Knowledge From Reason Flashcards
What is priori knowledge?
Knowledge that can be acquired without experience of the external world, through thought alone
E.g., working out what 5 + 4 is
What is a posteriori knowledge?
Knowledge that can only be acquired from experience of the external world
E.g., doing an experiment to discover the temperature at which water boils
Analytic vs Synthetic Truth
Analytic Truth - True in virtue of the meaning of the words
E.g., “A bachelor is an unmarried man” or “triangles have three sides”
Synthetic Truth - True in virtue of how the world is
E.g., “Grass is green” or “water boils at 100°c”
What is (rational) intuition?
A priori method for gaining knowledge:
The ability to know something is true just by thinking about it
E.g. Descartes’ cogito argument (I doubt therefore I think therefore I am)
What is deduction?
A priori method for gaining knowledge
A method of deriving true propositions from other true propositions (using reason)
E.g. You can use deduction to deduce statement 3 from statements 1 and 2 below:
1. If A is true then B is true
2. A is true
3. Therefore, B is true
Empiricism vs Rationalism
Empiricism says all a priori knowledge is of analytic truths (i.e. there is no synthetic a priori knowledge)
WHEREAS
Rationalism says not all a priori knowledge is of analytic truths (i.e. there is at least one synthetic truth that can be known a priori using intuition and deduction)
The Three Synthetic Truths Descartes Argues For
“I exist”
“God exists”
“The external world exists”
Descartes - Three Waves of Doubt
Illusion
Dreaming
Deception
Three Waves of Doubt: Illusion
I can doubt the reliability of my sense experience as it has deceived me in the past. For example, a pencil in water may look crooked even though it isn’t.
Three Waves of Doubt: Dreaming
I might believe I’m looking at a computer screen, but if I’m simply dreaming that I am, then my belief is mistaken.
Three Waves of Doubt: Deception
Basic ideas are still there in illusions and dreams such as 1+1=2 but Descartes says basic ideas can be doubted if you are being deceived.
E.g., I might believe I’m looking at a computer screen, but if I’m simply dreaming that I am, then my belief is mistaken.
Position of Extreme Doubt
Global Scepticism
Cogito Ergo Sum
I think therefore I am
Descartes — the only thing he can know for certain is:
Dubito, ergo cogito, ergo sum = I doubt, therefore I think, therefore I am
Descartes cannot doubt that he exists
Clear and Distinct Ideas
Recognition that it’s impossible for the proposition to be false
Descartes claims that his certainty in the proposition ‘I exist’ is due to the fact that it is a clear and distinct idea
Descartes’ 3 arguments for existence of God
Descartes gives several arguments for the existence of God using intuition and deduction:
• Descartes’ ontological argument
• Descartes’ cosmological argument
•The trademark argument
Summary of Descartes’ Trademark Argument
- I have the concept of God
- My concept of God is the concept of something infinite and perfect
- But I am a finite and imperfect being
- The cause of an effect must have at least as much reality as the effect
- So, the cause of my concept of God must have as much reality as what the concept is about
- So, the cause of my idea of God must be an infinite and perfect being
- So, God exists
Problem of The Trademark Argument
The concept of God is not innate - If concept of God comes from experience, as Locke argues, then Descartes’ argument is not entirely a priori and so fails to establish rationalism
Hume’s Fork
We can only have knowledge of:
- Relations of ideas
- Matters of fact
• Relations of ideas = a priori and analytic
• Matters of fact = a posteriori and synthetic
What is innate knowledge?
Knowledge you’re born with and so doesn’t require experience (a posteriori) to be known
Innate knowledge is a priori knowledge
Plato: Meno
Plato argues that all learning is a form of recalling knowledge from before we’re born. In other words, we’re born with innate propositional knowledge and we just need to remember it.
To prove his theory, Plato shows how Meno’s slave – a boy who has never been taught geometry – is able to understand a geometry proof.
Necessary truth
Leibniz argues that our knowledge of necessary truths must be innate.
Necessary truth= What must be the case
• True in every possible world
• E.g. “2+2=4” is true in every possible world – it must always be true
Contingent truth
Contingent truth = What is the case
• Could have been false in some other possible world
• E.g. “this website exists” is true but it would be false in some other possible world where I didn’t make it
What does Leibniz argue?
Leibniz argues knowledge of necessary truths is innate. We know them by paying close attention to “what is already in our minds”.
Arguments against innate knowledge (Locke’s arguments)
1. Innate knowledge would be universal
> Locke argues if we did have innate knowledge then every human would have such knowledge
Locke argues children and ‘idiots’ do not possess such knowledge – they don’t know the theorems of geometry, for example. So, this knowledge is not universal and therefore not innate.
2. Argument against innate concepts
Locke argues against the existence of innate concepts. The argument is that propositional knowledge relies on concepts. E.g., you can’t know that “1+1=2” without first having the concepts “1” ,“+”, and “2”. So, if Locke succeeds in disproving the existence of innate concepts, he will also succeed in disproving the existence of innate knowledge.
Normal incredulity/ordinary doubt
Doubts that occur in our everyday lives
E.g., you might be unsure whether a friend’s birthday is the 17th or the 18th of August
Examples of global sceptical scenarios in philosophy and popular culture
Descartes’ evil demon
The Matrix
The simulation hypothesis
Perfect virtual reality
Brain in a vat
