Review: RationalismReview: Rationalism

• Parmenides the modelParmenides the model– Anti-experience—not a reason to believeAnti-experience—not a reason to believe– Leads to false conclusions—errorLeads to false conclusions—error

• No change (or motion)No change (or motion)– No talk of “is not” b/c doesn’t exist No talk of “is not” b/c doesn’t exist

• Like saying Like saying 無無也無無也– Becoming = ‘is not’ Becoming = ‘is not’ turns intoturns into ‘is’ ‘is’

• So illegitimateSo illegitimate

– Change is a thing’s not-being Change is a thing’s not-being its being its being• Predication blended with existencePredication blended with existence

Classical Chinese contrastClassical Chinese contrast

• Existence claim supportedExistence claim supported– Law of preservation of matterLaw of preservation of matter– Consistent with constant change (Consistent with constant change ( 陰陽 陰陽 yin-yang)yin-yang)– No ‘is’ verb--No ‘is’ verb-- 有 無有 無 you-wuyou-wu exist-notexistexist-notexist and and 也也

• Other Greek RationalistsOther Greek Rationalists– Zeno and motion paradoxesZeno and motion paradoxes– Pythagoras and concept of “proof”Pythagoras and concept of “proof”

• Mathematical mysticismMathematical mysticism

– Euclid: How to think—axioms + proof Euclid: How to think—axioms + proof all truth all truth• Role of definitions Role of definitions Socrates & ethics as theory Socrates & ethics as theory• Examined life = theory of the healthy soul=ethicsExamined life = theory of the healthy soul=ethics

Method of Good Thinking: Logic Method of Good Thinking: Logic

• Socratic MethodSocratic Method– DoubtDoubt——but much morebut much more– Rationally motivated doubtRationally motivated doubt

• Still in the same structureStill in the same structure——how proof motivates how proof motivates doubtdoubt

• Logic as disciplined discourseLogic as disciplined discourse– 'Argument': proof v quarrel sense'Argument': proof v quarrel sense– Proof consists of sentencesProof consists of sentences

• Premises and conclusionPremises and conclusion• Conversational implicationConversational implication

– Conclusion Conclusion ““follows fromfollows from”” the premises the premises– Needs explanationNeeds explanation

Good/bad arguments (proofs)Good/bad arguments (proofs)• Valid: has a Valid: has a formform such that if the premises such that if the premises werewere

true, the conclusion would also be truetrue, the conclusion would also be true• Formal-symbolic representationFormal-symbolic representation

– Venn diagram techniqueVenn diagram technique– Classic example: all C are B, all B are A, all C are AClassic example: all C are B, all B are A, all C are A

• AristotleAristotle’’s syllogisms syllogism——now propositional logicnow propositional logic

– Modes Ponens If Modes Ponens If ……thenthen……– Model Tolens &Disjunctive syllogismModel Tolens &Disjunctive syllogism

QuestionsQuestions

Quiz for New Years?Quiz for New Years?Formulate the problem of evil. Formulate the problem of evil.

Explain the advantage of a symbolic Explain the advantage of a symbolic statement. statement.

How to Prove How to Prove InInvalidityvalidity

• Use the same formUse the same form– With plainly true premisesWith plainly true premises

– And a false conclusionAnd a false conclusion

– Can not be a valid formCan not be a valid form

• Distinguish from argument Distinguish from argument byby analogy analogy– Form of induction on a similarityForm of induction on a similarity

– How do I know you have minds?How do I know you have minds?

SoundnessSoundness

• DefinitionDefinition– Valid argumentValid argument– True premises (all)True premises (all)

• Conclusion of two definitionsConclusion of two definitions– Sound arguments have true conclusionsSound arguments have true conclusions

• If an argument is valid and has true premises, then the If an argument is valid and has true premises, then the conclusion is true.conclusion is true.

• A sound argument is a valid argumentA sound argument is a valid argument• A sound argument has true premisesA sound argument has true premises• Therefore a sound argument has a true conclusionTherefore a sound argument has a true conclusion

• What if conclusion of valid form is falseWhat if conclusion of valid form is false– Contradiction of “all” is “one or some”Contradiction of “all” is “one or some”– At least one premise is falseAt least one premise is false

Other LogicsOther Logics• Deductive v inductiveDeductive v inductive

– Guarantee by form v good reason forGuarantee by form v good reason for• Could be wrong—reasonable conclusionCould be wrong—reasonable conclusion• Can’t use rule of the triad—conclusion false Can’t use rule of the triad—conclusion false

and still valid and premises trueand still valid and premises true

– Weakest to strongestWeakest to strongest• Analogy (weak form) one likenessAnalogy (weak form) one likeness• Classical induction: next one might changeClassical induction: next one might change• Sampling, polling and statistics (with rigor)Sampling, polling and statistics (with rigor)• Science (strong form) explain laterScience (strong form) explain later

– Inference to the best explanationInference to the best explanation

Moral Or Moral Or PracticalPractical Reasoning Reasoning

• Uses the same model: called the practical Uses the same model: called the practical syllogismsyllogism– Belief-desire explanation of action in western Belief-desire explanation of action in western

thoughtthought• Belief + desire (sentence) Belief + desire (sentence) entailentail intention/action intention/action• May substitute a norm/value/principle for May substitute a norm/value/principle for ““desiredesire””

– Desire the Desire the perceptionperception of value of value

• To get a value (ought) conclusion, you need To get a value (ought) conclusion, you need a value premisea value premise– You can't get an "ought" from an "is"You can't get an "ought" from an "is"– Abortion argument exampleAbortion argument example

Deduction and Method: Crucial MoveDeduction and Method: Crucial Move• If conclusion false, then either invalid or If conclusion false, then either invalid or

premise falsepremise false• Key to scientific induction (v. Classical Key to scientific induction (v. Classical

induction)induction)– Laws and experimental setup Laws and experimental setup predict predict a resulta result

• Premises are laws + observations/measurementsPremises are laws + observations/measurements• Conclusion is a prediction of experimental outcomeConclusion is a prediction of experimental outcome

– If prediction is false, one+ premise must be falseIf prediction is false, one+ premise must be false• Usually the setup, but after repeated checking calls Usually the setup, but after repeated checking calls

oneone of the laws into question of the laws into question • True True confirm (false confirm (false disconfirm) disconfirm)

Science: DetailScience: Detail• Premises and deductive conclusionPremises and deductive conclusion

– Laws: pure water freezes at 0 C.Laws: pure water freezes at 0 C.– This is waterThis is water– This is below 0 C.This is below 0 C.– This will freezeThis will freeze

• Doesn’t freeze—so?Doesn’t freeze—so?– Thermometer wrong, salt/alcohol mixed in water Thermometer wrong, salt/alcohol mixed in water

etc.etc.– If all ruled out—reject the lawIf all ruled out—reject the law

• Laws, measurements, mathematicsLaws, measurements, mathematics– Precision of prediction for sciencePrecision of prediction for science

Socratic ContradictionSocratic Contradiction

• Socratic method no experimentSocratic method no experiment– Use argument to derive a contradictionUse argument to derive a contradiction– Must change a premise. Not necessarily the Must change a premise. Not necessarily the

definitiondefinition– Limits of Socratic (scientific) method: only Limits of Socratic (scientific) method: only

exposes error not truthexposes error not truth– Trial and error, creativity, insight, genius for Trial and error, creativity, insight, genius for

premisespremises

Example: The Problem of EvilExample: The Problem of Evil

• God is omnipotent, omniscient and all good God is omnipotent, omniscient and all good creator of everythingcreator of everything– Hence, there is no evilHence, there is no evil

• Formal statement: AFormal statement: ABBCCD. All goodD. All good– "All things there are”"All things there are”– "things God made""things God made"– "things God wanted""things God wanted"– "good things“"good things“

• Evil = not good (definition)Evil = not good (definition)– There is no evil (everything is good/God’s will)There is no evil (everything is good/God’s will)

TheodicityTheodicity

• What is the alternative to no-evil?What is the alternative to no-evil?– God does not exist? Why does it not God does not exist? Why does it not

prove that?prove that?

– Theodicity: possible solutions to the Theodicity: possible solutions to the problem of evilproblem of evil• Limited godLimited god• Free will and necessary evilFree will and necessary evil• Human and divine “good”Human and divine “good”

Back to Socrates: Virtue Back to Socrates: Virtue

• Applies metaphysical analysis to ethics, Applies metaphysical analysis to ethics, truths are moral facts. truths are moral facts. – one (conventions many) one (conventions many) – unchanging (vs. mores) unchanging (vs. mores) – knowable (definitions) knowable (definitions) – rational (Socratic method) and rational (Socratic method) and – real. real.

• Why care about those peculiar facts? Why care about those peculiar facts? – No man knowingly does evilNo man knowingly does evil

Weakness of Socratic MethodWeakness of Socratic Method

• No answersNo answers——Socrates the skepticSocrates the skeptic– Dies ignorantDies ignorant– Famous lamentFamous lament——and student responseand student response

• At least knows he doesnAt least knows he doesn’’t knowt know• 知之為知之不知為不知是知也知之為知之不知為不知是知也

• Deeper problemDeeper problem——many different consistent many different consistent doctrinesdoctrines– Contradiction not easy to proveContradiction not easy to prove– Plato cheats!Plato cheats!

Socrates and Plato StorySocrates and Plato Story

• Death by legislatureDeath by legislature——bill of attainderbill of attainder– PlatoPlato’’s hatred of democracys hatred of democracy

• Better for policy and choice of leadersBetter for policy and choice of leaders• Not for judgment of guiltNot for judgment of guilt

• Takes Socrates as a figure in dialoguesTakes Socrates as a figure in dialogues– Source of our account of Socratic methodSource of our account of Socratic method– Classic example in Thrasymachus dialogueClassic example in Thrasymachus dialogue

Plato's Synthesis: Plato's Synthesis:

• Parmenides: the real world and ethical ideal Parmenides: the real world and ethical ideal blendblend

• Focus on search for definitionsFocus on search for definitions– Socrates origin or geometrySocrates origin or geometry

• Result is that meaning/value = beingResult is that meaning/value = being– Really that being = meaning/valueReally that being = meaning/value

Definitions: Definitions:

• Conform to rationalist presuppositionsConform to rationalist presuppositions– One -- instances are manyOne -- instances are many– Unchanging -- remain while that kind of thingUnchanging -- remain while that kind of thing– Knowable -- beliefs about objects (Heraclitus Knowable -- beliefs about objects (Heraclitus

and Parmenides)and Parmenides)– Rational -- Socratic methodRational -- Socratic method– Hence realHence real

• Idealism. Definitions (meanings:ideas) are realIdealism. Definitions (meanings:ideas) are real• "Things" are not"Things" are not

Rules for DefinitionsRules for Definitions

• Implicit in Plato's dialogues with SocratesImplicit in Plato's dialogues with Socrates• No lists. What is common to all instancesNo lists. What is common to all instances• No vagueness. StrongNo vagueness. Strong• No circularity (or mere synonyms) No circularity (or mere synonyms)

– Definition so usable in argumentsDefinition so usable in arguments

• No hearsay -- test by expert knowledgeNo hearsay -- test by expert knowledge– Real v. Nominal definitionsReal v. Nominal definitions

• Test by reason. Socratic methodTest by reason. Socratic method

Conclusion: The FormsConclusion: The Forms

• Intellectual forms correspond to definitions Intellectual forms correspond to definitions (meanings)(meanings)

• Forms provide a unified answer to questions in Forms provide a unified answer to questions in all fields of philosophyall fields of philosophy– Metaphysics: what is real. Real definitions v. NominalMetaphysics: what is real. Real definitions v. Nominal– Epistemology: what is knowable. Like soul/mind--Epistemology: what is knowable. Like soul/mind--

intellectualintellectual– Logic: the thinkable objects (not laws of thought but Logic: the thinkable objects (not laws of thought but

semantics)semantics)– Ethics: no man knowingly does evil. Health of the soulEthics: no man knowingly does evil. Health of the soul

• Objects of striving -- teleological account of changeObjects of striving -- teleological account of change