1. On your whiteboard: What is empiricism? Arguments/evidence for it?
Arguments/evidence against it?
Which is more convincing so far, empiricism or innatism?

2. Objectives Understand Descartes’ rationalism
Know the key strengths and weaknesses
Begin to evaluate it against innatism and empiricism

3. Rationalism
We can have real knowledge about the world that is not based on experience, but on reason.
This is not innate. We know it through rational intuition & deduction
Rational intuition
Being able to understand something just by thinking about it
Deduction
Figuring out what must follow from certain claims

4. Descartes’ sceptical argument: 3 waves of doubt
Knowledge requires certainty.
Senses?
Illusions, hallucinations
What can we be certain of?
External world?
Dreaming
Truths of maths?
Evil demon

5. The cogito argument
Knowledge must be built on secure, indubitable foundations
I can doubt that any of my physical experiences are real.
IC. Therefore my physical sensations cannot give me knowledge.
I know that if I am doubting there must exist an “I” that doubts.
MC: Therefore I know through thinking alone, that I exist, as a purely mental thing.

6. Think-Pair-Share
What do you like / dislike about the argument for a priori knowledge of self?
Is Descartes right…
That we can doubt everything to do with the senses?
That we must exist because we experience doubt?
That if we do exist we must be non-physical
That we don’t need any experience of the world to know this?

7. Descartes now puts forward an argument to show that we can derive knowledge of the existence of God and of the external world from this indubitable knowledge of our own existence.
So, the argument aims to show that we can have a priori synthetic knowledge…

8. Important Information: Clear and Distinct ideas
The next step in Descartes depends on his concept of ‘clear’ and ‘distinct’ ideas. These are ideas that are:
Clear – An idea is clear ‘when it is present and accessible to the attentive mind’ – just as we say we see something clearly when it is present to the eye’s gaze.
Essentially they are those ideas we can see clearly in the mind, without any external influence.
Distinct – An idea is distinct if it is clear and ‘it is so sharply separated from all other ideas that every part of it is clear’.
This just means we can have the idea clear in our minds without it depending on any other ideas or feelings we may have.
Descartes believes the Cogito, along with simple truths of geometry and mathematics are clear and distinct. We can understand them clearly with no external experience and things like 2+2=4 can be isolated from any other knowledge or concepts.

9. Clear and Distinct ideas
Knowledge of oneself (the cogito) is clear and distinct (self- evident)
Whatever is clear and distinct like this must be true and cannot be doubted (i.e. it is knowledge)
The idea of God is clear and distinct. So God exists. (trademark argument)

10. Premise 1: The cause of anything must be at least as perfect as its effect.
Premise 2: My ideas must be caused by something.
Premise 3: I am an imperfect being.
Premise 4: I have the idea of God, which is that of a perfect being.

11. Premise 1: The cause of anything must be at least as perfect as its effect.
Premise 2: My ideas must be caused by something.
Premise 3: I am an imperfect being.
Premise 4: I have the idea of God, which is that of a perfect being.
Intermediate Conclusion 1: I cannot be the cause of my idea of God (from premises 1,2,3 & 4)
Intermediate Conclusion 2: Only a perfect being (that is, God) can be the cause of my idea of God. (From premises 1, 4 and IC1)
Main Conclusion: God must exist. (From premise 4 and IC2)

12. 4. God is good, and would not allow us to be deceived like that!
What if we are being deceived to think that clear and distinct ideas must be true?

13. A priori knowledge of the external world
5. The idea that things in the world exist is clear and distinct
Why?

14. A priori knowledge of the external world
5. The idea that things in the world exist is clear and distinct
Why?
Conclusion: I can know, using reason alone and without relying on the senses, that I exist, that God exists, and that the external world exists.
The wax argument
Nothing I sense stays the same
Yet I know that it is the same thing
Therefore my knowledge of things existing must be based not on sense experience, but on deduction
So I can have a priori knowledge of the external world

15. On your whiteboards:
Draw a flowchart to show how Descartes’ arguments progress from each other
One similarity between rationalism and innatism, and one difference
One strength of rationalism over innatism
One issue with rationalism

16. Circular reasoning
We know God exists because it is self-evident – it is a clear and distinct idea
We know clear and distinct ideas are true because God wouldn’t allow us to be deceived

17. Descartes’ response:
There are some propositions so clear and distinct that they are self-guaranteeing, even without relying on God’s goodness.
Examples?
2+2=4
If I think, I exist

18. Counter-response to Descartes:
These examples are merely analytic!
They don’t tell us anything about the world, only about the meaning of the words within the propositions.

19. Is there any a priori synthetic knowledge?
Which side is the strongest so far? Why?
Where does this leave us?
Or in other words…
Which is the strongest argument in favour of a priori synthetic knowledge?
Which is the strongest criticism of a priori synthetic knowledge?
So… which side is strongest overall – for or against?