1. Descartes & Rationalism

2. Rene Descartes

3. Basic Data Frenchman 1596-1650 Catholic Renaissance man
Mathematics
Science
Philosophy
Lived most of his life in Holland
Died in Sweden after traveling there to tutor the queen in philosophy

4. Critique of Scholasticism
Opposed “substantial forms” or “universals”
Principle for organization of data
Saw final cause as the main purpose of being
Example: A swallow flies for the sake of (because it is) a swallow
The swallow’s purpose is to fly
Example: An iPod is an iPod because it does what an iPod does and so fulfills the purpose or end of iPodness.
Other tablets may fulfill the purpose of an iPod, but only iPods fulfill iPodness completely.
Descartes’ criticism
true, but does not provide new or useful knowledge
Better: consider and deduce from individual thing

5. Critique of Scholasticism
In the Sixth Replies, Descartes uses the Scholastic conception of gravity in a stone, to make his point. On this account, a characteristic goal of being a stone was a tendency to move toward the center of the earth. This explanation implies that the stone has knowledge of this goal, of the center of the earth and of how to get there. But how can a stone know anything, since it does not think? So, it is a mistake to ascribe mental properties like knowledge to entirely physical things. This mistake should be avoided by clearly distinguishing the idea of the mind from the idea of the body. Descartes considered himself to be the first to do this. His expulsion of the metaphysical principles of substantial forms and final causes helped clear the way for Descartes’ new metaphysical principles on which his modern, mechanistic physics was based. (Skirry,

6. Critique of Scholasticism
Opposed the notion that all knowledge comes from the senses
Descartes’ criticism
Senses can deceive; therefore, they are not a reliable source for knowledge
Propositions based on sense knowledge (id est, a posteriori) are, by nature, probabilistic and therefore doubtful
Just because I see you drop a pen and it lands on the floor does not mean that it will land on the floor the next time you drop it.
Influences Hume
For this reason, Descartes sought not Truth but certainty
Mathematics provides certainty

7. A Priori Propositions “Some ideas are true independent of experience”.
Descartes did not deny that the senses give us important information about the world. But senses are not the sole, or even the most important, means of knowledge.
The senses mislead us.
Therefore, knowledge which is independent of experience must be more trustworthy because it has less to do with the senses.
Mathematical propositions (2 + 2 = 4).
Things which are true by definition (all bachelors are unmarried).
Self-evident truths (such as “I think therefore I am” or “God exists”).

8. A Priori Propositions
Based on notion that mathematics is “more pure” than Geography or physics.
A priori propositions are unchanging laws
Conclusion: Innate ideas are unchanging laws, and so they are a more sound or certain foundation for knowledge
Innate ideas never change
Innate ideas are the same regardless of person, era, location, etc.

9. How Can I be Certain? Notice the question.
Subjective
Like Luther’s question, “How can I know there is a loving God?”
KEY: Not what is, but what I can be sure of
Notice the assumption: Descartes seeks not Truth but Certainty
KEY: I can never be certain that things actually are as they appear
“Things are not always what they seem; the first appearance deceives many; the intelligence of a few perceives what has been carefully hidden.” (Phraedus; 15 BC-50 AD)

10. Two Conjectures Dream Conjecture Evil Demon Conjecture
For all I know, I may be dreaming. All reality may be a dream.
Why? Because my senses can deceive me.
Evil Demon Conjecture
For all I know, all reality may have been planted in my mind by an evil
Therefore, all lies are true, and all truths are lies.
Question: So how do I know for certain what is real?
Cogito, ergo sum.
Remember St Augustine: Doubt proves that I am real.
What Descartes meant is that any attempt to doubt one’s existence as a thinking being is impossible because to doubt is to think and to exist.

11. Summary
Assumption: Senses can deceive us; therefore, primary source of information about reality is not reliable. Therefore, the senses cannot provide certain knowledge.
Dispatches “naïve realism” (what you see is what you get)
Axiom: What we perceive is subjective. Therefore, what we perceive gives us no certain knowledge of the outside world.
Not how we interpret the data, but how we take it in (like a photo or video)
Descartes: Solipsism is correct – have students look up and define

12. Summary
Sense data can give certain knowledge only because knowledge is based on four innate ideas
Selfhood – the contents of my mind are all I have to work with; hence I am working /thinking within myself
Identity (sameness) – the ability to classify like things
Substance (“thingness”) – despite change, a thing remains the same thing
All-Perfect being – that there is a God; which relies on 2 arguments
Ontological argument (Anselm)
Cartesian proof (see Palmer, 174)

13. Results What makes Descartes a modern thinker or philosopher?
Appeal to reason, rather than authority (modified form of logos vs. mythos)
Focus on subject rather than object
Ascendency of individualism as a perspective for philosophy
Affects politics (rights), religion (reformation); becomes basis for existentialism
Descartes Metaphysics and results
What are innate ideas?
Are they substances?
What is a substance?