Descartes’ Radical Doubt
Blank Slate vs. Hard Wired
When we come into the world
at birth, the mind is like a
blank tablet.
Or
Some ideas are directly
known by the mind and are
not learned from experience:
a. the laws of logic; b. the
basic principles of
mathematics; c. cause/effect;
d. concept of perfection; e.
idea of God; f. moral
concepts.
Knowledge, Probability, and Certainty
Our knowledge of reality can
never be absolutely certain.
However, if a belief is true and
we have sufficient evidence of
its probability, we have
knowledge.
or
Through reason, it is possible
to have knowledge about
reality that is absolutely
certain.
Is the Problem of Knowledge Really a Problem?
If we are born “blank
slates,” what obligations do
we have to ensure that all
have equal opportunity to
gain knowledge?
If nothing can ever be
known, how can anything
ever be condemned,
celebrated, or
communicated?
If knowledge about the
nature of reality is primarily
a priori, how should
children be educated?
If certainty is impossible, by
what criteria do we claim
that a belief is justified?
God and Religion
1= I do have knowledge.
2 =Knowledge is possible but I don’t
know the answer.
There is a God.
Supernatural miracles do
not occur.
3=Knowledge is impossible.
There is life after death.
One particular religion is
the true one.
4-6=very confident
10-12=very skeptical
Science
1= I do have knowledge.
2 = Knowledge is possible but I don’t know the
answer.
3=Knowledge is impossible.
Science gives us the best
information about reality.
Science can tell us about the
origins of the universe.
Science can tell us about the
origins of human life.
Scientists will one day be able
to explain all human behavior.
4-6=very confident
10-12=very skeptical
Moral Knowledge
1= I do have knowledge.
2 = Knowledge is possible but I don’t
know the answer.
3=Knowledge is impossible.
Some actions are objectively
right or wrong.
The convention of one’s
society determine what is
right or wrong.
Pleasure is the only thing in
life that has value.
Sometimes it could be one’s
moral duty to lie.
4-6=very confident
10-12=very skeptical
Skepticism
Sense organs are unreliable.
Sense data is not the thing.
We cannot get outside of our minds or
experiences to verify that what we claim
is true is, in fact, true.
We “know” only our individual thoughts
(which is really to say that we think).
Universal skeptics: no one knows
anything.
You claim to know
what????
Limited skeptics: some claims to
knowledge are doubtful.
Strategies of the Skeptic
Universal Belief Falsifiers
It is theoretically possible that
X [I’m a figment of your
imagination, you’re a brain in a
vat, our eyes distort images of
the material world, we’re in
the matrix, you’re dreaming,
etc.].
If X were the case, we would
have no way of knowing it.
Since we have no way of
knowing whether X is the
case or not, we cannot know
whether claims related to or
dependent upon X are true or
false.
Therefore, we have no
knowledge.
Another Strategy of the Skeptic
You claim to know, so prove it.
And while your at it, tell me
why my arguments for doubt
are wrong.
If you have no fail-safe method
for establishing whether
something is true or false, then
you have no justification for
claiming to know that
something is true or false.
Generic Skeptical Argument
1. We can find reasons for doubting
any one of our beliefs.
2. It follows that we can doubt all
our beliefs.
3. If we can doubt all our beliefs,
then we cannot be certain of any
of them.
4. If we do not have certainty about
any of our beliefs, then we do not
have knowledge.
5. Therefore, we do not
have knowledge.
Descartes’ Method
“Some years ago I was struck by
the large number of falsehoods
that I had accepted as true in my
childhood, and by the highly
doubtful nature of the whole
edifice that I had subsequently
based on them.”
Examples of falsehoods?
Radical Doubt
“Reason now leads me to
think that I should hold back
my assent from opinions
which are not completely
certain and indubitable just as
carefully as I do from those
which are patently false. So,
for the purpose of rejecting all
my opinions, it will be enough
if I find in each of them at
least some reason for doubt.”
Possible doubt=uncertain.
Senses deceive.
Therefore, “knowledge” based
on sense experience is
rejected.
“How could it be denied
that these hands or this
whole body are mine?
“I see plainly that there
are never any sure
signs by means of
which being awake can
be distinguished from
being asleep.”
Anything I think I know
that is based on my
sensory experiences or
my experience of my
body is suspect.
I am not certain there
is a world “out there,”
and I am not certain I
have a body.
What’s left?
Trying Out the Skeptical Argument
Lemons are yellow.
The moon is much farther
away from me than the tops
of the trees are.
I am (X) years old.
American astronauts have
visited the moon.
I am now
reading this
PowerPoint
slide.
This room is
filled with light.
Mathematics
2+3=5
Or does it?
A deceiver implies a
deceived.
Doubt requires a doubter.
Thought requires a thinker.
There’s no world out there,
I have no body, and I can’t
trust my thoughts.
I think; I exist.
Ones’ essence—i.e. self—is
non-material (mind, soul).
The fundamental activity of
this self is thinking, doubting,
wondering, etc.
Life as a Brain in a Vat is Really Not Much of a Life
So how can Descartes
reclaim the world?
Must find God.
If there is an all-powerful,
all-knowing, all-good God,
then there the evil genius
cannot be calling all the
shots.
And God must be found in
a priori knowledge.
Some Questions
Does skepticism/doubt
promote tolerance or does it
give license to anti-social
behavior?
Is it possible to live our lives
without the psychological
comfort of certainty?
Assuming the skeptics are
right that genuine knowledge
is impossible, can they still
claim that some beliefs are
more worthy of being
embraced than others?
Is it better to live in ignorant
certainty or in thoughtful
doubt?
When does skepticism
become a cop out—that is,
an easy way to avoid
defending a claim?
To what degree should we
trust our senses?
Is skepticism livable?