Philosophical Scepticism

Outline the 3 waves of doubt - dream

P1. In order to know about the nature of the external world , I need to be certain I am not dreaming

P2. In order to be certain , dreams would have to be subjectively distinguishable from veridical experience

P3. Vivid dream subjectively indistinguishable from a possible veridical experience

C. Therefore , I cannot be certain I am not dreaming now , so I cannot know anything of what the external world is like

Outline 3 waves of doubt - evil demon

P1. Possible evil demon continuously deceiving me of all my perceptions so everything true is false

P2. Know anything need to rule this out

P3. Cannot rule this out , whether my experience true/false my experience would stay the same .

C. Therefore , cannot know anything

What can Descartes conclude from the 3 waves of doubt ?

“ Cogito ergo sum “ I think therefore I am

I think therefore if i am thinking I must exist

a priori knowledge

Define philisophical scepticism

Doubt that we experience about our grounds to knowledge such as is an evil demon decieving us

Define global scepticism

These are doubts which we experience which question our grounds to knowledge such as if an evil demon deceiving us .

Question if we can know anything .

Define local scepticism

These are everyday doubts we experience such as if I left my oven on or have done my homework . These do not question our grounds to knowledge or whether we really exist .

Define normal incredulity

These are everyday doubts we experience such as if I left my oven on or have done my homework .

These do not question our grounds to knowledge or whether we really exist

Outline 3 waves of doubt - illusion

P1: In order to know about the nature of the external world , I need to be certain that I am not currently subject to an illusion

​P2: In order to be certain that I am not experiencing an illusion, illusions would have to be clearly different from true experiences.​

​P3: Some illusions are subjectively indistinguishable from true/veridical experiences.​

​C: Therefore, I cannot be certain that I am not now experiencing an illusion, and so I cannot know anything about what the external world is like

What is Hume’s response to cogito ergo sum?

All concepts are copies of sense impressions

Cannot have a sense impression of the self as we observe heat , pleasure , anger

The self is not a clear and distinct concept but a bundle of impressions

Outline Descartes intuition and deduction The Trademark Argument as an a priori deduction

P1. The cause of anything must be at least as perfect as its effects

P2. My ideas must be caused by something

P3. I am an imperfect being

P4. I have the idea of God , which is that of a perfect being

C1. I cannot be the cause of my idea of God

C2. Only a perfect being ,God, can cause the idea of God

C3. God must exist

Outline the criticism that the causal adequacy principle may not be true

Descartes claims “the total cause of something must contain at least as much reality as does the effect.”

But some effects seem to be greater than their causes e.g. a powerful avalanche caused by a small whisper.​

How would Descartes respond to the criticism of the casual adequacy ?

However, Descartes would reply that the whisper is not the “total cause” here – it is merely the trigger.

But the cause also includes the build up of snow, gravity and so on. ​

Outline the criticism that we do not have a clear idea of an infinite being of the Trademark argument ?

Descartes claims he has a “clear and distinct” idea of an infinitely powerful God.

However, this is by no means self-evident.​

Many theist philosophers (who believe in God) argue that God’s greatness is beyond comprehension, and the best we can do is understand it by analogy/comparison with attributes we know of – power, love, knowledge.​

Outline the criticism for the Trademark argument that the idea of God is incoherent

Descartes claims he has a “clear and distinct” idea of an infinitely powerful God.​

However, the paradox of the stone shows the idea of God as omnipotent is incoherent :

P1. If God is omnipotent he can create a stone too heavy for him to lift.​

P2. But if he can create it, there is something he cannot do, and if he cannot create it there is something he cannot do.​

C. Therefore, God cannot be omnipotent. ​

How would reliabilism respond to scepticism​

Scepticism rests on the idea that we must have internal reasons showing that we know when we have knowledge

i.e. that we can justify when we have knowledge, but the reliabilist drops this requirement and just says that as long as the process that leads to the belief is generally reliable (mostly produces truth), then you don’t need to know that you know.​

​For instance, as long as I get mushrooms that don’t poison me (i.e. I have a reliable process for getting the truth), I don’t need to know the details of why certain mushrooms are edible and others poisonous. ​

Define internalism

To justify our knowledge we must have internal reasons, beliefs or justification that we can reflect on.​

E.g. Descartes’ introspective knowledge that he is a thinking thing.​

Define externalism

To justify knowledge we do not need internal reasons, we merely need to consistently get to the truth.​

E.g. my dog consistently knows where the food is, his name and his owner as he responds correctly and reliably to all these.​