威威老師的閱讀教室：GRE邏輯推理 (GRE Logical Reasoning)
導航
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Section 1：Question Types
GRE 邏輯推理題 (Logical Reasoning) 共有五大題型，每種考查不同的推理能力。
1.1 Strengthen（加強題）
任務： 找到一個能支持或加強論證的選項。
常見問法：
- Which of the following, if true, most strengthens the argument?
- Which of the following provides the strongest support for the claim?
解題策略：
- 找出論證的前提 (premise) 和結論 (conclusion)
- 找出前提和結論之間的 gap（邏輯跳躍）
- 找到一個能 彌合 這個 gap 的選項
常見正確答案類型：
- 提供額外證據支持前提
- 排除其他可能的解釋（排除 他擇）
- 建立前提和結論之間的因果連結
1.2 Weaken（削弱題）
任務： 找到一個能削弱或反駁論證的選項。
常見問法：
- Which of the following, if true, most seriously weakens the argument?
- Which of the following casts the most doubt on the conclusion?
解題策略：
- 找出論證的 前提 和 結論
- 找到前提和結論之間的假設 (assumption)
- 找到一個能動搖這個假設的選項
常見正確答案類型：
- 提出替代解釋（他擇原因）
- 顯示因果關係可能相反
- 證明前提和結論的關聯不成立
- 指出樣本偏差或數據問題
1.3 Assumption（假設題）
任務： 找出論證所依賴的未說明前提。
常見問法：
- The argument depends on which of the following assumptions?
- Which of the following is an assumption required by the argument?
解題策略：
- 找出前提和結論
- 問自己：「要讓結論成立，必須假設什麼？」
- 使用否定測試法 (Negation Test)：如果否定某個選項後論證崩潰，那它就是必要假設
否定測試法範例：
- 原論證：「這個城市有更多警察，所以犯罪率下降。」
- 假設：警察的存在確實能減少犯罪
- 否定假設：警察的存在不能減少犯罪 → 論證崩潰 → 確認這是必要假設
1.4 Paradox / Resolve（矛盾解釋題）
任務： 解釋一個看似矛盾的現象。
常見問法：
- Which of the following, if true, most helps to resolve the apparent paradox?
- Which of the following best explains the discrepancy?
解題策略：
- 清楚識別矛盾是什麼（事實 A vs. 事實 B）
- 找到一個選項能同時與兩個事實相容
- 正確答案通常引入一個新的因素來解釋矛盾
1.5 Inference（推論題）
任務： 找出能從題幹中合理推出的結論。
常見問法：
- Which of the following can be properly inferred from the information above?
- If the statements above are true, which of the following must also be true?
解題策略：
- 正確答案 必須 為真，不能只是「可能」為真
- 避免過度推論
- 注意量化詞（all, some, most, none）
Section 2：Logical Reasoning Strategies by Type
2.1 Strengthen 策略
核心公式：
Premise → [ASSUMPTION] → Conclusion
↑
Strengthen here
步驟：
- 識別 Conclusion（通常在最後一句）
- 識別 Premise（支持結論的證據）
- 找到 Gap（前提未完全證明結論的地方）
- 選擇能 彌合 這個 缺口 的選項
2.2 Weaken 策略
核心公式：
Premise → [ASSUMPTION] → Conclusion
↑
Attack here (否定假設)
最有效的削弱方式：
- 他擇原因 (Alternative Cause)： 提出另一個可能導致結果的原因
- 因果倒置 (Reverse Causality)： 可能是結果導致原因，而非原因導致結果
- 第三因素 (Third Variable)： 另一個因素同時導致了「原因」和「結果」
2.3 Assumption 策略
兩種假設：
- 必要假設 (Necessary Assumption)： 論證必須依賴的前提（用否定測試法找）
- 充分假設 (Sufficient Assumption)： 能讓論證成立的前提（但不是唯一可能的）
2.4 Paradox 策略
框架：
Fact A: ___ (矛盾的一方)
Fact B: ___ (矛盾的另一方)
Resolution: ___ (引入新因素解釋兩者為何不矛盾)
2.5 Inference 策略
判斷標準：
- Must be true（必須為真）→ 選擇最保守的推論
- Could be true（可能為真）→ 不足以成為答案
- Must be false（必須為假）→ 排除
Section 3：Common Logical Fallacies
了解常見的邏輯謬誤有助於識別論證中的弱點。
| 謬誤名稱 | 英文 | 說明 | 範例 |
|---|---|---|---|
| 因果謬誤 | Post hoc / Correlation-Causation | A在B之前發生，不代表A導致B | 冰淇淋銷量上升時溺水人數也上升，不代表冰淇淋導致溺水 |
| 以偏概全 | Hasty Generalization | 用少數例子推出普遍結論 | 我認識三個X國人都很懶，所以X國人都懶 |
| 滑坡謬誤 | Slippery Slope | 假設A會不可逆地導致極端結果Z | 如果允許學生用手機，他們就不學習，最後社會崩潰 |
| 稻草人謬誤 | Straw Man | 歪曲對方論點再加以反駁 | A說「應該增加教育預算」，B反駁「A想讓軍事預算歸零」 |
| 訴諸權威 | Appeal to Authority | 用權威人物代替證據 | 某明星說這藥有效，所以一定有效 |
| 循環論證 | Circular Reasoning | 結論出現在前提中 | 這本書是對的，因為書裡說它自己是对的 |
| 虛假二分 | False Dilemma | 只給兩個選擇但實際有更多 | 你要麼支持我，要麼反對進步 |
| 生物類比 | False Analogy | 用不恰當的類比來論證 | 公司就像家庭，所以員工不應該要求加薪 |
Section 4：Practice Questions
Strengthen Questions (Q1-Q3)
Question 1: A study of 500 office workers found that those who kept potted plants on their desks reported 30 percent fewer sick days than those who did not. Researchers concluded that the presence of plants improves employees’ immune function.
Which of the following, if true, most strengthens the researchers’ conclusion?
(A) Some office workers are allergic to certain types of plants. (B) Office workers who keep plants on their desks also tend to exercise more regularly and eat healthier diets than those who do not. (C) The plants used in the study release compounds that have been shown in laboratory tests to reduce airborne bacteria and improve air quality. (D) Office workers who take fewer sick days are more likely to receive promotions. (E) The study was conducted over a period of only three months.
Question 2: City X implemented a new traffic law requiring all cyclists to wear helmets. In the year following the law’s implementation, the number of serious head injuries among cyclists in City X decreased by 40 percent.
Which of the following, if true, most strengthens the argument that the helmet law caused the decrease in head injuries?
(A) The number of cyclists in City X remained approximately the same during the period in question. (B) Some cyclists in City X were already wearing helmets before the law was passed. (C) Neighboring City Y, which has no helmet law, saw a 5 percent decrease in cyclist head injuries. (D) The cost of bicycle helmets has decreased in recent years. (E) City X also improved its bike lane infrastructure during the same period.
Question 3: A company replaced its traditional fluorescent office lighting with blue-enriched lighting, which mimics natural daylight. Over the following six months, employee productivity increased by 15 percent, and surveys showed higher job satisfaction.
Which of the following, if true, most strengthens the claim that the lighting change caused the productivity increase?
(A) The company also gave employees a small pay raise during the same period. (B) A control group of employees who continued working under fluorescent lighting showed no productivity increase. (C) Employees initially complained about the new lighting. (D) The company hired several new highly productive employees during the period. (E) Blue-enriched lighting is more energy-efficient than fluorescent lighting.
Weaken Questions (Q4-Q6)
Question 4: A newspaper article reports that Town A, which banned plastic bags in 2020, saw a 25 percent reduction in street litter by 2023. The article concludes that banning plastic bags is an effective way to reduce litter.
Which of the following, if true, most seriously weakens the article’s conclusion?
(A) Some residents of Town A still use plastic bags brought from neighboring towns. (B) Town A simultaneously launched a major public awareness campaign about littering and installed additional public trash bins during the same period. (C) Plastic bags account for only a small percentage of all litter. (D) Several other towns have also banned plastic bags. (E) The fine for littering in Town A was increased in 2021.
Question 5: Researchers found that students who eat breakfast score higher on morning exams than students who skip breakfast. They conclude that eating breakfast improves academic performance.
Which of the following, if true, most weakens this conclusion?
(A) Students who eat breakfast also tend to get more sleep than those who skip it. (B) The exams were administered in multiple subjects. (C) Some students who ate breakfast still performed poorly. (D) The study included students from different grade levels. (E) Breakfast was provided free of charge to all participants.
Question 6: A company found that employees who work from home three days per week complete 20 percent more tasks than those who work entirely in the office. The company concludes that remote work increases productivity.
Which of the following, if true, most weakens this conclusion?
(A) Employees who chose to work from home were already among the most productive before the policy change. (B) The company uses a task-tracking system to measure productivity. (C) Some employees prefer working in the office. (D) The company’s overall revenue increased during the same period. (E) Remote workers report feeling less connected to their colleagues.
Assumption Questions (Q7-Q9)
Question 7: A nutritionist claims that drinking at least eight glasses of water per day leads to better skin health, citing a study in which participants who drank eight or more glasses of water daily reported improved skin moisture levels.
The nutritionist’s claim depends on which of the following assumptions?
(A) All participants in the study had similar skin types. (B) Improved skin moisture is a reliable indicator of overall skin health. (C) Drinking more than eight glasses of water provides no additional benefits. (D) The participants did not use any skincare products during the study. (E) Eight glasses of water is the optimal amount for all body types.
Question 8: A museum director argues that offering free admission on weekends will increase overall revenue because the additional visitors will spend more money at the museum’s gift shop and cafe.
The director’s argument assumes which of the following?
(A) The museum currently charges more than visitors are willing to pay. (B) Free admission will attract visitors who are likely to make purchases at the gift shop and cafe. (C) Weekday attendance will not decrease as a result of the policy. (D) The museum’s operating costs will not increase with more visitors. (E) Other museums that offer free admission have higher revenues.
Question 9: An educator argues that students learn vocabulary more effectively from reading books than from using flashcard apps, because a study showed that students who read extensively had larger vocabularies than those who used flashcard apps.
The educator’s argument requires which of the following assumptions?
(A) Flashcard apps are not an effective way to learn vocabulary. (B) The students in the study were similar in all relevant respects except their vocabulary-learning method. (C) Reading books is more enjoyable than using flashcard apps. (D) Students who use flashcard apps do not also read books. (E) A large vocabulary indicates effective vocabulary learning.
Paradox Questions (Q10-Q12)
Question 10: Country X has a higher average income than Country Y. However, residents of Country Y report higher levels of life satisfaction than residents of Country X.
Which of the following, if true, most helps to resolve this apparent paradox?
(A) Country Y has a more equitable distribution of income than Country X. (B) Country X has a larger population than Country Y. (C) Both countries have universal healthcare systems. (D) Residents of Country X work longer hours than residents of Country Y. (E) The survey was conducted in the local language of each country.
Question 11: A certain species of bird builds its nests exclusively on cliffs overlooking the ocean, even though trees and buildings that could serve as nesting sites are abundant nearby. This behavior seems maladaptive because cliff nests are more exposed to predators and harsh weather.
Which of the following, if true, most helps to explain this behavior?
(A) The birds’ primary food source is fish found in the ocean near the cliffs. (B) Other bird species in the area also nest on cliffs. (C) The birds return to the same nesting sites year after year. (D) Cliff nests provide better visibility for detecting approaching predators. (E) The population of this bird species has been declining in recent years.
Question 12: A pharmaceutical company raised the price of a widely used medication by 300 percent. Surprisingly, the company’s total revenue from the medication decreased after the price increase.
Which of the following, if true, most helps to explain this surprising result?
(A) The medication is also available as a cheaper generic version from other manufacturers. (B) The company spent more on advertising after the price increase. (C) The medication is used to treat a rare condition. (D) The company’s manufacturing costs also increased. (E) Some patients switched to alternative treatments after the price increase.
Inference Questions (Q13-Q15)
Question 13: All employees in the marketing department are required to attend a weekly meeting. Sarah, who works in the marketing department, has not attended a weekly meeting in over a month.
Which of the following can be properly inferred from the information above?
(A) Sarah has been fired from the marketing department. (B) Sarah is the only employee who has missed meetings. (C) Sarah has violated a workplace requirement. (D) The weekly meetings are not important. (E) Sarah’s manager is aware of her absences.
Question 14: In a survey of 1,000 adults, 60 percent said they preferred tea over coffee. Among respondents aged 18 to 30, however, 70 percent said they preferred coffee over tea.
Which of the following can be properly inferred?
(A) Most adults aged 31 and older prefer tea over coffee. (B) Young adults drink more beverages than older adults. (C) Coffee consumption is increasing nationwide. (D) No respondents said they drink neither tea nor coffee. (E) Adults aged 18 to 30 make up less than 50 percent of the survey respondents.
Question 15: A school district found that students who participated in after-school tutoring programs scored an average of 12 points higher on standardized math tests than students who did not participate. However, the tutoring program was optional, and students had to apply to participate.
Which of the following can be properly inferred?
(A) The tutoring program caused the increase in test scores. (B) Students who applied for tutoring were likely already more motivated than those who did not. (C) After-school tutoring is the most effective way to improve math scores. (D) Students who did not participate in tutoring cannot score above average. (E) The school district should make tutoring mandatory.
Answer Key with Detailed Analysis
Q1: Strengthen — Answer: (C)
Analysis: The researchers concluded that plants improve immune function, causing fewer sick days. The gap is: why would plants improve immune function? Option (C) provides a direct mechanism — plants release compounds that reduce bacteria and improve air quality — which bridges the gap between “plants on desk” and “fewer sick days.”
- (A) weakens the argument
- (B) is an alternative explanation (healthier lifestyle), which weakens
- (D) is irrelevant to causation
- (E) raises concerns about study duration
Q2: Strengthen — Answer: (A)
Analysis: The argument is: helmet law → 40% decrease in head injuries. The key assumption is that the number of cyclists did not change dramatically. If the number of cyclists dropped by 40%, the decrease in injuries might simply reflect fewer cyclists, not the helmets. Option (A) eliminates this alternative explanation.
- (B) is irrelevant to the conclusion
- (C) slightly supports but does not strengthen as directly as (A)
- (D) is irrelevant
- (E) provides an alternative explanation, which weakens
Q3: Strengthen — Answer: (B)
Analysis: A control group showing no improvement directly strengthens the causal claim by ruling out other factors (e.g., general economic improvement, seasonal effects).
- (A) and (D) provide alternative explanations, weakening
- (C) is irrelevant to causation
- (E) addresses efficiency, not productivity
Q4: Weaken — Answer: (B)
Analysis: The argument assumes the bag ban caused the litter reduction. Option (B) introduces simultaneous confounding variables (awareness campaign + more trash bins), providing alternative explanations for the litter reduction.
- (A) slightly weakens but less directly
- (C) could weaken but is less specific
- (D) and (E) do not directly address the causation
Q5: Weaken — Answer: (A)
Analysis: The argument assumes breakfast causes better performance. Option (A) introduces “more sleep” as an alternative explanation — perhaps sleep, not breakfast, is the real cause.
- (C) is anecdotal and does not weaken the general trend
- (B), (D), (E) do not provide alternative explanations
Q6: Weaken — Answer: (A)
Analysis: The argument assumes remote work caused higher productivity. Option (A) introduces selection bias — the people who chose remote work were already more productive, so the productivity difference may reflect the workers, not the work arrangement.
- (B) supports measurement reliability
- (C), (D), (E) are irrelevant to causation
Q7: Assumption — Answer: (B)
Analysis: The nutritionist equates “improved skin moisture” with “better skin health.” If skin moisture is NOT a reliable indicator of skin health, the argument collapses. Negation test: “Skin moisture is NOT a reliable indicator of skin health” → argument falls apart.
Q8: Assumption — Answer: (B)
Analysis: The director assumes that visitors who come for free admission will spend money at the gift shop and cafe. If these visitors come only for the free admission and never buy anything, the revenue argument fails. Negation test: “Free-admission visitors are NOT likely to make purchases” → revenue argument collapses.
Q9: Assumption — Answer: (B)
Analysis: The study compares two groups, attributing the vocabulary difference to the learning method. This requires the groups to be comparable. If the extensive readers were already stronger students, the comparison is invalid. Negation test: “The students were NOT similar except for their learning method” → argument fails.
Q10: Paradox — Answer: (A)
Analysis: Paradox: higher income (Country X) but lower satisfaction. Option (A) introduces income distribution — if Country Y’s income is more evenly distributed, residents may feel more financially secure and satisfied despite lower average income.
- (D) provides a partial explanation but is less comprehensive than (A)
Q11: Paradox — Answer: (D)
Analysis: Paradox: cliff nests seem worse (more exposed) but birds choose them. Option (D) explains that cliffs provide better visibility for predator detection, offsetting the seeming disadvantage.
- (A) explains food access but not nest site choice
- (B) and (C) don’t explain why cliff nesting is adaptive
Q12: Paradox — Answer: (E)
Analysis: Paradox: higher price should increase revenue, but revenue decreased. Option (E) explains that patients switched to alternatives, meaning the quantity sold dropped enough to offset the price increase.
- (A) could explain but (E) is more direct
- (B), (C), (D) don’t explain the revenue decrease
Q13: Inference — Answer: (C)
Analysis: All marketing employees must attend → Sarah is in marketing → Sarah has not attended → Sarah has violated the requirement. This is a deductively valid inference.
- (A), (B), (D), (E) go beyond what can be inferred
Q14: Inference — Answer: (E)
Analysis: Overall, 60% prefer tea. But 18-30 group, 70% prefer coffee. If the 18-30 group were the majority (more than 50%), the overall tea preference (60%) would be mathematically unlikely. Therefore, the 18-30 group must be less than 50%.
Q15: Inference — Answer: (B)
Analysis: The program was optional and required application. Students who take the initiative to apply for tutoring are likely more motivated, which is a self-selection effect. This is a reasonable inference from the study design.
- (A) assumes causation without evidence
- (C), (D), (E) go far beyond what can be inferred
邏輯推理要訣
- 永遠先找 Conclusion 和 Premise
- Strengthen → 找 Gap，補上
- Weaken → 找 Assumption，打破
- Assumption → 用否定測試法
- Paradox → 找能同時解釋兩個事實的選項
- Inference → 只選「必須為真」的答案
導航
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