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by: Gianni Kunde


Gianni Kunde
GPA 3.55

C. Blakley

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C. Blakley
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This 30 page Class Notes was uploaded by Gianni Kunde on Tuesday October 13, 2015. The Class Notes belongs to PHIL 1000 at Louisiana State University taught by C. Blakley in Fall. Since its upload, it has received 9 views. For similar materials see /class/223074/phil-1000-louisiana-state-university in PHIL-Philosophy at Louisiana State University.

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Date Created: 10/13/15
Neeitlelpl 2011 Spring PHIL 1000 Section 001 for Christopher Blakley 39 39 I Jump to You are here W gt 201lsprlngPHIL100035701 I V Resoumes gt Is Philosophy Subjective Notes This resource should appear in a popup window If it didn39t click here 39 39 39 7 You are logged in as AM LQQQUI W fileCConverterInputBXGKTgV4vzhtm5122011 104048 PM Needeelpl 2011 Spring PHIL 1000 Section 001 for Christopher Blakley 39 39 I Jump to You are here MLCoutses gt 201lsprlngPHIL100035701 V RQSDJJLQQS gt Critical Thinking Notes This resource should appear in a popup window If it didn39t click here You are logged in as AM LQQQUI W fileCConverterInputDSSJDL6yDKhtm5122011 104050 PM 11810 Philosophy Critical Thinking amp Logic Philosophy Critical Thinking amp Logic This presentation covers some basic principles of critical thinking Wi gggimm 6ND informal fallacies and basic logic Philosophy Critical Thinking amp Logic Philosophy inquiry and analysis takes its point of departure from the refusal of dogmatism sophistry willful ignorance and intellectual dishonesty It s committed to examining all the relevant information questioning received opinion overcoming bias and following the evidence and arguments to the conclusions to which they logically lead whether it makes us happy or not Philosophy Critical Thinking amp Logic Textbook Definition of Philosophy quotAttempting to discern and remove contradictions among nonempirical reasoned beliefs that have universal importance with the resulting benefit of achieving a greater understanding of the world and our place within it Classic Questions p 5 Philosophy Critical Thinking amp Logic In his book On Bullshit Harry Frankfurt describes another attitude towards argumentation the bullshitter quotIt is impossible for someone to lie unless he thinks he knows the truth Producing bullshit requires no such conviction A person who lies is thereby responding to the truth and he is to that extent respectful of it When an honest man speaks he says only what he believes to be true and for the liar it is correspondingly indispensable that he considers his statements to be false For the bullshitter however all these bets are off he is neither on the side of the true nor on the side of the false His eye is not on the facts at all as the eyes ofthe honest man and of the liar are except insofar as they may be pertinent to his interest in getting away with what he says He does not care whether the things he says describe reality correctly He just picks them out or makes them up to suit his purposequot 11810 Philosophy Critical Thinking amp Logic Although pop culture is often derided for lowbrow humor there are some examples of critical thinking in many aspects of it South Park often depicts the boys addressing an important issue by thinking critically about it while the parents blindly follow popular opinion fads etc See quotThe Biggest Douche in The Universe Philosophy Critical Thinking amp Logic W K Clifford 184579 writes in his famous essay quotThe Ethics of Belief that quotEvery time we let ourselves believe for unworthy reasons we weaken our powers of selfcontrol of doubting ofjudicially and fairly weighting evidence He concluded that it is therefore quotalways wrong everywhere and for anyone to believe anything upon insufficient reason Philosophy Critical Thinking amp Logic Basic Distinction of Rational Inquiry Believing on the basis of rational grounds and evidence for belief reasoning and evidence vs believing on the basis of insufficient evidence Of central importance in philosophy is not simply holdingespousing a philosophical belief but supporting it with wellreasoned argumentation 11810 Philosophy Critical Thinking amp Logic Good Reasons to Think Critically Bad reasoning often has negative consequences Avoid being duped by propaganda indoctrination ideological thinking selfdeception etc Avoid biased and prejudiced thinking Develop independent creative critical reflective and analytical reasoning skills ie leadership skills Philosophy Critical Thinking amp Logic I Recall what Stephen Colbert calls quottruthinessquot Another key distinction in rational inquiry is the difference between what happens to be our personal attitudes towards or about a belief and thejustification or rationaland evidential grounds for the objective truth of that belief Our focus is on the latter Philosophy Critical Thinking amp Logic Everybody has philosophical beliefs and intuitions ie nonempirical beliefs and presuppositions about morality free will religion knowledge etc but we acquire many ofthese beliefs prior to having examined the relevant issues ourselves or before we are familiar with many key principles of logic or critical thinking So this raises the question Are your beliefs reasonable and wellfounded Philosophy Critical Thinking amp Logic The findings of empirical studies on how people think through controversial issues show that while human beings have a capacity for reasoning we are not by default all that good at it In fact we are prone to con rmation bias and motivated reasoning Unduly dismissive of evidence to the contrary of our preferred view confirmation bias Prone to inferred justification and error when reasoning about subjects in which we are emotionally invested Overestimate bias in other people when they espoused views different from our own and underestimate our own biases 11810 Philosophy Critical Thinking amp Logic Once in classlasked How we can tell whether or not e b39 Sed 39 A student quickly and con dently answered i know it s biased ifit is differentfrom biased reasoning or it it a recipe rcr confirmation bias Philosophy Critical Thinking amp Logic Because we form many of our beliefs before we have any rst hand knowledge of the principles of critical thinking and logical reasoning or even an examination 0 a 39 39 ormed ese ts Soan excellent pacities for critical thinking and logical analysis is by consi ering our 39 ophical beliefs But this also means we mus ewear 0 our own prejudic s biases etc and think critically to avoid confirmation bias motivated reasoning Philosophy Critical Thinking amp Logic I The OutsiderTest for Philosop l Beliefs Critically examining the arguments and evidence for and against a belief without presupposing the truth of your preferred view By doing so we can help compensate for conformation bias and avoid motivated reasoning Philosophy Critical Thinking amp Logic Identify some of your philosophical beliefs about morality knowledge religion science politics What are the reasonsthat you originally accepted these beliefs How confident are you on a scale of 1 to 10 that these are good reasons for the truth of that belief After we finish the section on informal fallacies examine your reasoningto determine whetheryour reasoning contains any such errors Arethe premises true 11810 Philosophy Critical Thinking amp Logic in logic an argument is a group of propositions at least one of which the premises is said to supportthe truth ofthe other the conclusion An argument has three main partse premise 5 Conclusion and an inference Classic Example of an Argument 1 All men are mortal lrremlsel 3 rherelore Socrates l5 7 lencluslpnl Philosophy Critical Thinking amp Logic Two Ways an Argument Can Fail 1 it it has at least one raise premise lunsouno uncogent or presupposition 2 it the premises even irtrue rail to logically imply thetruth orthe intended conclusion Le a fallacy Philosophy Critical Thinking amp Logic quotAn argument whose premises do not support its conclusion is one whose conclusion could befalse even if all its premiseswere true In cases orthis kind the reasoningis bad and the argument is said to be iallacious A tallacy is an error in reasoning As logicians use the word fallacy however it designates not any mistaken interence or raise belief but typical discourse andthat deuastatethe arguments in which they appear 39 type or argumentthat may seem to be correct but that r es n examination notto be so lCopi11575 Philosophy Critical Thinking amp Logic Watch quotthe Chewbacca is the Chewbacca defense a rationally 39 me claim that Chef wrote the song Explain your swer 11810 Philosophy Critical Thinking amp Logic Philosophy Critical Thinking amp Logic I quotThe Chewbacca Defense is an example ofa red herring fallacy In a red herring fallacy someone uses claims n argumen s that ave nothing to do with the issue at hand in orderto get someone raw a conclusion that they believeto be true Chewbacca lives is logically irrelevant to an a distraction from the question ofwhether Different Categories of Fallacies Fallacies of Relevance Appeal to emotion appeal to force ad hominem appeal to tradition genetic fallacy argument ad populism bandwagon Fallacies of Presumption False dichotomy circular reasoning straw man false cause suppressed evidence the record company stole Chefs song See quotTh FallaCIes of AmbigUIty e Chewbacca Defense A South Equivocation amphiboly composition division Park Logic Lesson Philosophy Critical Thinking amp Logic Philosophy Critical Thinking amp Logic Stephen Colbert s notion of truthiness is basically an Appeal to EmOtlon Pltyl39 appeal to emotion fallacy Chris I know that l have not had the best thlCh 0cm th the 35k attendance in class and have done horrible on O Presentmg 6 nce almost all of the assignments But if I get another rational argument is repiaced with the use of D then Will loose my scholarship and have to GXPFGSSiV language and move back home with my parents Surely you other dev39cescalcmated to do not want me to have to move back home it excite enthusiasm excitement anger pity etc would be humiliating for me and can see your to persuade the audience to way fit to give me a Cquot accept some conclusion 11810 Philosophy Critical Thinking amp Logic Philosophy Critical Thinking amp Logic The appeal to false or inappropriate authority fallacy occurs when the arguer appeals to parties with quotno legitimate claim to authority in the matter at hand See this clip of Steve Carell on The Daily Show for another example of exposing the appeal to emotion fallacy in advertising 39 Appeal to False Authority quotGeorge W Bush was a way better President than Reagan my Dad says so Philosophy Critical Thinking amp Logic Philosophy Critical Thinking amp Logic The appeal to consequences fallacy occurs 39 From The Daily Reveille letters to the editor when an arguer claim that a belief is falsetrue 113007 in WhiCh a StUdent Offers the because it has consequences they perceive to following reason against teaching Evolution be undesirabede5irabe quotThirdly I can think of nothing better than to o teach our children that they and their lives TherefOre X iS true grown up germs That39s what evolution teaches Why care about yourself or others if we are all just accidents of nature with no more value than that of a virus EX Belief in X leads to bad consequences Therefore X is false 11810 Philosophy Critical Thinking amp Logic The appeal to force fallacy occurs when a threat of harm is given as the reason for accepting or rejecting some conclusion recall the difference between prudential and evidential reasons Appealto Force quotIf you do not agree thatthe LSU Tigers are a great football team then I39ll kickyourass quotIf you do not give me an 39A39 in philosophythen I39ll tell the Dean that you sexually harassed me Philosophy Critical Thinking amp Logic The appeal to tradition argumentum ad antiquitatem fallacy occurs when an arguer appeals to the fact that some conclusion correlates with some long held belief tradition or custom This fallacy occurs when an arguer claims 39X must be righttrue because we ve always done it that way The fallacy relies on two questionable assumptions that 1 the original reasons given for X were correct and 2 pastjustifications are still relevant Philosophy Critical Thinking amp Logic Appeal to Tradition quotMarriage has always been defined as a union between one man and one women Thus marriage must continue to be defined as a union between one man and one women and we should not legally permit homosexuals to marry Appeal to the People The appeal to the people or bandwagon or appeal to the people fallacy argumentum ad populum occurs when a proposition is asserted to be true because many people believe it is true Just because a lot of people believe X is true does not in fact mean that it is true Likewise merely because only a few people believe something does not count against its truth The number of people that believe a proposition is true is irrelevant to whether or not it is in fact true 11810 Appeal to People Appeal to the People quotThe Inquisition must have been justified and beneficial ifwhole peoples invoked and defended it if men ofthe loftiest souls founded and created it severally and impartially and its very adversaries applied it on their own account pyre answering to pyre Ad Hominem Abusive The ad hominem or attack against the person abusive attack occurs when the quotthrust is directed not at a conclusion but at the person who asserts or defends itquot In other words this fallacy occurs when the person themselves is attacked rather than their argument or claims In this kind offallacy a person advances a claim then another arguer attacks their person in an effort to show that the original claim is false Ad Hominem Ad Hominem Abusive quotWe should reject Mr Smith39s arguments for raising taxes He s nothing but a tax and spend liberal quotWe should reject Bush39s foreign policy He39s just a right wing nut bag Ad Hominem Circumstantial In the circumstantial form of the ad hominem fallacy it is the irrelevance ofthe connection between the belief held and the circumstances of those ho ding it that gives rise to t e mistake The circumstances of one who makes or rejects some claim have no bearing on the truth of that claim In one of the varieties of this form it is argued fallaciously that consistency obliges an opponent to accept or reject some conclusion merely because oft at erson s employment or nationality or political affiliation or other circumstances Copi 11810 Ad Hominem Circumstantial Ad Hominem Circumstantial quotThe CEO of Chevrolet says in his commercial that Chevys are the best cars that money can buy Obviously that39s not really true and he39sjust sayingthat because if people believe it and buy Chevys then he39ll make a lot of money Ad Hominem Tu Quoque Tu Quoque fallacy is another version of an ad hominem fallacy It occurs when an arguer contends that some belief is false because it is inconsistent with some other claim held or action performed by that person Ad Hominem Tu Quoque Tu Quoque Fallacy Dad quotYou know son you should not experiment with drugs You might do some damage to your cognitive development Child quotBut Dad you said yourselfyou experimented with drugs in college So it s false that I should not try them Guilty by Association The guilty by association fallacy occurs when an arguer concludes that one person is guilty in virtue of some relationship irrelevant to the truth of the conclusion 1 Y is a X 2 Y is associated with Z 3 Thus Z is an X 11810 Guilty by Association Guilty by Association Fallacy quotHitler was a vegitarian Hitler was evil You39re a vegitarian Therefore you re evil Straw Man Fallacy The straw man fallacy occurs when an arguer presents a distorted or mischaracterized interpretation ofa rival position criticizes the mischaracterized version then claims to have defeated the position altogether For example if an arguer presents an oversimplified and mischaracterized interpretation oftheir opponents position shows how it39s selfdefeating then claims to have defeated all versions of that idea Straw Man Fallacy Straw Man Fallacy quotMr Goldberg has argued against prayer in public schools Obviously Mr Goldberg advocates atheism But atheism is what they have in Russia Atheism leads to the suppression of all religions and the replacement ofGod by an omnipotent state Is that what we want forthis country I hardly think so Clearly Mr Goldberg39s argument is nonsense I Appeal to Ignorance The appeal to ignorance fallacy occurs when quotit is argued that a proposition is true simply on the basis that it has not been proved false or that it is false because it has not been proved truequot Appeal to Ignorance quotNobody currently knows whether or not alien life exists So it s probably true that it does 11810 Appeal to Personal Incredulity The appeal to personal incredulitylack of imagination fallacy occurs when one arguer appeals to their personal disbelief as a basis for accepting or rejecting a conclusion Appeal to Personal Incredulity quotI just cannot imagine how life could have emerged naturally without some intelligent designer at work in the universe Therefore some intelligent designer must have created life Appeal to Negative Proof The appeal to negative proof is another version of an appeal to ignorance fallacy It occurs when one arguer asserts that a claim is true unless it is refuted or disproven 1 You cannot disprove X 2 Therefore X is true Appeal to Negative Proof Appeal to Negative Proof 1 If you cannot disprove the existence of chemtrails then it is true that the government is spraying chemicals in the atmosphere to control the weather N You cannot disprove the existence ofchemtrails EquotJ Therefore it is true that chemtrails exist and the government is spraying chemicals in the atmosphere to control the weather Genetic Fallacy The genetic fallacy occurs when an arguer appeals to the origins ofa belief or practice as a justification for accepting or rejecting it as true quotYou know who invented genetic engineering The Nazis that39s who Clearly then genetic engineering or eugenics is immoral and an evil authoritarian practice And it should be prohibited by law 11810 Hasty Generalization The hasty generalization fallacy occurs when we draw a general conclusion about an entire group based on an unrepresentative sample Le stereotyping Hasty Generalization quotI39ve met five New Yorkers and they were all rude Therefore it s probably true that all New Yorkers are rude False Cause The false cause fallacy occurs when an arguer contends that one event caused another event simply because the two events occurred in close temporal succession correlation is not causation False Cause quotMy mother was very sick So I offered a sacrifice to the gods in her name and then she got better Clearly the gods rewarded my sacrifice and made r well Weak Analogy I The weak analogy fallacy occurs in an argument by analogy In this type of inductive argument two events or p enomena are com ared with one another and because they share certain features it is argued that if one has Y That the other is probably Y too The fallacy occurs when there is a relevant dissimilarity etween the two things compared that is relevant to the truth ofthe conclusion Weak Analogy Water is a liquid Whenyou dip a lit match into water it goes out Gasoline is also a liquid 50 probably whenyou dip a lit match into gasoline it will probably go out tooquot quotl e Weak Analogy WeakAnal gVFallazyhlszolumntoraweakanalo ralla ould nddle arr a number or examplesthat would make sense m me and mners wna are saelallvmnselausapauunesmlexal lssuesraeln Amenea spaarmlnarmesanelmmlgrants pm lnstead lwllluse LSUtomballas an analogy ormodemr ayslavery Le ssay hypothetlzallyhattlzketsarebelngsoldtorSDeazhwe all knowthey re not pm slnze most otvou are nvpersensmve about rampall we Mll Lunhe athletl department a break The stadlum sea592ADD people Atleatlzket and amll stadlumthe protltls sazA000mr onegame rm doesnotlrlzlude eaneessmns lju parapnemalla andthe prlzesome people ne here are mughlleD players evemseasan Eaen player a repuwldedwlthultlonhouslng ooksamealplanand r lnrstate athleteswhlzh makes up more than half ll a m the teamzome ab uKSJDDDDayearperathlete Solnoneyeartheathlet department is elsnlng out about 1 000 00ln senalarsnlpswnlen lime revenuet om onegame on lzlatsalo e nottomentlonDrporatespons rs Aunrmngm usAT NCAA averagesbetterthanhaltabllllondollarsayearl r e TVrl nm l 5 basketballmumame aK evenu r m ed 104000000 We have a model for pavrng players la eallee pmtesslonal sportsquot CAAVresldentlelesBrandsald lt ssoeaw ramanwholsmaklngmllllonsotdollarsa yearodlsmlsstheworkethl otzolleglateathletes Thevuth lime penentag o protesslonal athletesthat o rolsvewlow lnsteadthe malonwotthese athletes btall 5 Mb mu sleavethetleldzoun9oolorvazkwlthaserlesnfpalntuland m em 0 ng mentalandphyslzalreuwewperlod Astaraslammnzemed r l lsmodemrdavslavew 11810 Complex Question The complex question fallacy occurs when a question is asked in such a way as to presuppose the truth ofsome conclusion already contained in the question itself quotThe question itself is likely to be rhetorical no answer being genuinely sought But putting the question seriously thereby introducing its presupposition surreptitiously often achieves the questioner s purpose faaciousyquot Complex Question Complex Question Chris quotHow long have you been cheating on your wife Complex Question The complex question fallacy occurs when a question is asked in such a way as to presuppose the truth of some conclusion already contained in the question itself quotThe question itself is likely to be rhetorical no answer being genuinely sought But putting the question seriously thereby introducing its presupposition surreptitiously often achieves the questioner s purpose faaciousyquot Slippery Slope The slippery slope fallacy occurs when an arguer claims that X will cause Y but there is insufficient evidence to suggest that X will in fact cause Y to occur as Suggested Slippery Slope quotImmediate steps should be taken to outlaw birth control immediately Continued access to birth control will surely lead to an increase in promiscuity which in turn will cause an increase in divorces The increase in divorces will ultimately erode the moral fabric of society and cause the collapse of society 11810 Philosophy amp Critical Thinking In this clip from The Daily Show Jon Stewart claims Bill Bennett is guilty of a slippery slope fallacy in regard to the debate over same sex marriage Is he correct Are there other arguments that can be given for the same position on same sex marriage False Dichotomy The false cause fallacy is committed when an arguer presents two alternatives as ifthey exhaust all the possible options when in fact that do not exhaust all available options When an argument ofthis form does not exhaust all the logical possibilities then it commits the fallacy of false dichotomy False Dichotomy False Dichotomy quotEither morality is based on religion or anything goes You reject religion Thus you must believe that anything goesquot quotYou either agree with the President s policies on terrorism or you support terrorism You disagree with the President s policies Thus you support terrorists Composition The fallacy of composition occurs when we move erroneously move from what is true of a part of the whole and assert that it is true of the whole Composition Fallacy quotDell Computers is a very successful company just got a job at Dell So I m going to be successful tooquot 15 11810 Division The fallacy of division occurs if an arguer engages in reasoning that erroneoust claims that what is true ofthe whole must be true of the parts as well Division quotYou should not give me a ticket Officer Policemen work forthe taxpayers I39m a taxpayer So you work for me and I do not think I deserve a ticket Circular Reasoning The begging the question or circular reasoning fallacy occurs when an arguer s premises presuppose the truth ofthe conclusion which they are attempting to establish Circular Reasoning Circular Reasoning quotThe Book of Mormon is true because it was written by Joseph Smith Joseph Smith wrote the truth because he was divinely inspired We know that Joseph Smith was divinely inspired because the Book of Mormon says he was and the Book of Mormon is true I Equivocation The fallacy of equivocation occurs when two or more meanings ofa term are confused or conflated in the course of an argument Equivocation quotA plane is a carpenter39s tool A Boeing 737 is a plane Thus a Boeing 737 is a carpenter s tool 11810 Amphibon An amphiboly fallacy occurs when the awkward or loose phrasing of a sentence lends itself to dubious or questionable interpretations Amphiboly quotCroesus went to the muse to ask advice about going to war and the muse responded quotIf Croesus went to war with Cyrus he would destroy a mighty kingdom Croesus interpreted this in his favor and so he went to war but he ended up destroying is own kingdom Two More Fallacies There are two other fallacies we should keep in mind the stacked or suppressed evidence fallacy and the special pleading fallacy SuppressedStacked Evidence The suppressedstacked evidence fallacy occurs when an arguer presents a onesided case for a conclusion that ignores or omits other relevant evidence counting against their intended conclusion thereby making the case for it appear stronger than it is in fact Spotting this fallacy often requires either already knowing a good deal about the subject ofthe argument or additional research Special PleadingDouble Standard The special pleadingdouble standard fallacy occurs when an arguer applies one set of standards to views that they do not accept for their own position without offering any reason for excluding their preferred View from the same standards For example an arguer demands a higher standard of evidence for positions they do not hold and a lower burden of proof for positions they favor Special PleadingDouble Standard Suppose someone argues that while in general it is a good idea to base your beliefs on good reasons and sufficient evidence but then claims in regard to some particular set of beliefs that they must be accepted without evidence or sufficient reason by everyone This would constitute without any good reason why we should adopt a different standard in this case an instance of special pleading Practice Exercises 1 I simply cannot imagine why anyone would doubt the existence of God Therefore it must be the case that there are no good arguments supporting atheism or agnosticism N quotThis country was founded on Christian beliefs Therefore our laws ought to promote Christian values and conduct Practice Exercises 3 quotIf you smoke marijuana then eventually you will try stronger and more dangerous drugs You39ll start experimenting with pills cocaine and eventually heroine So if you smoke that join you39re going to end up a heroine addictquot quotFeminists argue for equal opportunity and treatment in for women in society So feminists believe that the only measure of success is in the workplace Doing so is demeaning to stayathome moms These feminists are against mothers raising their children Clearly their arguments are completely ridiculous since there is obviously nothing demeaning about staying at home to raise a familyquot Jgt Critical Thinking amp Informal Fallacies Fallacy Identification Watch Otter s defense from Animal House What is Otter s argument Does his argument commit any informal fallacies Explain 11810 18 11810 Critical Thinking amp Informal Fallacies You can find an more extensive list of fallacies online hei Now that you re a little more familiar with some basic errors of reasoning reconsider the reasoning you gave forthe philosophical belief you identified earlier Did your reasoning commit any informal fallacies Did it contain any false premises Note you might have to learn more about the relevant topic and issues in orderto determine whether there s a false premise Basic Logic Arguments come in different types Deductive Argument modus ponens modus tollens etc Non Deductive Argument inductive generalization argument by analogy abductive reasoning How you evaluate an argument will depend upon what kind of argument it is Deductive Arguments Deductive Argument an argument in which the truth of the conclusion is said to follow necessarily follows from the truth of the premises Basic Logical Symbolization for Formal Logic p q r s are used as place holders for parts of propositions Upper case letters are used as symbols for actual propositions 3 Conditional statement V Disjunction N Negation Conclusion symbol 11810 Basic Forms of Deductive Argumentation Modus ponens Modus toens Disjunctive syllogism Big constructive dilemma Hypothetical Syllogism Modus Ponens Modus Ponens Argument p 7 1 If MLK was assassinated p then he is dead q 2 MLK was assassinated p 3 Therefore MLK is dead q This argument has the following form 1 p Dq 2 p 3 q Modus Ponens Modus ponens has two premises One is always as conditional statement or an quotif thenquot statement The first part of a conditional statement is the antecedent ex quotIf MLK is assassinated The second part ofthe conditional is consequent ex quot then MLK is deadquot H wzv 9quot Other Forms of Modus Ponens If you do not study then you will not pass the class Jenny did not study Therefore Jenny will not pass the class NP 3 Nel Np 39q 20 11810 Other Forms of Modus Ponens Modus Tollens 1 P Like Modus Ponens Modus Tollens has two 2 p D Nq premises one of which is a conditional the 3 q complex premise and another premise the simple premise that negates the consequent 4 Billy has his seatbelt on Of the conditional 5 If you wear a seatbelt then you will not get a p Dq ticket q now 6 Billwill not getaticket Nplnm P Modus Tollens Other Forms of Modus Tollens 1 lfGreat Britain won the Revolutionary War then 1 If you have no money then we can not get any the United State is still subject to British rule concert tickets 2 The US is not still subject to British rule 239 We got concert tickets 3 Thus Great Britain did not Win the Revolutionary 339 Thus you had money 439 p 3 q 4 Np D Nq 539 q 5 q notice that quotqquot here is the negation ofthe 639 consequent in the first premise 6 p 21 11810 Forms of Modus Tollens q NPDCI In this form the complex and simple premises are inverte 1 N E Disjunctive Syllogism Either George Washington was the first US president gAbraham Lincoln was the first US president Abraham Lincoln was not the first US president Thus George Washington was the first US president Disjunctive Syllogism In a disjunctive syllogism the one premise is an either or claim and the other premise negates one part ofthe either or claim The negation of either one of the disjunctives derives the other disjunct as the conclusion H Forms of Disjunctive Syllogisms PVq 22 11810 Disjunctive Syllogism 1q 2vaNq 3 39 Np Notice in these versions the disjunctive premise and the simple premise are inverted r4 4 PE WHP39P39 Big Constructive Dilemma Eithertubaccu advertising is curtailed 1P arteenage srnaking increases 1Q lftubaccu advertising is curtailed 1P tnen cigarette carnpanieswill lay off workers in lfteenage srnaking increases id lung cancerrates will raise ls Thus either cigarette manufacturers will lay off warkers in or lung cer rates will raise ls 1 2 3 4 Constructive Dilemma PvQ PDR QDS RvS The idea ofa constructive dilemma is that we begin with two alternatives either or then take each as an antecedent of a conditional if then and concludes that with the consequent of each conditional Other Forms of Constructive Dilemma PENN PENN pVNp pDr NpDr 23 11810 2 Equot EquotJ Pquot Hypothetical Syllogism lfinfanticide is immoral then lateterm abortions are immoral If late term abortions are immoral then early term abortions are immoral Thus ifinfanticide is immoral then early term ortions are immoral p D r r s 39 p D s Valid argument a deductive argumen Evaluating Deductive Arguments Recallthat an argument canrail in one or two ways 11 contain a raise claim lunsounduncogent or 12 the premises 7 even it true a can rail t imply thetruth ofthe conclusion lfallacious 39 39 39 39 l meir four or structure Deductive arguments have either a valid or invalid form tin which it is impossible rorrhe premises to be true and the conclusion to be false So it it is possiblerorthereto petrue premises and a raise the argument is in lid r conclusion Evaluating Deductive Arguments You can have a valid argument with any combination oftruefalse premises conclusion except in which the premises are all true and the conclusion is false then it is invalid So for example an argument can have all false premises and a false conclusion and still be valid 2 N EquotJ Evaluating Deductive Arguments then he is dead tr Jimmy Buffet has not be killed in a plane crash true Thus Jimmy Buffet is not dead true All the claims in this argument aretrue but the argument is invalid because it is possible to have an argument with the same form in which the premises are true and the conclusion is false IfJimmy Buffet has been killed in a plane crash ue 24 11810 Evaluating Deductive Arguments I The Jimmy Buffet argument has the followingform 1 qu 2 p 3 q I But it is possible to forthe premises to be true and the conclusion to be false with this argument form Recall the definition of validity is the impossibility oftrue premises and a false conclusion Evaluating Deductive Arguments Consider the following argument with the same form as the Jimmy Buffet argument 1 If George Washington was assassinated then he is dead true statement 2 George Washington was not assassinated true statement 3 Thus George Washington is not dead false statement Evaluating Deductive Arguments The Jimmy Buffet and the George Washington arguments have an invalid form because it is possible to develop an argument with the same form that has true premises and a false conclusion then the argument form is shown to be invalid Recall that validity is defined as the impossibility of having true premises and a false conclusion Evaluating Deductive Arguments In fact any argument in the form ofthe Jimmy Buffet and the George Washington arguments is invalid It has an invalid form called denying the antecedent This is a fallacious form of reasoning that appears similar to valid forms of argument but that violates the definition of validity 25 11810 Evaluating Deductive Arguments Denying the antecedent is a formal fallacy Any argument that has this form is invalid regardless of the content 1 P DO 2 NP 3 NQ Evaluating Deductive Arguments Affirming the consequent is another formal fallacy Any argument that has the following form is invalid regardless of content 1 P D Q 2 Q 3 P Evaluating Deductive Arguments To evaluate a deductive argument what is required is to see if it is possible to develop an argument with the same form as the argument present but in which there are true premises and a false conclusion This is called the quotcounterexamplequot method The content isn t important just the logical structure ofthe argument CounterExamples Whenever you are presented with a deductive argument if you can show that it is possible to develop an argument with the exact same form as the one given but in which it is possible to have true premises and a false conclusion then you39ve shown the original argument to be invalid thereby giving reason to reject it 26 11810 Argument by Analogy I An argument in which a conclusion about an object or event is allegedly established as probably true by noting similarities between it and another object ofevent Argument by Analogy quotJane and Nancy were both awarded National Merit Scholarships and both are math majors who love mathematics both also appreciate Professor Smith39s approach to teaching Jane did extremely well in Smith s calculus class and received an A Therefore Nancy will probably receive an A as wellquot p 22 7 Argument by Analogy quotHamlet and Macbeth are both plays written by William Shakespeare They are two plays written in Elizabethan English are about the same length Mary was able to read Hamlet in one evening Therefore it is likely that she will be able to read Macbeth in one evening as wellquot p22 8 Argument by Analogy I First the proposed similarity between A and B must be relevant to establishing the conclusion I Second A and B must not be dissimilar in any important way that would make the conclusion unlikely given the premises offered I Both 7 and 8 are strong arguments from analogy There39s no reason additional info to assume a dissimilarity 29 11810 Argument by Analogy quotWhen a lighted match is slowly dunked into water the flame is snuffed out But gasoline is a liquid just like water Therefore when a lighted match is slowly dunked into gasoline the flame will be snuffed outquot p 23 Arguments by Analogy quotMars is similar to the earth in that both are planets that orbit the sun Living things inhabit the Earth Therefore living things inhabit Marsquot p 23 l Equot 3 Argument by Analogy Human artifacts are complex orderly and purposeful which is explained by the fact that they were designed by intelligent beings Like human artifacts parts of nature are complex orderly and purposeful Therefore probably the complexity orderliness and purposefulness of parts of nature is explained by them beingthe products of intelligent design Induction vs Abduction Abduction and induction are both non deductive forms of argumentation Abductive Argument a nondeductive argument in which a theory allegedly is established as likely to be true because it provides the best explanation for some phenomenon also known as quotreasoning to the best explanationquot 30


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