René Descartes“Cogito, ergo sum.”

“I think, therefore I am.”

chief architect of 17th C intellectual revolution

laid foundations of ‘modern scientific age’

“The Father of Modern Philosophy”

Born Touraine, France “well-to-do” family Sent to school: studied mathematics, logic,

philosophy Impressed by “certainty” of mathematics Disappointed by philosophy, contained “no

point which was not disputed & hence doubtful.”

Background

True knowledge could only emerge from the power of human reason

At the age of 25, he decided:◦ He would no longer rely on ideas of other

philosophers (just because they were accepted authorities)

◦ To use his own rational powers to determine truth His major works:

◦ Discourse on Method (1637)◦ Meditations on the First Philosophy (1641)◦ Principles of Philosophy (1644)◦ Passion of the Soul (1649)

For Descartes

From Intuitive Certainty to Truth Recall: philosophers have long sought truth

& certainty Descartes eventually rejected ideas from

commonly accepted sources: they were uncertain & contradictory methods for determining truth

His conclusion: all knowledge began with ideas in the mind

Descartes’ Philosophy

“reject as absolutely false everything concerning which I could imagine the least ground of doubt.”

i.e, it is possible to doubt everything (shades of Chuang Tzu?)

He continued to seek one solid certainty upon which he could build knowledge

His “method”

He must exist In the act of doubting everything, there is a

being who doubts: “I think, therefore I am,” “Cogito, ergo

sum.” Certain that he exists, what else can he

know with certainty?

That single certain truth

In his thoughts, Descartes realized that he found the idea of God as an infinitely independent, all-knowing, and all-powerful being.

From where could this idea come? Since it cannot come from himself:

◦ an imperfect being such as himself could not have developed such an idea of perfection

◦ The idea must have come from God◦ Therefore, God must exist

God!

We have impressions of physical objects (sometimes against our will)

Is it possible that we are being fooled? Would God be deceiving us? No!

◦ God is perfect & wouldn’t want to deceive◦ Therefore external objects must exist!

Can Descartes be certain that external physical objects exist?

He existedGod existsExternal objects exist

3 Truths for Descartes (about which he is certain)

Orderly & systematic thinking Two major elements:

◦ Intuitive certainty◦ Deductive logic

Descartes believed: we can be certain of a truth when we recognize it intuitively, absolutely, and without question

E.g., our consciousness of our own existence,◦ 2 + 2 = 4, ◦ one cannot be in two different places at the same time, ◦ the parts of an object split in two pieces are smaller

than the original whole

Descartes’ Method

Intuitive certainty is an essential characteristic of truth

We use deductive reasoning to move with certainty from one truth to another

Deductive reasoning would mean if one accepts the premises, one would accept the conclusion

According to Descartes

Do not begin with what others say: begin with what is clear and certain

Reduce each step to its simplest components

Move step by step from easiest to more difficult ideas

Review carefully being careful to omit nothing

Stop when you arrive at a step is unclear

(read Meditations of First Philosophy excerpt on page 112)

The steps of His Method