PP111 Lecture 9 Notes
• Foundationalism is a theory of knowledge with a distinctive view about how our
beliefs can become justified.
• ‘All’ foundationalists hold:
o A) That knowledge rests on (ie. is derived from) a foundation of more
• Most foundationalists also hold:
o B) that basic beliefs must be known with complete certainty.
Descartes crack in the foundation makes for uncertainty
• Belief (opinion): To believe something is to have a conviction that it is true; but
beliefs can turn out to be false however strong our conviction is.
• Beliefs can be either true or false, but they can also be either justified or
• When a belief is justified then the person who holds the belief has reasons or
evidence for her belief.
• More precisely, a person is justified in holding a belief when she has reasons for
thinking that the belief is more likely to be true or false
• Justification comes in degrees (week, strong, conclusive).
• When a belief is not true, it does not constitute knowledge (it is a false opinion)
• Similarly, when a belief is not justified, it does not constitute knowledge ( it might
be for example only a lucky guess)
Knowledge and Belief
• We have knowledge when we have:
1. A belief (an opinion)
2. The belief is true;
3. We have conclusive (or at least very strong) justification for that belief
• Global Skepticism: We can have no knowledge about anything
• Local Skepticism: We can have no knowledge about some particular subject
• The usual grounds for scepticism:
o We cant arguire sufficient justification for our opinions.
The Sources of Ideas and of Knowledge (Two Views)
• Empiricism: (John Locke)
a. All ideas originate in experience;
b. Knowledge (justification) is based on sensory experience
• Rationalism: (Rene Descartes) a. At least some ideas are innate;
b. Knowledge (justification) is based on reason
• “When I considered the number of conflicting opinions touching a single matter
that may be upheld by learned men, while there can be but one true, I reckoned as
wellnigh false all that was only probable.” (9192)
• “I was thus led to infer that the ground of all our opinions is far more custom and
example than any certain knowledge.” (92)
o believed of what was knowledge was based on common sense instead of
something that we could say was certain
Descartes’ Model for Epistemology: The Geometric Method
• “The long chains of simple and easy reasonings by which geometers are
accustomed to reach conclusions… led me to imagine that all things, to the
knowledge of which man is competent, are mutually connected in the same way”
a. Begin with simple indisputable axioms;
b. Make careful deductions from the axioms;
c. Arrive gradually at knowledge of theorems of greater
1. Basic Beliefs: The axioms that are known with certainty.
a. Deductive Inference (in a valid deductive inference, the truth of the
premises guarantees the truth of the conclusion)
2. Non basic Beliefs: Justified by other beliefs (from which they are deducted);
these inherit the certainty of the beliefs from which they are deduced.
• Genuine ‘knowledge’ is limited to:
o Our basic beliefs
o Plus whatever we have correctly deducted from our basic beliefs. All
the rest is merely opinion.
o Everything that is known will be known with certainty
• Premiss 1: “All astronomers are inebriated”
• Premiss 2: “Alphonse is an astronomer.”
• Conclusion: “Alphonse is inebriated.”
o Definition: A valid argument is one in which it is not possible for the
conclusion to be false if the premises are all true
1. If Socrates was crushed by a steamroller, then he is dead.
2. Socrates is dead .
3. So, Socrates was crushed by a steamroller.
Why we need Basic Beliefs
1. Nothing can justify a belief except a belief.
a. Belief (#4) > Justified Belief (#3) > Justified Belief (#2) > Justified
2. A belief can only justify another belief if it is already justified. • From (1) & (2) An infinite regress of justification follows
o So, Either
A) we have an infinite number of justified beliefs
• But this is impossible
B) We have no beliefs
• But this is total scepticism
C) Some beliefs are self justifying
o If we have any knowledge at all, then we must have some selfjustifying
Descartes’ Quest for Certainty in Three Phrases
• Phrase One: Cleaning House (or tearing it down)
• “It is now some years since I detected how many were the false beliefs that I had
from my earliest youth admitted as true, and how doubtful was everything I had
constructed on this basis” (94)
• I must once for all seriously undertake to rid myself of all the opinions which I
formerly had known…
Descartes’ Method of Doubt
• “I ought to withheld my assent from matters which are not entirely certain and
indubitable. “ (94)
o Definition: A belief is CERTAIN when it is not possible that it is false
• “… if I am able to find in each one some reason to doubt this will suffice to
justify my rejecting the whole. “ (94)
o Methodological Skepticism: Reject every belief that is possible false,
however probable it is; everything left over will be certain
Initial Doubts: (a) The Unreliability of the Senses
• “… it is sometime proved to me that these senses are deceptive and it is wiser not
to trust entirely to anything by which we have once been deceived. “ (94)
• Limitations to doubts that are grounded in this way:
a. It is only relying on our senses that we can learn that our senses sometimes
b. This is no reason to think that our senses ever mislead us when the
perceptual conditions are optimal
More Radical Doubts:
• B) the Argument from Dreams
o “I remind myself that on many occasions I have in sleep been deceived
… I see so ma