PHIL-P100 Argumentation (Ch. 2-3) Notes
PHIL-P100 Argumentation (Ch. 2-3) Notes Philosophy P100
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This 5 page Class Notes was uploaded by Kathryn Brinser on Sunday February 14, 2016. The Class Notes belongs to Philosophy P100 at Indiana University taught by Pieter Hasper in Fall 2016. Since its upload, it has received 9 views. For similar materials see Introduction to Philosophy in Liberal Arts at Indiana University.
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Date Created: 02/14/16
P100 Chapters 2 and 3 Notes- Deductive, Inductive, and Abductive Arguments 1-14-16 Argument- several definitions o Heated discussion, verbal fight, sometimes mutual contradiction o Connected series of statements to establish a definite proposition Premises- series of true or false statements/assumptions meant to imply a conclusion Conclusion- something being argued for Analyzing an Argument o Identify overall conclusion C o Look for reasons given (premises); 2 possibilities Each separately is already enough for C- simple (one premise) or multiple (several) argumentation Some/all of premises together are enough for C- combined argumentation o Ask yourself: Why is this person saying this? What reasons are given? o Different from agreeing or not with what person says/whether it is true o Ex. Argument within argument Exam-like question: Identify the conclusion and the premises. For every sub-argument, determine whether it is deductive or inductive, and if inductive, what kind. o Ex. It’s a good thing that I left school, because I would have learned nothing from the teachers there: they were often badly prepared, because they spent all their time on their research, and they were rarely available for out-of-class conversation; moreover, they were just strange! Conclusion: It’s a good thing that I left school Premise: I would have learned nothing from the teachers there They were often badly prepared o They spend all their time on research They were rarely available for out-of-class conversation They were just strange! Evaluating an Argument o Good argument- rationally persuasive; gives substantial reason to think conclusion is true Don’t always provide good reasons Should have true premises AND good reason to believe conclusion (premises are relevant) 3 types of good arguments (treated as mutually exclusive): o Do the reasons given establish the conclusion? If not, can gap be easily filled? If yes, argument is correct/valid/cogent; are the conclusion(s)/premises acceptable? If yes, then argument is also sound (any type can be sound) o Sometimes more important to be correct than sound- why? Functions of Arguments o Discussion in order to convince/persuade/justify (You should believe X because Y and Z are so) Several parties do not have to have contrary positions Only work if argument is sound Failure of justification- possible doubt about conclusion not taken away; not justification for opposite view Common mistake- assuming if an argument fails, contrary view is better Proponent- wants to establish something (argues) Opponent- is skeptical; need not have own view One-Sided vs. Two-Sided Discussions One-sided- opponent does not have own view; waits to be convinced, wants to hear good reasons Two-sided- opponent also has view, is also proponent; two discussions o Proponent wants to convince opponent, but if he fails, that does not mean opponent/contrary view is right o Opponent also has to argue for their view o Possible for neither side to have good reasons o Explaining a view with premises (X is the case, because of Y and Z; Y and Z explain X) If explanation fails, there is by itself no reason to doubt/reject X; there might still be convincing reasons for believing X Common mistake- if explanation not good, the fact is not there o Establish connection between premises and conclusion If argument is correct, then it is true that if premises are the case, conclusion is the case If argument “P1, 2 …, therefore C” is correct, then statement “I1 P2, P …, then C” is true Truth/acceptability of premises irrelevant- hypothetical argument Deductive Arguments o Deductive argument- meant to establish conclusion so if premises are the case, conclusion must be the case; if so, argument is valid (deductively correct) o Validity Valid argument need not have actually true premises; can have false premises and conclusion Concerns relationship between premises and conclusions Differs from everyday meaning of “valid” (plausible or true); validity is property of arguments ONLY Ex. P: All fish swim → P: All sharks are fish → C: All sharks swim (valid, true) Ex. P: All particles have mass → P: All electrons are particles → C: All electrons have mass (valid, true) Ex. P: All plants have minds → P: All ladders are plants → C: All ladders have minds (valid, false) o Logical Form Argument is valid or not because of logical form it has; subject matter irrelevant Examples above all have same logical form, so all valid or all invalid (valid) P: All B’s are C’s → P: All A’s are B’s → C: All A’s are C’s o Invalidity Deductively invalid- occurs if any possibility conclusion could be false when premises true Can have invalid argument when all statements are true, just like valid argument with all false statements Ex. P: Emeralds are green → C: Lemons are yellow (invalid, true) Premise doesn’t absolutely guarantee conclusion is true; not related Ex. P: If Jones stands in heavy rain without an umbrella, then Jones will get wet → P: Jones is wet → C: Jones was standing in the heavy rain without an umbrella Imagining all statements true, still invalid; premises don’t guarantee conclusion must be true Every argument of logical form P: If A, then B → P: B → C: Ais invalid Ex. P: If Sam lives in Wisconsin, then Same lives in the United States → P: Sam lives in the United States → C: Sam lives in Wisconsin Same logical form, makes more clear why form invalid o Testing for Invalidity Ignore subject matter, isolate skeleton of argument See if you can invent argument with that logical form in which premises true/conclusion false If you can, every argument with this form invalid Invalid can often be made valid by adding premise(s) Ex. P: Smith lives in the United States → C: Smith lives in Wisconsin (invalid) o P: Smith lives in the United States → P: Everyone who lives in the United States lives in Wisconsin → C: Smith lives in Wisconsin (valid, second premise false, conclusion false) o In this case, invalidity fixed, but gets replaced with problem that premise is false Ex. P: Smith lives in Wisconsin → C: Smith lives in the United States (invalid- does not guarantee conclusion) o P: Smith lives in Wisconsin → P: Everyone who lives in Wisconsin lives in the United States → C: Smith lives in the United States o Making invalid to valid AND paying attention to truth of premises If you cannot make an argument valid without having false premises, question whether argument is fundamentally flawed o Form of Hypothetical Arguments Suppose premises P, Q, R “Inner argument”: if P and Q and R, then S Arrive at “inner” conclusion S Inner argument is hypothetical; part of larger argument for final conclusion Ex. Making decisions (1) Suppose determinism is true (everything is caused and made necessary by preceding events) (2) Therefore (1), our decision is caused and made necessary by preceding events (3) What is made necessary could not have been made otherwise (4) Therefore (2-3), our decision could not have been made otherwise (5) Our decision is free only if it could have been otherwise (6) Therefore (4-5), our decision is not free (7) Therefore (1-6), if determinism is true, our decision is not free o Reductio ad Absurdum argument- hypothetical deductive arguments used in these Ex. “There must be void; for if there were no void, there could not be motion, for lack of room to move to.” (1) Suppose there is no void (2) If there is no void, there is no room to move to (3) Therefore (1-2), there would not be motion (4) (3) is absurd- there is motion (5) Therefore (1-4), (1) is false; there is void Here, (1-3) is hypothetical “inner” argument Form of Reductio Arguments Suppose P; get inner argument Derive conclusion Q, which is absurd Therefore, P is false Only works if hypothetical inner argument from P to Q is correct Inductive Arguments o Inductive argument- meant to establish conclusion so if premises are the case, conclusion probably the case; if so, argument is cogent/strong (inductively correct) o Types of Inductive Arguments Classical induction- among sample of F things, x% of the F things are G; therefore among all F things, x% of F things are G Sample on which generalization made should be representative and randomly taken Ex. Argument: 75% of swans are white; take a sample of swans and see how many are white and how many are black; therefore, can draw conclusion for all swans based on statistics of sample Ex. BAD: All the swans I’ve seen in my life are white; therefore all swans are white. o Explanation: perhaps sample on which premise is based is not good/representative sample Inverse induction- among all F things, x% of the F things are G; therefore this F thing is, with x% chance, G More than just probable connection in premise OR probability mentioned in conclusion OR case is randomly chosen Ex. Suppose you know 75% of all swans are white; can infer from that supposed truth that if you encounter a swan, there is a 75% chance it will be white Ex. BAD: People stink around here; therefore, this person stinks too o Explanation: “here” is vague, do not know if person is from there; not necessarily true for every person anyways Analogical induction- X is like Y in being F, G, and H (have properties in common); Y is P; therefore (probably), X is P too Features F, G, and H should lead to/explain feature P Respects in which X and Y are similar relates to concern of argument Ex. Rulers are like scientists; they should do a good job and always acknowledge facts; if something holds for scientists, may assume it holds for rulers (ie. Scientists should always be honest, assume that rulers should be honest as well) o Not successful argument, but has correct form Ex. BAD: Trees are like people: they live, eat, breathe, multiply o People feel pain; therefore trees feel pain too o Explanation: feeling pain requires more than living, eating, breathing, multiplying Abductive induction or abductive argument- X is the best explanation for Y that is available; Y is the case; therefore, X is probably the case Explanation should take full account of all circumstances/facts Structure: there is a fact P; explanation Q would explain P; therefore Q is true Deductively invalid- follows affirming the consequent (P; if Q, then P; therefore Q) (below); truth of explanations can never be deduced Refutations of explanations can be deduced: If Q, then P; not P; therefore not Q If a consequence of explanation does not hold, explanation is false Ex. The sky is blue; the best explanation we know is that the light is dispersed in such a way that only blue light hits our eyes, not other colors; cannot think of a better one, so this is probably true Ex. BAD: simplest explanation for him not handing in paper is laziness; therefore he is lazy o Explanation: there can be a more complex explanation Relation Between Type and Function o Justifying arguments can be both inductive and deductive Deductive- person must accept conclusion if they accept premises; logical Inductive- person might not have to accept conclusion if they accept premises o Explanatory must be deductive OR be capable of being made deductive by supplying premises If something explains something else, it must cause it Explanation holds logically o Hypothetical arguments meant to be deductive Hypothetical establishes tight connection between premises and conclusion; deductive regards relationship between them Representing Arguments with Trees o Identify conclusion and immediate premises o Indicate whether premises can do the job by themselves (simple or multiple argument) or whether they cooperate (combined argument) o Allow for premises for premises (as sub-conclusion) Common Mistakes o Circular argument- presupposes somewhere the truth of the conclusion or has it as a premise Can be hidden somewhere or worded differently Conclusion becomes necessary to argue for conclusion Ex. R2 identical to conclusion, used as premise Q sub-conclusion based on presupposition of R2 = C as true, so Q becomes essential to arguing for C, but C is used in concluding Q first o Necessary and sufficient conditions Ex. “If it’s raining, the streets are wet.” It raining is sufficient condition for streets being wet Does not rule out other reasons Equivalent to “Only if the streets are wet is it raining” P being sufficient for Q = Q being necessary for P Mistake: denying antecedent P (If P, then Q; not P; therefore not Q) o “If it’s raining, the streets are wet. It’s not raining, therefore, the streets are not wet.” o Streets can be wet from other things Mistake: confirming consequent Q (If P, then Q; Q; therefore P) o “If it’s raining, the streets are wet; the streets are wet; therefore it is raining.” o Streets can have melting ice or previous rain on them without present rain Ex. “Only if it’s raining are the streets wet.” It raining is necessary condition for streets being wet Rules out other simultaneous causes, but it does have to be raining Ex. “If and only if it’s raining, the streets are wet.” It raining is sufficient and necessary condition for streets being wet Strongest of these; must be raining and only raining o Ambiguity Same words/sentences used in several premises or conclusion, but have slightly different meanings Ex. P: Sirius is a bright star. P: Stars should be treated with respect. C: Therefore Sirius should be treated with respect. “Stars” has multiple definitions Ex. P: Suppose something divisible is divisible everywhere P: Suppose it were then to be divided everywhere P: Then it would consist of points—which is absurd P: Therefore it cannot be divisible everywhere C: Therefore it must consist of divisible atoms Numbers can be divisible as well as matter “Divisible everywhere” can mean at same time (into points) or not (one part divided, then goes back together, can be divided somewhere else, then back together, etc.)