreaming, how do I know that there is an external world at all?!is an external world at all?!

Casting the skeptical net Casting the skeptical net (cont’d.)(cont’d.)

Again, even if we accept that we might presently Again, even if we accept that we might presently be dreaming, still there are ‘truths’ (knowledge be dreaming, still there are ‘truths’ (knowledge items, if you will) that escape even this fine a net items, if you will) that escape even this fine a net (e.g. 2 +2=4)(e.g. 2 +2=4)

3. 3. The ‘evil genius’ hypothesisThe ‘evil genius’ hypothesis: What if, instead : What if, instead of God, there is an anti-God, who can cause me of God, there is an anti-God, who can cause me to be certain even where what I most certain to be certain even where what I most certain about is false? What then? Is nothing certain about is false? What then? Is nothing certain then? Happily, there is a solution.then? Happily, there is a solution.

Resolving the skeptical Resolving the skeptical dilemma or, escaping the netdilemma or, escaping the net

The challenge of the evil genius hypothesis is The challenge of the evil genius hypothesis is that we might be certain about something which that we might be certain about something which is false. But there is at least one thing about is false. But there is at least one thing about which we can be certain, which we can be certain, even ifeven if we doubt it, and we doubt it, and that is that we exist (for we must exist, if we are that is that we exist (for we must exist, if we are doubting) doubting)

This is Descartes’ ‘Archimedean’ point; it shows This is Descartes’ ‘Archimedean’ point; it shows that at least one thing escapes the skeptical net.that at least one thing escapes the skeptical net.

Q: Is this enough? Is it sufficient to know this Q: Is this enough? Is it sufficient to know this one (fairly obvious) thing?one (fairly obvious) thing?