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What We’ll Cover in Unit 8
I. The Nature of Knowledge
A. What is a theory of knowledge?
B. Plato on Knowledge
1. Theaetetus’ Theory of Knowledge
2. Socrates’ Refutation of Theaetetus
3. Plato’s Theory of Knowledge
C. Gettier’s Refutation of Plato
II. Hume’s Problem of Induction
The Three Fundamental Questions of Philosophy
1. What is there?
2. What should I do?
3. How can I know?
(Metaphysics)
(Ethics)
(Epistemology)
Some Questions in Epistemology
1. What is knowledge?
2. What is epistemic justification?
3. What are the fundamental sources of knowledge?
4. What are the limits of human knowledge?
5. What is the status of skepticism?
The Nature of Knowledge
Our First Question: What Is Knowledge?
• Putting the question this way makes the question sound really hard. Here are two other ways to put it:– “What is it to know something?”– “Under what conditions is it true that a person
qualifies as knowing that something is the case?”
• An answer to this question will be a theory of knowledge.
What is a theory of knowledge?
A theory of knowledge is a statement of the conditions under which a person knows that something is the case.
It is a statement of this form:
S knows that p if and only if ____S____p____ .
Theories are knowledge are supposed to reveal the
nature of knowledge.
Further Clarification of the Question ‘What is Knowledge?’Three Ways the Word ‘Knows’ Is Used:
• “Bob knows how to ride a bicycle.”
• “Bob knows the president of the U.S.”
• “Bob knows that the earth is round.”
The theories of knowledge we’re looking at are about the third kind of knowledge – called knowledge that, or propositional knowledge.
How Do We Go About Constructing (and Evaluating)
a Theory of Knowledge?Analogy: Bachelorhood.What is bachelorhood?What is it to be a bachelor?What are the conditions under which a person qualifies as a bachelor?What a “theory of bachelorhood” looks like: x is a bachelor if and only if _____x_____.
The Socratic Method, or the Method of Counterexamples
• A generalization is proposed• We try to come up with a “counterexample”
to it – i.e., a concrete example that “counters”, or shows false, the generalization just proposed
• If we do, we have refuted the generalization (but we might use the counterexample to help us improve on the generalization just refuted)
• If we can’t, perhaps the generalization is true.
What We’ll Cover in Unit 3
I. The Nature of Knowledge
A. What is a theory of knowledge?
B. Plato on Knowledge
1. Theaetetus’ Theory of Knowledge
2. Socrates’ Refutation of Theaetetus
3. Plato’s Theory of Knowledge
C. Gettier’s Refutation of Plato
II. Hume’s Problem of Induction
Plato on Knowledge
Plato (428-347 BC)
• The best known ancient Greek philosopher
• Student of Socrates; teacher of Aristotle• Wrote about 23 philosophical dialogues• Famous doctrine: the Theory of the
Forms• Western philosophy “consists of a
series of footnotes to Plato.” - A. N. Whitehead (1929)
excerpt from the
Theaetetus
by
Plato
translated by F.M. Cornford
Socrates: Well, that is precisely what I am puzzled about. I cannot make out to my own satisfaction what knowledge is. Can we answer that question. What do you think?
Socrates: But the question you were asked, Theaetetus, was not, what are the objects of knowledge, nor yet now many sorts of knowledge there are. We did not want to count them, but to find out what the thing itself – knowledge – is. Is there nothing to that?
Theaetetus: No, you are quite right. …
Socrates: Then tell me, what definition can we give with the least risk of contradicting ourselves?
Theaetetus: The one we tried before, Socrates. I have nothing else to suggest.
Socrates: What was that?
Theaetetus: That true belief is knowledge. Surely there can at least be no mistake in believing what is true and the consequences are always satisfactory.
Theaetetus’ Theory of Knowledge
The True Belief Theory:
S knows that p if and only if
(i) S believes that p; and
(ii) p is true.
Socrates’ Argument Againstthe True Belief Theory
Soc: You will find a whole profession to prove that true belief is not knowledge. …
The profession of those paragons of intellect known as orators and lawyers. There you have men who use their skill to produce conviction, not by instruction, but by making people believe whatever they want them to believe. You can hardly imagine teachers so clever as to be able, in the short time allowed by the clock, to instruct their hearers thoroughly in the true facts of a case of robbery or other violence which those hearers had not witnessed. …
… when a jury is rightly convinced of facts which can be known only by an eyewitness, then, judging by hearsay and accepting a true belief, they are judging without knowledge, although, if they find the right verdict, their conviction is correct? …
But if true belief and knowledge were the same thing, the best of jurymen could never have a correct belief without knowledge. It now appears that they must be different things.
Socrates’ Argument Against The True Belief Theory
The Argument
1. If the True Belief Theory is true, then the jury knows that I committed the crime.
2. But they don’t know I committed the crime.
3. Therefore, the True Belief Theory is not true.
Further Counterexamples to the True Belief Theory of Knowledge:
a. My belief that our football team will win their next game.b. Groundhog’s Day example.
Each case shows that true belief is not sufficient for knowledge.
The Lesson:
a belief that is truejust because of luck does not
qualify as knowledge.
Plato’s Theory of Knowledge
Socrates: So when a man gets a hold of the true notion of something without an account, his mind does think truly of it, but he does not know it, for if one cannot give and receive an account of a thing, one has no knowledge of that thing. But when he also has got hold of an account, all this becomes possible to him and he is fully equipped with knowledge. … a true notion with the addition of an account is knowledge?
Plato’s Theory of Knowledge
The JTB Theory
S knows that p if and only if
(i) S believes that p;
(ii) p is true; and
(iii) S is justified in believing that p.
Comments About the JTB Theory
a. How it avoids the counterexamples to the True Belief Theory
b. Theory of Justification still needed.
c. Some possible ways to be justified in believing something:
i. perception iv. testimony
ii. introspection v. induction
iii. memory vi. deduction
d. Theory accepted for thousands of years.
e. Theory no longer accepted today.
What We’ll Cover in Unit 3
I. The Nature of Knowledge
A. What is a theory of knowledge?
B. Plato on Knowledge
1. Theaetetus’ Theory of Knowledge
2. Socrates’ Refutation of Theaetetus
3. Plato’s Theory of Knowledge
C. Gettier’s Refutation of Plato
II. The Problem of Induction
Gettier’s Refutation of Plato
Edmund Gettier (1927- )
• Not the best known contemporary American philosopher, but pretty well know.
• Student of his teachers at Cornell; teacher of me at UMass.
• Wrote just one 3-page paper.• Famous doctrine: Justified true belief ain’t
knowledge.• A. N. Whitehead (1929) probably didn’t say
anything about Gettier.• Really good at badminton.
A Gettier-style Counterexample
• STEP 1. Suppose I see your driver’s license, an Alaska driver’s license.
This seems to justify me in believing
(1) You are from Alaska.
Note: this assumes that justification does not entail truth.
(That is, that what justifies me in believing something need not absolutely guarantee that that thing is true.)
A Gettier-style Counterexample• STEP 2. Now suppose that on the basis of
my belief that (1) You are from Alaska I come to believe that (2) Someone in my class is from Alaska. It seems that I am justified in believing (2). This is due to the following principle: If S is justified in believing p, and p entails q,
and S believes q on the basis of S’s belief that p, then S is justified in believing q.
A Gettier-style Counterexample• STEP 3. Now suppose that the driver’s
license I saw was in fact a fake ID, and that
(1) You are from Alaska
is in fact false.
(Note: I have a false justified belief in (1).)
(Note also: the JTB Theory thus far implies, correctly, that I do not know (1).)
A Gettier-style Counterexample• STEP 4. Finally, suppose that, just by
chance, someone else in the class really is from Alaska.
In other words, my belief that (2) Someone in my class is from Alaska actually turns out to be true.
It is true just by luck.
A Gettier-style Counterexample• STEP 5. Let’s ask some questions about
this proposition: (2) Someone in my class is from Alaska.• FIRST QUESTION: Would you say that I
know (2)? ANSWER: No.• SECOND SET OF QUESTIONS:
Is (2) true? YESDo I believe (2)? YESAm I justified in believing (2)? YES
A Gettier-style Counterexample• STEP 6: Thus, bringing it all together: I have a justified true belief in (2), but I don’t
know (2).
In the form of a little argument …
A Gettier-style Argument Against JTB:1. If the JTB Theory is true, then I know that
someone in our class is from Alaska.2. But it’s not true that I know that someone in
our class is from Alaska.3. Therefore, the JTB Theory is not true.
Other Gettier-style Examples
• The Hallucination
• Russell’s Clock
• The Sheep in the Field
A Way to Save the JTB Theory
• Note that what all the examples have in common: the subject has highly reliable, but not infallible, evidence for the proposition believed.
• To say that e is infallible evidence for p is to say that e entails p.
• Recall that Gettier’s argument assumed that a person can be justified in believing something without having infallible evidence for it.
A Way to Save the JTB Theory
• But consider this thesis about justification:
Infallibilism: S is justified in believing p only if S’s evidence for p entails p.
• If Infallibilism is true, then Gettier’s argument against JTB fails.
• But is Infallibilism true? …
