批判性推理入門criticalreasoningforbeginners全筆記

1、Critical Reasoning for beginnersby Marianne Talbot OxfordLesson 1 How to recognize arguments and What is the nature of argumentsArguments are a set of sentences such that one of them (the conclusion) is being said to be true, and the other(s) (the premises) are being offered as reasons for believing

2、 the truth of the one.An argument isn't a set of contradictions.Part of the point of an argument is to move us on from where we are to somewhere a bit further.Arguments lead to deeper thoughts. (from where we are to where we want)An Argument:(one or more) Premises 1 Conclusion(Function)to prove-

3、reasons suppose true relationship among sentences.It's Friday.Marianne always wears jeans on Friday.Therefore Marianne will wear jeans today.Play attention to suppressed premises(隱藏前提)contextall sentences may be argument.implication(實(shí)質(zhì)蘊(yùn)涵)entailment (邏輯蘊(yùn)涵)Distinguish arguments from(a) sets of sen

4、tences not related as arguments(1) aren't related at all .The sea is salt.Sydney is in Australia.(2) related but not an argument.Towards lunchtime clouds formed and the sky blackened. Then the stormbroke.(b) sentences (assertions) 'if.then.' .If it is snowing, the mail will be late. (imp

5、lication not entailment)An argument is a set of sentences, one of which is being asserted.An assertion is a single sentence (possibly complex) ,that is being expressed in assertive mode.'because' may be causal or rational.reason and causecausal relations(因果關(guān)系)and rational relations (推理關(guān)系)A a

6、nd B entail C doesn't mean A and B cause C.It's Friday. (A)Marianne always wears jeans on Friday. (B)Therefore Marianne will wear jeans today. (C)explanation:(1) causal explanation (因果性解釋)： .Pawl fell down because he wanted to amuse children.(2) rational explanation(推理性解釋)：.Pawl fell down be

7、cause Jelly pushed him.Facts are what makes sentences true or false. They are not true or false, they just exist or don't exist.Only beliefs or sentences that express beliefs are true or false.Belief . concept)the concept 'chair'Languagethe language 'c-h-a-i-r'Realitythe object &

8、#39;chair'Arguments can only be good or bad ,they can only be valid or invalid ,they can't be true or false because the only thing that can be true or false is beliefs or the sentences that express beliefs.A good argument is one in which:(1)the conclusion must follow the premises(3) the prem

9、ises must all be true .The conclusion must be true. (truth preserving)邏輯學(xué)并不關(guān)心前提正確與否，而只關(guān)心前提與結(jié)論的關(guān)系Lesson 2 Different sorts of argumentstwo basic types of arguments: deduction and inductionDeductive argument :the truth of their premises guarantees the truth of their conclusion.It's Friday.Marianne

10、always wears jeans on Friday.Therefore Marianne will wear jeans today.If the premises are true, the conclusion would be true.'truth guaranteeing' 'truth preserving'Deduction is an 'either or' thing:a good deductive argument gives us conditional certainty.a bad one tells us no

11、thing.conclusioncontents.Inductive arguments are such that the truth of their premises makesthe more or less probable. (don't guarantee)Inductive arguments can be either weak or strong.strong:The sun has risen every day in the history of the universe. Therefore the sun will rise tomorrow.weak:Ev

12、ery time I met Mary, she wore a necklace.Therefore the next time I meet her, she will wear a necklace.邏輯學(xué)是中立性的，邏輯的形式可以適用于任何的內(nèi)容。Logicians study deduction by studying valid arguments formsArguments that are valid is in virtue of their forms as opposed to theirthe forms of deduction:1、Modus Ponens肯定前件取

13、拒式If P then Q, P, therefore Q. (P,Q sentences)wrong: If P then Q, Q, therefore P.(Affirming consequent 肯定后件式)2、Modus tollens 否定后件式If P then Q, not-Q, therefore not-P.3、Disjunctive syllogism選言三段論P(yáng) or Q, not-P, therefore Q.(P或Q成立，P不成立，因此Q成立)4、Leibniz's Law萊布尼茲律(相同者不可辨識)a is F, a=b, therefore b is

14、F. Jane is(predication) tall.Jane is(identity) the bank manager.Therefore the bank manager is(predication) tall.Note:'is' can serve as a predication (論斷) or identity (同等).The 'is's above serve as predications.And the '=' above serves as identity.5、Syllogism 三段論 all Fs are G.a

15、 is an F.Therefore a is a G.6、Deontic Logic 道義邏輯. Lying is wrong.Therefore we shouldn't lie.7、Modal Logic 模態(tài)邏輯(a logic about necessity and possibility).It is necessarily the case that there are no square circles.Therefore it is not possible that there are square circles.8、Temporal Logic時(shí)序邏輯(時(shí)態(tài)邏輯

16、).It is raining today.Therefore tomorrow it will have been raining yesterday.Inductive argumentsAll inductive arguments rely on the assumption of the uniformity of nature (the idea that the future will be like the past)哲學(xué)中的一個(gè)基本問題是，我們對未來的假設(shè)，會不會和過去的經(jīng)驗(yàn)相一致Uniformity一致性，uniformity of nature (David Hume)自

17、然界是否具有一致性Within the category of inductive arguments there are many different sub-types:1、 arguments from analogy 類比推理a is like b, a is F, therefore b is F.(小寫字母：particular thing 特定的事物大寫字母：性質(zhì)或句子)2、 arguments from authority訴諸權(quán)威的論證. Einstein is a brilliant physicist.Einstein says relativism is true.The

18、refore relativism is true.Causal arguments 因果論證Causal arguments can be deductive or inductive , depending on whether we are arguing from a causal claim or to a causal claim.deductive: As cause Bs.There was an A.Therefore there will have been a B.inductive: Every observed A has been followed by a B.T

19、herefore As cause Bs.negative existential 否定存在判斷句 .飛馬不存在。We can know thatarguments that are deductively validin virtue of their formsin virtue of their content.Deontic Logic ,Temporal Logic arguments that are inductively valid the uniformity of natureLesson 3 'logic-book-style' 邏輯書the point:

20、(a)it enables us to add suppressed premises隱含前提(b)it enables us to eliminate cross references, irrelevancies and inconsistent terms排除交叉引用、無關(guān)和不一致詞語(c)it makes it easier to evaluate arguments.A set of steps for analyzing arguments:1. identify the conclusion of the argumentLook for the argument indicat

21、ors (so, therefore, then, if.then., accordingly, hence, since, for, because, from which we see that, it follows that, which establishes that.) 2. identify each of the premises 3. add suppressed premises 4. remove irrelevancies 5. remove inconsistent terms 6. remove cross-referencesExample 1:Socialis

22、m did not provide the incentives need for a prosperous economy. Therefore socialism was doomed to failure.Premise 1: Incentives are needed for a prosperous economy.Premise 2: Socialism did not provide incentives. Conclusion: Socialism was doomed to failure.Premises and conclusion must be sentences.P

23、, unless Q.If Q, then R. P1kBut not R.Example 2:Since many newly emerging nations do not have the capital resources necessary for sustained growth, they will continue to need help from industrial nations.Premise 1: Many newly emerging nations do not have capital resources Premise 2: Capital resource

24、s are necessary for sustained growth.Premise 3: If a newly emerging nation is to sustain its growth, and it does not have capital resources, it will need help from industrial nations.Conclusion: Many newly emerging nations will need help from industrial nations.Example 3:Well perhaps she didn't

25、want you to tickle her tummy, or she didn't realize that was what you were going to do. If she didn't realize , then you obviously went about it in the wrong way. In that case you deserved to get scratched unless you ready thought she was such a perceptive cat that she'd understand '

26、woof-woof'meant 'roll over '. If you thought that you're an idiot. But you're not an idiot you're just twisted. So if the poor thing did want you to tickle her tummy you deserve to get scratched.1 Identify premises and conclusionPremise1: Well perhaps she didn't want you

27、to tickle her tummy, or she didn'trealize that was what you were going to doPremise2: If she didn't realize , then you obviously went about it in the wrong way.Premise3: In that case you deserved to get scratched unless you ready thoughtshe was such a perceptive cat that she'd understand

28、 'woof-woof meant 'roll over '.Premise4: If you thought that , you're an idiot. But you're not an idiot you're just twisted.Conclusion: So if the poor thing did want you to tickle her tummy you deserve to get scratched.2 Add suppressed premises(None)3 Remove irrelevanciesdraf

29、t:Premise1: Well perhaps she didn't want you to tickle hertummy or she didn'trealize that was what you were going to doPremise2: If she didn't realize , then youobviously went about it in the wrongway.Premise3: In that case you deserved to get scratchedunless you ready thoughtshe was suc

30、h a perceptive cat that she'd understand 'woof-woof meant 'roll over.Premise4: If you thought that , you're an idiot. But you're not an idiot you're just twisted.Conclusion: So if the poor thing did want you to tickle hertummyyou deserveto get scratched.Premise1: She didn'

31、;t want you to tickle her, or she didn't realize that was what you were going to doPremise2: If she didn't realize , then you went about it in the wrong way.Premise3: In that case you deserved to get scratched.Conclusion: So if the poor thing did want you to tickle her you deserve to get scr

32、atched.4 Remove inconsistent terms and cross references (simplify)Premise1: She didn't want you to tickle her, or she didn't realize you were going to tickle herPremise2: If she didn't realize you were going to tickle her , then you were going to tickle her in the wrong way.Premise3: If

33、you were going to tickle her in the wrong way, you deserved to getscratched.Conclusion: So if she did want you to tickle her, you deserve to get scratched.To show you how easy it is to reveal the structure of this argument , let's formalize it.Premise1: She didn't want you to tickle her, or

34、she didn't realize you were going to tickle herPremise2: If she didn't realize you were going to tickle her , then you were going to tickle her in the wrong way.Premise3: If you were going to tickle her in the wrong way, you deserved to get scratched.Conclusion: So if she did want you to tic

35、kle her, you deserve to get erpreter:'she didn't want you to tickle her' is P.'she didn't realize you were going to tickle her' is Q.'you were going to tickle her in the wrong way' is R.'you deserved to get scratched' is S.Premise1: P or Q.Premise

36、2: if Q then R.Premise3: if R then S.Conclusion: if not-P then S.Note: you can apply this methodology to your own argument, this will help you understand exactly what you are saying and why you are saying it.Wesaw that although we need to paraphrase arguments in order to complete these steps, we sho

37、uld not change the meaning of any of the premisesor the conclusion.Lesson 4 How to evaluate whether an argument is a good one or a bad oneAll inductive arguments rely on the principle of the uniformity of nature and the only arguments for the principle of the uniformity of nature are themselves indu

38、ctive.Types of inductive argument:inductive generalizations歸納性的概括causal generalizations 偶然的概括 arguments from analogy從類推得至U的論點(diǎn) arguments from authority 從權(quán)威得至U的論點(diǎn)Inductive generalizationsThe premises identifies a characteristic of a sample of a population and the conclusion extrapolates that character

39、istic to the rest of the population.Evaluating inductive generalizations the premises true large is the sample representative is the sample 'informal' heuristics當(dāng)心非正式的啟發(fā)式方法 a way of making a decisionthere a counterexample 反例Causal generalizationsThe premise identifies a correlation between t

40、wo types of event, the conclusion states that the events of the first type cause events of second type.Evaluating causal generalizations因果歸納the premise trueAll we ever see is correlation（本目互關(guān)系）.Wenever see the causal relationshipitself.strong is the correlation（sample）the causal relation make sense

41、（有意義） or could it be accidental cause what there a counterexample 反例休謨認(rèn)為，All we see are correlation, we never see and get to the causal relationship itself更進(jìn)一步認(rèn)為因果關(guān)系實(shí)際上根本不存在，只是人的習(xí)慣性思維。Arguments from analogyArguments from analogy take just one example of something and extrapolate from a character of

42、that example to the character of something similar to that thing.Evaluating arguments from analogy the two things similar they similar in respect of（關(guān)于、涉及） something relevantwe find a Disanalogy （不相似點(diǎn)-相似并非等同）Arguments from authorityArguments from authority take one person or group of persons who are

43、, or are assumedto be ,right about something and extrapolate to the claim they are right about other thing.Evaluating arguments from authority exactly is the source of information this source qualified in the appropriate area this source impartial（公平公正的）in respect of this claimother experts make oth

44、er claimLesson 5 Validity vs. Truth （deductive argument）A good deductive argument is SOUND （可靠的）if and only if it:（a） is valid（b） has true premisesSound = valid argument + True premisesThere are many ways in which we determine the truth or falsehood of premises and these ways do not fall into the sc

45、ope of a class on critical reasoning.Validity, on the other hand is very muchof interest to logicians because validity preserves truth.We often don't know the truth of our premises and we often test the truth of our premises by constructing valid arguments and testing the truth of the conclusion

46、 . If we can show that the conclusion of a valid argument is false what do we therebydiscover At least one premise is false.Hypothesis: Smoking causes cancer.Prediction： If smoking causes cancer, then every smoker will get cancer.Test: Each smoker gets cancer.valid argumentTest（conclusion） is false.

47、 Prediction or Hypothesis（premise） is false.Testing of scientific hypothesis:Here is the best theory that philosophers and mathematicians can come up with: arguments is valid if and only if there is no possible situation in which all | | its premises are true and its conclusion false.An argument is

48、valid if and only if（當(dāng)且僅當(dāng)）there is no possible situationin which all its premises are true and its conclusion is false.Possibility not Actuality validtruth preserving2+2=5.Therefore grass is green. valid-based on definition（前提永彳段）Grass is green.Therefore 2+2=4. valid （結(jié)論永真）paradox （悖論）矛盾可以推出任何結(jié)論。Tru

49、e premisesFalse premisesTrue conclusionPossibly validinvalidFalse conclusionPossibly validPossibly validVenn diagrams （韋恩圖）to determine arguments validity. Possible truth valuesmatterPremises actually true and conclusion actually trueValid argumentInvalid argumentAll cat meow.Po does not meow.All ca

50、t meow.Dogs are not cats.Po is not a cat.Dogs don't meow.Premises actually false and conclusion actually trueValid argumentInvalid argumentAll fish have lungs Whales are fish.All fish have scales.Whales have scales.Whales have lungs.Whales are not fish.Premises actually false and conclusion actu

51、ally falseValid argumentInvalid argumentAll fish have wings.Whales are fish.All fish have scales.Whales have scales.Whales have wings.Whales are fish.Another way to determine validity is to create a counterexample set and determine consistencyIf the counterexample set is consistent then the original

52、 argument is invalid.如果反例集合可能同時(shí)為真，則原論證為無效的。I f the counterexample set isn ' t consistent then the original argument is valid.如果反例集合不可能同時(shí)為真，則原論證為有效的。.If it is snowing the mail will be late.The mail will be late.Therefore it is not the case （并三F）it is snowing.If it is snowing the mail will be late

53、.It is snowing.Therefore it is not the case the mail will be late.Lesson 6 Common fallaciesA FALLACY is an argument that looks like a good argument but which is not a good argument.In particular we are going to look at fallacies of:of relevance（關(guān)聯(lián)）（a）citing in support of a conclusion something that

54、is true but irrelevantNon- SequiturBill lives in a large building, therefore his apartment is large.Every year many people are supported through life by their religious beliefs, so their religious beliefs must be true.Reason for working:These arguments work because people don ' t notice the irre

55、levance, and because they are overly: a) generous (they are reluctant to point out the irrelevance);b) proud (they don ' t want to admit they can ' t see a connection)principle of charity:Arguing is life blood of cooperating and searching the truth. If you want know the truth, you cooperate

56、with other rational animals. If you find the contradiction, don ' t assume other person is wrong, the only rational thing to assume is one of you is wrong. Even that might be false.(b)Attacking the person making the argument rather than the argument that is made .Nick Griffin is leader of the BN

57、P, therefore his claim that some people worry about immigration is rubbish.Von Daniken's books about ancient astronauts are worthless because he is a convicted forger and embezzler.Be careful to distinguish ad hominem attack s: attacks on someone ' s right to say Something. -OK ad hominem fa

58、llacies: attacks on the truth of what someone Says - Not OK .An ad hominem attack:Nick Griffin is a self-professed racist, so you should take care when listening to his claims about immigration.An ad hominem fallacy: Nick Griffin is leader of the BNPtherefore his claim that somepeople worry about immigration is rubbish.of vacuity(空虛)(a)citing in support of a conclusion that very conclusion (circular arguments) .All whales are mammals, therefore all whales are mammals.In a circular argument the conclusion IS one of the p