The Limits of Knowledge
(incomplete)
The topics in Epistemology so far have covered how it is we are supposed to be able to know things. This topic examines the limits to this. What can we reasonably know and why are their limits to our knowledge?
Scepticism vs Normal Incredulity
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Scepticism in philosophy involves casting doubt on our claims to knowledge and questioning whether we can truly know anything at all.
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It focuses on abstract, foundational questions about perception, justification, and the limits of human understanding.
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Normal incredulity is the everyday doubt we have about practical matters, things like whether someone is telling the truth or whether an event really happened.
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Normal incredulity operates within assumptions we take for granted. It depends on beliefs that philosophical scepticism challenges, such as that we have a body, reliable senses, and veridical experiences.
Local vs Global Scepticism
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Local scepticism targets a particular claim or a specific domain of knowledge.
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This happens when our reasons for doubt apply only to certain types of belief.
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Global scepticism challenges the possibility of any knowledge at all by undermining all beliefs equally.
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Nick Bostrom’s simulation hypothesis is a modern example of Global Scepticism, which questions whether we can know that our entire reality isn’t an artificial simulation:
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P1: It is technologically possible for minds to be simulated on computers.
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P2: If a civilisation reaches a sufficiently advanced stage, it will run these simulations which contain minds with conscious experiences that are indistinguishable from our own.
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P3: This will happen so often that the number of simulated worlds would end up exceeding the number of non-simulated worlds (our one).
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C: Therefore, by probability alone, it is more likely that we are in a simulated world than in the single original world.
Descartes' Three Waves of Doubt
First wave: doubting your senses
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Our senses sometimes deceive us.
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Have you ever thought you have seen someone and then it turned out to be someone else? Have you thought that you heard someone calling your name but no one did?
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Any knowledge derived solely from sensory experience could be unreliable.
Second wave: Dreaming
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There is no certain way to distinguish being awake from dreaming.
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Even vivid sensory experiences could be part of a dream.
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This calls into question all beliefs about the external world and bodily existence.
Third wave: The Malicious Deceiver
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A powerful, deceitful being could manipulate our thoughts, making even mathematics and logic unreliable.
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This is the most radical form of doubt, casting uncertainty over even the most certain seeming knowledge.
Response: Descartes
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1.) Descartes’ Cogito argument shows that, even if he is being tricked by a malicious deceiver, he can at least be certain of the proposition ‘I exist.’
I doubt; therefore I think; therefore I am
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Even if the worst case were true and there were a malicious deceiver, there has to be something for the deceiver to trick in the first place. The very fact that Descartes can doubt, proves his own existence.
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2.) He then argues that he can also know that God exists.
This is Descartes' Ontological Argument.
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3.) Descartes then goes on to reason that the external world must also exist:
P1.) I experience perceptions that appear to come from an external world.
P2.) Because these perceptions happen involuntarily, they cannot be produced by my own mind.
C1.) Therefore, their cause must be external.
P1.) Since God exists, if God were the direct cause of these perceptions rather than physical objects, God would be deceiving me about the existence of an external world.
P2.) But a perfect God would not deceive me.
C2.) So my perceptions are trustworthy, and from this I can know that an external world of physical objects exists.
Responses to Scepticism
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Bertrand Russell: the existence of an external world was the best hypothesis. Yes, we can’t know for certain that we’re not being deceived by an evil demon, but we can still have knowledge. An external world is also a better explanation of our experiences.
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John Locke: The coherency of sense perception and involuntary perceptions are Locke's two arguments for the existence of a mind-independent world as seen in the Knowledge via Perception section.
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Berkeley: God continually causes our perceptions, but this isn’t deceptive. Our perceptions simply are reality (to be is to be perceived). Because of this, global scepticism fails. There’s no gap between how things appear and how they really are. Reality is perception.