University of Ottawa Faculty of Law (Civil Law Section) From the SelectedWorks of Hon. Gerald Lebovits July, 2016 Say It Ain’t So: Leading Logical Fallacies in Legal Argument – Part 1 Gerald Lebovits Available at: https://works.bepress.com/gerald_lebovits/297/ JULY/AUGUST 2016 VOL. 88 | NO. 6 JournalNEW YORK STATE BAR ASSOCIATION Highlights from Today’s Game: Also in this Issue Exclusive Use and Domestic Trademark Coverage on the Offensive Violence Health Care Proxies By Christopher Psihoules and Jennette Wiser Litigation Strategy and Dispute Resolution What’s in a Name? That Which We Call Surrogate’s Court UBE-Shopping and Portability THE LEGAL WRITER BY GERALD LEBOVITS Say It Ain’t So: Leading Logical Fallacies in Legal Argument – Part 1 o argue effectively, whether oral- fact.3 Then a final conclusion is drawn able doubt. The jury has reasonable ly or in writing, lawyers must applying the asserted fact to the gen- doubt. Therefore, the jury hesitated.”8 Tunderstand logic and how logic eral rule.4 For the syllogism to be valid, The fallacy: Just because the jury had can be manipulated through fallacious the premises must be true, and the a reasonable doubt, the jury must’ve reasoning. A logical fallacy is an inval- conclusion must follow logically. For hesitated. The jury could’ve been id way to reason. Understanding falla- example: “All men are mortal. Bob is a entirely convinced and reached a con- cies will “furnish us with a means by man. Therefore, Bob is mortal.” clusion without hesitation. which the logic of practical argumen- Arguments might not be valid, tation can be tested.”1 Testing your though, even if their premises and con- argument against the general types of clusions are true. For example: “All Great lawyers use fallacies exposes whether your logic is cats are mammals. Some mammals are sound logic to trump sound or unsound. Even more impor- excellent swimmers. Therefore, some tant, being aware of fallacies will tell cats are excellent swimmers.”5 It’s true the average argument. you when others are using fallacious that all cats are mammals. It’s also true arguments against you — and how that some mammals are excellent swim- 2. Denying the Antecedent you can best respond. This article will mers. But “the fact that cats are mam- This fallacy exists in if/then statements help lawyers identify potential falla- mals and that some mammals are excel- when a writer who denies an anteced- cies in arguments. lent swimmers doesn’t prove anything ent suggests that the reader should Good lawyers must craft persua- about the swimming ability of cats.”6 also reject the consequent. sive arguments that make sense. Great Two general groups of fallacies Example: If the subject of a contract lawyers use sound logic to trump exist: Formal fallacies, which are falla- is the transfer of an interest in land, the average argument. Great law- cious because they’re based on formal then the contract should be in writ- yers are well-versed in formal logic logic, and informal fallacies, which are ing. The subject of this contract is and the different ways of reasoning. fallacious because of their content. In not a transfer of an interest in land. That’s why great lawyers use induc- this two-part column, the Legal Writer Therefore, the contract shouldn’t be in tive and deductive reasoning in their begins with formal fallacies. In the next writing.9 arguments. Deductive reasoning is a issue of the Journal, we continue with The fallacy: A contract that doesn’t form of argumentation that presumes informal fallacies. transfer an interest in land doesn’t that if the premises of the argument need to be in writing. But other kinds are true, the conclusion must also be Formal Fallacies of contracts should also be in writ- true. Inductive reasoning is a form of In written or oral argument, “formal ing. Simply denying the antecedent is argumentation in which the premises fallacies are arguments that are defec- insufficient to deny the consequent. strongly support the conclusion. tive because of their form, without A syllogism is a common form of regard to content.”7 The following is a 3. Affirming a Disjunct argumentation that applies deductive list of formal fallacies and what makes This fallacy occurs when one premise reasoning. Familiarity with the form them fallacious. is true, but the writer suggests that the of syllogisms leads to strong argu- other must be false: A or B. A is true. ments. A legal syllogism should have 1. Affirming the Consequent Therefore, B is false. three clauses. Syllogisms start with This logical fallacy occurs when the Example: Morgan is a judge or an a single general premise, called the consequent is said to be true and thus attorney. Morgan is a judge. Therefore, major premise, stating the rule being that the antecedent must also be true. Morgan isn’t an attorney. applied.2 Then a second premise, Example: “If the evidence makes the called the minor premise, asserts a jury hesitate, then the jury has reason- Continued on Page 58 64 | July/August 2016 | NYSBA Journal The Legal Writer 7. The Base Rate 10. The “Hot Hand” Fallacy Continued from Page 64 The base-rate fallacy occurs when a This fallacy assumes that past suc- The fallacy: Morgan is a judge so writer “ignor[es] statistical informa- cesses or failures will dictate the same she can’t be an attorney. It’s possible tion” in making an argument. Instead outcome for future events. that Morgan is a part-time judge and a of relying on statistics, the writer uses Example: Ms. Thompson has won practicing attorney. A false assumption irrelevant information to suggest a his past five cases. Therefore, she has is drawn that if one clause is true, the conclusion.11 a “hot hand” and will inevitably win other must be false. Example: Judge Smith grants five the next case. percent of the motions before him. The fallacy: Because Thompson has 4. Denying a Conjunct Mr. Jones is our firm’s top attorney. been successful in her past five cases, A writer denies the conjunct when Therefore, Judge Smith will grant she’ll win her next case. This fallacy either the antecedent or the consequent Jones’s motion. is subtly different from the gambler’s is false but contends that the other The fallacy: Based on the statistics, fallacy. The past success or failure will must be true.10 Judge Smith grants only five percent of continue in the “hot hand” fallacy. In Example: The defendant is not both his motions. That Jones is a top attor- the gambler’s fallacy, you predict that guilty and innocent. The defendant is ney doesn’t ensure that Jones’s motion your luck will be different on the next not guilty. Therefore, the defendant is will be granted. outcome. innocent. Familiarity with the form of syllogisms leads to strong arguments. The fallacy: It’s logically wrong to 8. The Conjunctive Fallacy 11. Multiple Comparisons assume that because the defendant The conjunctive fallacy “indicates that This fallacy arises when statistical evi- is not guilty, the defendant must be the conjunction of two events is more dence is presented to support your innocent. The defendant might be likely than one event.”12 argument. Statistical evidence “cannot innocent, but the truth of both prem- Example: Ms. Anderson is a brilliant guarantee . the truth . [I]t can only ises doesn’t imply the defendant is law student who’s ranked number one provide that the answer is within a cer- innocent. Defendants found not guilty at her law school. Ms. Anderson will tain margin of error.”15 The more com- aren’t necessarily innocent. be likely both a law professor and an parisons one draws between condi- attorney when she graduates. tions, “the more likely it is that an erro- 5. Commutation of Conditionals The fallacy: Because Ms. Anderson is neous result will occur by chance.”16 A commutation of conditions switches an excellent law student, it’s likely she’ll Example: One hundred studies com- the antecedent and the consequent. be both a professor and an attorney. pared the crime rate between males Example: If the judge isn’t in the court- Concluding that Ms. Anderson will be and females. Eighty showed no signifi- room, then there’s no trial. Therefore, both a law professor and an attorney cant difference. Ten showed that males if there’s no trial, the judge isn’t in the is unwarranted from the premise that are twice as likely to commit crimes courtroom. she’s a brilliant law student. than females. Ten showed that males The fallacy: The judge is in the court- are half as likely to commit crimes than room only if there’s a trial. It’s pos- 9. The Gambler’s Fallacy females. Thus, males are more likely to sible that the judge is in the courtroom The gambler’s fallacy makes the commit crimes than females. when no trial is taking place. unwarranted assumption that “the The fallacy: The result that says odds for an event with a fixed prob- males are half as likely to commit 6. Improper Transposition ability increase or decrease depending crimes is ignored. From the 100 cited Improper transposition negates both on recent occurrences.”13 The gam- studies, one can’t conclude that males the antecedent and the consequent: bler’s fallacy specifically “deals with are more likely to commit crimes than If A, then B. Therefore, if not-A, then individuals’ predictions concerning a females. not-B. single event.”14 Example: If there’s an arsonist, Example: Mr.