When talking about scepticism, we should begin by making a distinction between normal incredulity
and philosophical scepticism.
The first refers to doubt about commonplace everyday questions about human life and the kinds of
practical considerations that happen to matter in that context. For example, you can be incredulous
about a friend saying that they ‘found the cure for cancer’, because of the set of probabilistic
judgements you’ve acquired about life and the world.
Whereas the latter is concerned with whether we can hold any knowledge at all, regardless of its
significance for human life.
Throughout this essay, I will show how global scepticism can be overcome, as an issue which arises
only if taken as a definition of knowledge ‘Infallibilism’, which for the sake of philosophical debate is
not viable.
We should understand the role of scepticism within epistemology as a challenge: the sceptic doesn’t
suggest that there is any reason to believe in the sceptical possibilities of thought experiments, but
requests that we rule them out as possibilities.
When dealing with scepticism, we should differentiate between local scepticism, i.e. about a particular
claim (e.g. a particular sense experience) or domain of claims (e.g. all sense experiences), and global
scepticism which undermines all possible knowledge claims.
For example, philosophical scepticism asks you to rule out the possibility that we could be a brain in a
vat, manipulated by scientists to have the perceptual experiences of e.g. talking and walking. This
scepticist claim could even be extended by saying that scientists may also be feeding us memories, or
even thoughts, and therefore we cannot be sure even about what is in our thoughts.
Moreover, it could be argued that even if we are not a brain in a vat, and reality is actually as we think
it is, our true belief would lack a justification, and therefore cannot be considered knowledge.
This is an example of global scepticist claim, as we cannot be sure about whether we are brains in a
vat or not, and therefore all our knowledge is doubted.
In favour of this global scepticist position we may find Descartes’ three ways of doubt, which lead to
the conclusion that we have no certain knowledge at all, as there is nothing we cannot doubt.
1. His first argument is the ‘Illusion argument’, which goes as follows:
It seems that, if we have certain knowledge, then it would be knowledge from the senses, because I
normally appeal to the senses in order to confirm things I am not sure about.
However, I know that in the past my senses have deceived without me realising it. Therefore, at any
moment it is possible that my sense are deceiving me without me realising it. Therefore, I can always
doubt my senses.
Therefore, my senses do not give me certain knowledge.
2. Descartes then continues with his ‘Dreaming argument’, which runs as follows:
Even though my senses sometimes deceive me, this doesn’t show that they always deceive me, and it
seems that some sense experiences are so clear and vivid that I cannot doubt them.
However, sometimes I have a clear and vivid sensation in a dream, when I am not aware that I am
dreaming.
Therefore, I can doubt whether any of my sensations correspond to reality. So, it seems that I indeed
have no certain knowledge.
3. The philosopher then ends with his ‘Evil demon argument’, which argues:
It seems as though, even if I am dreaming, I do know some truths about the real world, because in
order to have my dreams, I must be drawing upon shapes and colours from my experience, so these
must exist in the real world.
However, it is possible that there exists an evil demon who can put away any thought whatever into
my mind. So, I can doubt anything in my mind at all.
So, it seems that we can doubt everything, because an evil demon can make me think what is false.
