JD Juris Doctor: Logical Reasoning 2 — Questions and Answers
Question 1: A statute reads: 'No vehicle shall enter the park.' A court must decide whether a bicycle counts as a 'vehicle.' Which interpretive approach asks what the legislature intended by 'vehicle' at the time of enactment?
- Purposivist interpretation
- Originalist/intentionalist interpretation (Correct answer)
- Textualist interpretation
- Living constitutionalism
Correct answer: Originalist/intentionalist interpretation
Intentionalist (or original intent) interpretation focuses on the drafters' subjective intent at the time of enactment.
Question 2: Argument: 'If the defendant lied about his alibi, he is probably guilty. He lied about his alibi. Therefore, he is probably guilty.' What type of argument structure is this?
- Modus tollens
- Modus ponens (Correct answer)
- Affirming the consequent
- Denying the antecedent
Correct answer: Modus ponens
Modus ponens has the form 'If P then Q; P; therefore Q,' which matches this argument exactly.
Question 3: A legal brief argues: 'The majority of courts that have considered this issue ruled for plaintiffs; therefore, this court should too.' What logical weakness does this argument have?
- It commits the fallacy of equivocation
- It is an appeal to majority rather than to legal reasoning or binding precedent (Correct answer)
- It misapplies the rule of lenity
- It ignores the plain meaning canon
Correct answer: It is an appeal to majority rather than to legal reasoning or binding precedent
Appealing to majority opinion (ad populum) is not a substitute for legal authority or sound reasoning unless those decisions are binding.
Question 4: Under the LSAT-style logical reasoning framework, a 'necessary assumption' differs from a 'sufficient assumption' in that a necessary assumption:
- Alone guarantees the conclusion
- Must be true for the argument to work but does not alone guarantee the conclusion (Correct answer)
- Provides additional supporting evidence for a premise
- Is identical to the conclusion restated differently
Correct answer: Must be true for the argument to work but does not alone guarantee the conclusion
A necessary assumption is one the argument requires (cannot be false), but it doesn't single-handedly prove the conclusion.
Question 5: Courts use the canon 'expressio unius est exclusio alterius.' Applied to a statute listing dogs, cats, and birds as 'covered pets,' which animal would this canon suggest is NOT covered?
- A domestic rabbit (Correct answer)
- A stray dog
- A purebred Persian cat
- A parrot
Correct answer: A domestic rabbit
Expressio unius holds that the express listing of some items implies the exclusion of others not listed, so a rabbit—not enumerated—would likely be excluded.
Question 6: An argument is said to be 'valid' in formal logic. Which of the following best describes a valid argument?
- All premises and the conclusion are true
- If the premises are true, the conclusion must be true (Correct answer)
- The conclusion is highly probable given the premises
- The argument has been accepted by a court of law
Correct answer: If the premises are true, the conclusion must be true
Validity is a structural property: in a valid argument the truth of the premises guarantees the truth of the conclusion, regardless of whether the premises are actually true.
Question 7: A prosecutor argues: 'The eyewitness identified the defendant; DNA evidence is consistent with defendant's presence; therefore, defendant is guilty beyond a reasonable doubt.' A defense attorney best challenges this by showing:
- The argument uses deductive reasoning
- The evidence is consistent with alternative explanations that create reasonable doubt (Correct answer)
- The prosecutor relied on inductive rather than deductive logic
- The statute of limitations has run
Correct answer: The evidence is consistent with alternative explanations that create reasonable doubt
In an inductive argument like this one, even if premises are true, other possibilities remain—and the defense must show those alternatives raise reasonable doubt.
JD Juris Doctor: Logical Reasoning 2
A statute reads: 'No vehicle shall enter the park.' A court must decide whether a bicycle counts as a 'vehicle.' Which interpretive approach asks what the legislature intended by 'vehicle' at the time of enactment?