This is a dagger I see before me
no really is it
does the flammability of sensory evidence
the fact that we can make mistakes about what we're seeing
hearing touching tasting or smelling
does that mean that our senses are never reliable
well Macbeth was just hallucinating
but in ordinary life we can make mistakes too
I'll take this pencil for example
now I'm a magician
it looks bent doesn't it
but we know that's just an illusion
but if appearances can be deceptive
does that mean we should never trust them
surely that would make life unlivable
so generally we have to treat appearances as accurate
at least until experience proves otherwise
philosophers they're interested in getting behind appearances
we want to know what the truth is
how things really are
or if we can't discover that
we'd like the limits of what we can know
so that we can stop talking nonsense
in the worst case
we'd also like to know if we can't know anything at all
except the fact that we can't know anything at all
which would be disappointing but hey
we'd still like to know
so that's what we want to know
but can we know anything
imagine prisoners that have spent their entire lives chained
deep inside a cave
they have been changed so that they cannot see behind themselves
and they are forced to stare endlessly at the
cave wall in front of them
behind them a fire is burning
plato used the metaphor of a cave
to explain what he saw as the true nature of reality
most of us are like people change facing the wall of the cave
watching flickering representations on the wall
and taking these shadows for the real things
and not realizing it was the world outside the cave
philosophers however aren't so readily taken in by appearances
by the power of reason they get beyond the unreliable evidence to the senses and
think their way towards the truth
but surely I can know that I'm awake
I can know that I'm not dreaming can't I
well that's a hard
one I might feel that I'm awake
but most of us have had dreams in which we think we've woken up
but I'm really still asleep
so-called force awakenings
maybe that's happening now
perhaps I'm still really asleep
and perhaps you are too
but there are some things everyone knows
two plus two equals four
something as abstract as that must be beyond doubt
not necessarily
that's a shame
well what I was going to tell him is that:
I might just be a brain with electrodes stick me out of it
but an evil scientist manipulated my inputs
so that I have the illusion that two plus two equals four
when in fact it equals five
I know that's pretty unlikely but it can't be certain
that that's not what's happening
what would the evidence be
really clever scientist
might be able to give me a complete illusion of reality
and if this evil scientists who make me believe whatever she or he wants
then perhaps I can't be sure of anything
possibly not
but the great philosopher Rene Descartes had a
clever answer to that question
he called just about everything into doubt
until he could come up with something that he thought had to be true
and the rabbit he pulled out of his philosophical hat
I exist
or cogito ergo sum
as he putted in Latin
I think therefore I am
this must be true because in the very act of
questioning my own belief
and doubting that I exist
I prove that I do exist
I think I doubt therefore I exist
now I might not be able to say very much about what I am
I might not even exists as a body
and most or even all of my other beliefs might be delusional
but still as long as I doubt I exist
I must exist
but that answer
only leads to another question
even if I'm sure I do exist which I think I do
and therefore I am then Who am I
I can think
therefore I am
but what kind of I am I
you