REVIEW LOGIC & REASONING

Deductive Validity—formal

A form such that true premises always  true
conclusions


Informal test—imagine an argument in that form
 Core vocabulary: if..then.., and, or, not, all, some, none
 True premises & false conclusion
Sound = df valid and all true premises

“Conclusions of sound deductive arguments are true”

Sound deduction from definition premises
OTHER LOGICS
 Inductive—valid
when good reasons for
the conclusion


Not a guarantee
Analogy, induction on example(s), sampling,
science

Inference to the best explanation
 Practical
syllogism: belief-desire to
intention

Needs an “ought” in premises
INCONSISTENT TRIAD (DEDUCTIVE)

If conclusion false then


Either premise(s) false or invalid
Formal test for validity
Then key to Socratic rational doubt
 Doubt one of your premises


Also key to science: hypothetical decuction

Take current theory as hypotheses


Measurements, mathematics
Predict experimental outcome

Outcome falsifiessome hypothesis wrong
SOCRATES AND RELIGION APPLICATION

Socrates no experimental method

Needs explicit contradiction—harder


Limits: reveals error not truth


Plato cheats a lot
No method to discover truth
Problem of Evil even looser
Needs formal statement unlike the usual
 Believer has many options

Accept evil
 Best of all possible worlds: Free will
 Limited God
 Not creator

THEODICY
 What

God does not exist?


is the alternative to no-evil?
Why does it not prove that?
Theodicy: possible solutions to the
problem of evil
Limited god (not perfect/omnipotent)
 Free will and necessary evil


Necessary for greater good
Human and divine “good”
 Or accept the conclusion


Evil is an illusion
Tutorials sign up
Start next week
2 quizzes
QUESTIONS?
BACK TO SOCRATES: VIRTUE
 Use

metaphysics model on ethics
Fundamental reality of ‘virtue’, ‘justice’

Search for definitions using Socratic method
one (conventions many)
 unchanging (vs. mores)
 knowable (definitions)
 rational (Socratic method) and
 Real (!)

 Why

care about those peculiar facts?
No man knowingly does evil
WEAKNESS OF SOCRATIC METHOD
 No
answers—Socrates the skeptic
Dies ignorant
 Famous lament—and student
response

At least knows he doesn’t know
 知之為知之不知為不知是知也

 Deeper

problem
Many different consistent doctrines
Contradiction not easy to prove
 Plato the playwright takes control

SOCRATES AND PLATO STORY
 Death

by legislature—wrong
Plato’s hatred of democracy
Better for policy and choice of leaders
 Not for judgment of guilt


separate judiciary rule of law
 Socrates
as figure in his dialogues
Development of Socratic method
 Classic example in Thrasymachus
dialogue

PLATO'S SYNTHESIS:

Parmenides: the real world and ethical ideal
blend


Real is rational; rational is real
Focus on search for definitions
Socrates origin and geometry
 The idea or concept of a thing


Result is the meaning/value = being

Really that being = meaning


Meaning linked to value, purpose
The concept is the thing’s “reality”
ARE DEFINITIONS IMPORTANT?
Not
to knowing how to speak
Vicious
circle
Real life and children learning
Examples: true, cute, way, water
Why
such emphasis?
Importance

Socratic method and validity
Problem

to logical method
of evil example
Can’t test validity w/o form
DEFINITIONS: CONCEPT REALITY
Conform
to rationalist
presuppositions
 One
– concrete instances are many
 Unchanging – remain; things change
 Knowable -- beliefs about objects

Heraclitus and Parmenides
 Rational
-- Socratic method
 Hence real

Idealism
Definitions (meanings:ideas) real
 Sensible “things" are not

RULES FOR DEFINITIONS
Implicit in Plato's Socrates
 No lists. What is common to all
instances
 No vagueness. ‘Strong’?
 No circularity (or mere synonyms)

Definition so usable in arguments
 No

hearsay -- test by expert knowledge
Real v. Nominal definitions
 Test
by reason. Socratic method
CONCLUSION: THE FORMS
 Forms

correspond to definitions (meanings)
Meaning “objects”
 Provide

Metaphysics: what is real—objective meaning


Like soul/mind--intellectual
Logic: the thinkable objects


Real definitions v. Nominal
Epistemology: what is knowable


unified answer to philo questions
Not laws of thought but semantics
Ethics: no man knowingly does evil
Health of the soul
 Definitions of virtues
 Objects of striving -- teleological account of change

DIFFICULTY: FAMOUS ANALOGIES
 Cave:


sensible appearance v reality
C.f. taking hallucinatory drugs
Meditation or rational insight
 Analogy:
shadow/object as
object/form
Equal difficulty in getting you to
accept them
 When you "see" them, you will need
no more convincing


The character of the object determines
your knowledge
LINE ANALOGY:
Links
metaphysics and
epistemology
Knowability depends on nature
of object (Parmenides)
Rival view: true belief plus an
account (the modern analysis)
X
knows that P =df.
P is true
X believes that P
X has justification for believing that P

THE SUN ANALOGY
Rule
for identification of forms
 Logic:
there must be a form of
forms
 It must be “more real” than the
forms
The
form of the good: of all value
Form of the truth/beauty/good
MYSTICAL RESULT
Absolute
one/being
No reason leading to see it
It would blind us
But necessarily there (or
nothing exists)
KEY POLITICAL DOCTRINES
The
Republic a political
plan
 Justice
of political structure
like that of individual
Same in everything
Rule of the correct ruler—
intellect

THE PHILOSOPHER KING
Anti-democratic
and
manipulative
Education and classes
Social ranks: intellectual,
spirited, body-like
END OF PLATO AND GREEK RATIONALISM

Ancient Chinese idealism next!