Chapter 25: Quiz — Logic, Argumentation, and Fallacy Recognition

Instructions: Answer all questions. For multiple choice questions, select the best answer. For short-answer questions, write 1-3 sentences. Answers are hidden at the bottom of this file.

Part I: Multiple Choice (Questions 1–14)

Question 1. An argument is valid if and only if:

(A) All of its premises are true. (B) Its conclusion is true. (C) It is impossible for all premises to be true and the conclusion false simultaneously. (D) It is persuasive to most audiences.

Question 2. Which of the following is an example of modus tollens?

(A) If A then B; A; therefore B. (B) If A then B; B; therefore A. (C) If A then B; not-B; therefore not-A. (D) If A then B; if B then C; therefore if A then C.

Question 3. "You claim that our food additives are unsafe, but you eat fast food every day — so your opinion is worthless." This is an example of:

(A) Straw man (B) Tu quoque (C) Ad hominem abusive (D) False dichotomy

Question 4. The Gish Gallop exploits:

(A) The audience's inability to evaluate any individual claim (B) The asymmetry between producing claims and refuting them properly (C) The fact that most claims in debates are false (D) Emotional manipulation of moderators

Question 5. Which of the following is a FORMAL fallacy?

(A) Ad hominem (B) Slippery slope (C) Affirming the consequent (D) Appeal to nature

Question 6. An argument is sound when:

(A) It is valid and its conclusion is true. (B) It is persuasive and factually accurate. (C) It is valid and all its premises are true. (D) It contains no fallacies.

Question 7. "Either we ban all social media platforms or we accept that children will be damaged by them." This argument commits which fallacy?

(A) Slippery slope (B) False dichotomy (C) Begging the question (D) No true Scotsman

Question 8. The post hoc ergo propter hoc fallacy involves:

(A) Attacking the character of the person making an argument (B) Inferring causation from temporal sequence alone (C) Circular reasoning where the conclusion is used as a premise (D) Misrepresenting an opponent's position to attack it

Question 9. Which of the following best illustrates the "no true Scotsman" fallacy?

(A) "Scotland is the best country in the world — any Scotsman will tell you that." (B) "Real scientists don't believe in climate change." "But Dr. X is a scientist and accepts climate science." "Well, Dr. X isn't a real scientist then." (C) "Scotland has better weather than England." "That's simply not true." "Well, you've never been to Scotland." (D) "Some Scotsmen are great athletes, so all Scotsmen must be athletic."

Question 10. What distinguishes abductive reasoning from deductive reasoning?

(A) Abductive reasoning is always stronger than deductive reasoning. (B) Abductive reasoning identifies the most probable explanation rather than guaranteeing a conclusion. (C) Abductive reasoning cannot be used in science. (D) Abductive reasoning always uses syllogistic structure.

Question 11. "We cannot prove that 5G towers DO NOT cause cancer; therefore they might." This commits:

(A) False cause (B) Appeal to ignorance (C) Begging the question (D) Slippery slope

Question 12. Cherry picking evidence is most closely related to:

(A) The straw man fallacy, because it misrepresents the true picture (B) The suppressed evidence fallacy, because it presents an incomplete evidential record (C) The appeal to authority, because it relies on selected expert opinions (D) The red herring, because it distracts from the main issue

Question 13. Which argumentative structure is used in modus ponens?

(A) If P then Q; not-Q; therefore not-P (B) Either P or Q; not-P; therefore Q (C) If P then Q; P; therefore Q (D) If P then Q; if Q then R; therefore if P then R

Question 14. "That medical treatment has been used for thousands of years, so it must be effective." This commits:

(A) Appeal to tradition (B) Appeal to nature (C) Hasty generalization (D) Appeal to authority

Part II: True/False with Justification (Questions 15–20)

For each statement, write TRUE or FALSE, then write one sentence justifying your answer.

Question 15. A valid argument can have false premises and a false conclusion.

Question 16. Denying the antecedent is a formal fallacy.

Question 17. The burden of proof always lies with whoever holds the skeptical position.

Question 18. An inductive argument is cogent if and only if it is strong and has true premises.

Question 19. The Gish Gallop is only effective in live debates, not in written media.

Question 20. Moving the goalposts is a form of the appeal to ignorance fallacy.

Part III: Fallacy Identification (Questions 21–25)

Question 21. Identify the fallacy and explain it in 2-3 sentences.

"Scientists say we should reduce sugar consumption. But scientists also said margarine was healthy and it turned out to be full of trans fats. So we can't trust scientists about what we should eat."

Question 22. Identify all fallacies in the following passage.

"Homeopathy must work. After all, it's been used for over 200 years, and millions of people worldwide use it. Conventional medicine is only interested in selling drugs, so of course they dismiss it. Show me a homeopathic remedy that has hurt someone — you can't. And many celebrities and athletes swear by it. The real question is why are doctors so threatened by it?"

Question 23. Identify the fallacy:

"If we allow physician-assisted dying in terminal cases, within a generation doctors will be euthanizing patients without consent, the elderly will be pressured to end their lives to avoid being a burden, and life will lose its fundamental value in our culture."

Question 24. Is this a valid argument? Is it an example of a formal fallacy? Explain.

"If a news source consistently publishes false information, it should not be trusted. CNN has never published a false story. Therefore, CNN should be trusted."

Question 25. Identify the implicit premise(s) and any fallacies:

"I've been taking echinacea every winter for five years and haven't had a serious cold. That's five years of evidence — echinacea prevents colds."

Answer Key

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ANSWERS

Part I: Multiple Choice

Q1: (C) — Validity is defined purely by the impossibility of true premises and a false conclusion simultaneously. It says nothing about whether premises are actually true (that's soundness) or whether the argument is persuasive.

Q2: (C) — Modus tollens: If A then B; not-B; therefore not-A. Option A is modus ponens; option B is the fallacy of affirming the consequent; option D is hypothetical syllogism.

Q3: (B) — Tu quoque ("you too") is a variant of ad hominem that deflects criticism by pointing out the critic's own alleged hypocrisy. The claim "you eat fast food" doesn't address the validity of the argument about food additives.

Q4: (B) — The Gish Gallop's core mechanism is the asymmetry: producing a fallacious or weak claim takes seconds; properly refuting it requires time, expertise, and evidence. A presenter deploying 50 claims in 20 minutes cannot be adequately rebutted in the same timeframe.

Q5: (C) — Affirming the consequent is a formal fallacy because it is an error in logical form: If P then Q; Q; therefore P. Ad hominem, slippery slope, and appeal to nature are all informal fallacies arising from content and context rather than logical structure.

Q6: (C) — Soundness requires both validity (correct logical form) and truth of all premises. A true conclusion is not sufficient — the argument could have a coincidentally true conclusion without valid inference. Absence of fallacies is related but not definitionally sufficient.

Q7: (B) — False dichotomy (false dilemma). The statement presents only two extreme options (ban all social media vs. accept child damage) when many intermediate regulatory, educational, and technical options exist.

Q8: (B) — Post hoc ergo propter hoc ("after this, therefore because of this") is the fallacy of concluding causation from temporal sequence. A precedes B, therefore A caused B — which overlooks the vast number of other events that also preceded B.

Q9: (B) — The no true Scotsman fallacy involves protecting a universal claim from counterexamples by definitionally redefining the category to exclude the counterexample, rather than revising the claim. Option B illustrates this perfectly.

Q10: (B) — Abductive reasoning identifies the hypothesis that best explains available evidence; it yields probable rather than necessary conclusions. Deductive reasoning guarantees conclusions given true premises. Abduction is foundational to scientific hypothesis formation.

Q11: (B) — Appeal to ignorance (argumentum ad ignorantiam): arguing that because something cannot be disproved, it might be true (or is true). The inability to prove a universal negative does not validate a positive claim.

Q12: (B) — Cherry picking is most accurately described as the suppressed evidence fallacy: presenting a selective portion of the evidence that supports one's conclusion while omitting disconfirming evidence. While it can involve misrepresentation (like straw man), the defining feature is selective evidence presentation.

Q13: (C) — Modus ponens: If P then Q; P; therefore Q. Option A is modus tollens; option B is disjunctive syllogism; option D is hypothetical syllogism.

Q14: (A) — Appeal to tradition: arguing that something is correct or beneficial because it has been practiced for a long time. Longevity of practice does not establish efficacy — many harmful practices persisted for centuries.

Part II: True/False

Q15: TRUE — A valid argument guarantees that IF the premises are true, the conclusion must be true. But validity says nothing about whether premises actually are true. Example: "All cats are robots. My cat is a robot. Therefore, something in this argument is invalid." Wait — that's valid! Both premises are (stipulatively) false, and the conclusion follows necessarily.

Q16: TRUE — Denying the antecedent is a formal fallacy: If P then Q; not-P; therefore not-Q. This is invalid because Q might be true via other pathways besides P.

Q17: FALSE — The burden of proof lies with whoever makes a positive claim, not with the skeptic. Skeptics are not required to disprove every speculative claim; the burden is on those asserting that something is the case. (Context and prior plausibility matter, but the basic burden principle favors the null position.)

Q18: TRUE — Cogency is to inductive arguments what soundness is to deductive arguments. An inductive argument is cogent if and only if it is strong (premises support conclusion probabilistically) and all premises are true.

Q19: FALSE — The Gish Gallop is equally effective in written media, YouTube videos, blog posts, and social media threads. A written article making 40 claims in rapid succession creates the same asymmetry: readers encounter a cascade of assertions, and addressing each thoroughly would require a much longer rebuttal that fewer people will read.

Q20: FALSE — Moving the goalposts is a distinct fallacy involving arbitrary escalation of evidential standards to prevent a conclusion from being established. Appeal to ignorance argues from inability to disprove. Though related (both can protect beliefs from evidence), they are structurally different tactics.

Part III: Short Answer

Q21: This commits hasty generalization (also related to the genetic fallacy and inductive weakness). The argument uses two specific instances where scientific consensus was revised (margarine and trans fats) to conclude that scientific guidance on diet generally cannot be trusted. This ignores the vast number of cases where scientific nutritional guidance has been accurate, misunderstands how science self-corrects, and conflates the fallibility of past claims with the untrustworthiness of all current ones.

Q22: The passage contains multiple fallacies: - Appeal to tradition: "used for over 200 years" - Bandwagon/appeal to popularity: "millions of people worldwide use it" - Ad hominem / circumstantial ad hominem: "Conventional medicine only interested in selling drugs" (attacking motivations rather than evidence) - Appeal to ignorance: "Show me a homeopathic remedy that has hurt someone — you can't" (inability to prove harm does not establish safety; also, homeopathic remedies have caused harm through delayed treatment) - Appeal to authority (celebrity): "many celebrities and athletes swear by it" (celebrities lack medical expertise) - Loaded question / ad hominem: "why are doctors so threatened by it?" (assumes threat rather than legitimate scientific skepticism)

Q23: This is the slippery slope fallacy. The argument moves from a specific limited policy (physician-assisted dying in terminal cases) to a chain of increasingly extreme consequences (non-consensual euthanasia, systemic elder pressure, cultural devaluation of life) without providing evidence that each causal link is likely or inevitable. The inference requires independent justification of each step in the chain.

Q24: The argument form is: If P then Q; not-P; therefore Q. Wait — let's re-examine. The premises are: (1) If consistent false information → don't trust; (2) CNN has never published a false story; (3) Therefore, CNN should be trusted. This commits denying the antecedent only if we treat premise 1 as "If not consistently false, then trust" — but actually, the argument's validity depends on reading the conditional in a way that licenses the inference. More importantly, premise 2 is demonstrably false (all major news organizations have published errors). The argument is both formally suspect (the conditional doesn't support the positive conclusion directly) and unsound because premise 2 is false. It is not a clean example of a named formal fallacy, but it demonstrates how false premises produce unsound arguments even if the logical structure might be reconstructed.

Q25: Implicit premise: "Five consecutive winters without a serious cold is sufficient evidence to establish that echinacea prevents colds." This premise is false: (a) the sample size is one person; (b) there is no control condition — the person might not have gotten serious colds in those winters anyway; (c) the claim ignores regression to the mean, seasonal variation, other health practices, and definition of "serious cold." The argument commits anecdotal evidence and hasty generalization from a single non-controlled personal experience to a causal conclusion. Proper evidence would require a randomized controlled trial comparing echinacea users to matched non-users across multiple people and seasons.