Transcript Review: Rationalism

Review: Rationalism
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Parmenides the model
– Anti-experience—not a reason to believe
– Leads to false conclusions—error
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No change (or motion)
– No talk of “is not” b/c doesn’t exist
• Like saying 無無也
– Becoming = ‘is not’ turns into ‘is’
• So illegitimate
– Change is a thing’s not-being  its being
• Predication blended with existence
Classical Chinese contrast
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Existence claim supported
– Law of preservation of matter
– Consistent with constant change (陰陽 yin-yang)
– No ‘is’ verb--有 無you-wu exist-notexist and 也
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Other Greek Rationalists
– Zeno and motion paradoxes
– Pythagoras and concept of “proof”
• Mathematical mysticism
– Euclid: How to think—axioms + proof  all truth
• Role of definitions  Socrates & ethics as theory
• Examined life = theory of the healthy soul=ethics
Method of Good Thinking: Logic
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Socratic Method
– Doubt—but much more
– Rationally motivated doubt
• Still in the same structure—how proof motivates doubt
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Logic as disciplined discourse
– 'Argument': proof v quarrel sense
– Proof consists of sentences
• Premises and conclusion
• Conversational implication
– Conclusion “follows from” the premises
– Needs explanation
Good/bad arguments (proofs)
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Valid: has a form such that if the premises
were true, the conclusion would also be true
Formal-symbolic representation
– Venn diagram technique
– Classic example: all C are B, all B are A, all C are A
• Aristotle’s syllogism—now propositional logic
– Modes Ponens If …then…
– Model Tolens &Disjunctive syllogism
Questions
Quiz for New Years?
Formulate the problem of evil.
Explain the advantage of a symbolic
statement.
How to Prove Invalidity
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Use the same form
– With plainly true premises
– And a false conclusion
– Can not be a valid form
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Distinguish from argument by analogy
– Form of induction on a similarity
– How do I know you have minds?
Soundness
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Definition
– Valid argument
– True premises (all)
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Conclusion of two definitions
– Sound arguments have true conclusions
• If an argument is valid and has true premises, then the
conclusion is true.
• A sound argument is a valid argument
• A sound argument has true premises
• Therefore a sound argument has a true conclusion
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What if conclusion of valid form is false
– Contradiction of “all” is “one or some”
– At least one premise is false
Other Logics
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Deductive v inductive
– Guarantee by form v good reason for
• Could be wrong—reasonable conclusion
• Can’t use rule of the triad—conclusion false
and still valid and premises true
– Weakest to strongest
• Analogy (weak form) one likeness
• Classical induction: next one might change
• Sampling, polling and statistics (with rigor)
• Science (strong form) explain later
– Inference to the best explanation
Moral Or Practical Reasoning
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Uses the same model: called the practical
syllogism
– Belief-desire explanation of action in western
thought
• Belief + desire (sentence) entail intention/action
• May substitute a norm/value/principle for “desire”
– Desire the perception of value
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To get a value (ought) conclusion, you need
a value premise
– You can't get an "ought" from an "is"
– Abortion argument example
Deduction and Method: Crucial Move
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If conclusion false, then either invalid or
premise false
Key to scientific induction (v. Classical
induction)
– Laws and experimental setup predict a result
• Premises are laws + observations/measurements
• Conclusion is a prediction of experimental outcome
– If prediction is false, one+ premise must be false
• Usually the setup, but after repeated checking calls
one of the laws into question
• True  confirm (false  disconfirm)
Science: Detail
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Premises and deductive conclusion
– Laws: pure water freezes at 0 C.
– This is water
– This is below 0 C.
– This will freeze
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Doesn’t freeze—so?
– Thermometer wrong, salt/alcohol mixed in water
etc.
– If all ruled out—reject the law
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Laws, measurements, mathematics
– Precision of prediction for science
Socratic Contradiction
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Socratic method no experiment
– Use argument to derive a contradiction
– Must change a premise. Not necessarily the
definition
– Limits of Socratic (scientific) method: only
exposes error not truth
– Trial and error, creativity, insight, genius for
premises
Example: The Problem of Evil
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God is omnipotent, omniscient and all good
creator of everything
– Hence, there is no evil
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Formal statement: ABCD. All good
– "All things there are”
– "things God made"
– "things God wanted"
– "good things“
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Evil = not good (definition)
– There is no evil (everything is good/God’s will)
Theodicity
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What is the alternative to no-evil?
– God does not exist? Why does it not
prove that?
– Theodicity: possible solutions to the
problem of evil
• Limited god
• Free will and necessary evil
• Human and divine “good”
Back to Socrates: Virtue
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Applies metaphysical analysis to ethics,
truths are moral facts.
– one (conventions many)
– unchanging (vs. mores)
– knowable (definitions)
– rational (Socratic method) and
– real.
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Why care about those peculiar facts?
– No man knowingly does evil
Weakness of Socratic Method
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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
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Deeper problem—many different consistent
doctrines
– Contradiction not easy to prove
– Plato cheats!
Socrates and Plato Story
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Death by legislature—bill of attainder
– Plato’s hatred of democracy
• Better for policy and choice of leaders
• Not for judgment of guilt
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Takes Socrates as a figure in dialogues
– Source of our account of Socratic method
– Classic example in Thrasymachus dialogue
Plato's Synthesis:
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Parmenides: the real world and ethical ideal
blend
Focus on search for definitions
– Socrates origin or geometry
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Result is that meaning/value = being
– Really that being = meaning/value
Definitions:
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Conform to rationalist presuppositions
– One -- instances are many
– Unchanging -- remain while that kind of thing
– Knowable -- beliefs about objects (Heraclitus
and Parmenides)
– Rational -- Socratic method
– Hence real
• Idealism. Definitions (meanings:ideas) are real
• "Things" are not
Rules for Definitions
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Implicit in Plato's dialogues with Socrates
No lists. What is common to all instances
No vagueness. Strong
No circularity (or mere synonyms)
– Definition so usable in arguments
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No hearsay -- test by expert knowledge
– Real v. Nominal definitions
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Test by reason. Socratic method
Conclusion: The Forms
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Intellectual forms correspond to definitions
(meanings)
Forms provide a unified answer to questions
in all fields of philosophy
– Metaphysics: what is real. Real definitions v.
Nominal
– Epistemology: what is knowable. Like soul/mind-intellectual
– Logic: the thinkable objects (not laws of thought but
semantics)
– Ethics: no man knowingly does evil. Health of the
soul