Lập luận ngôn từ: giả định, nguyên nhân thay thế và hướng dẫn chứng
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| alternative cause/ɔːlˈtɜːnətɪv kɔːz/ | A different explanation that could produce the same observed result. |
| negation/nɪˈɡeɪʃn/ | The statement that something is not the case. |
The hidden gap in an argument
- "Since the town installed brighter streetlights, reported burglaries fell by 30%. Therefore, the lights reduced crime."
- GRE argument questions ask you to find the assumption, or the evidence that would strengthen or weaken the conclusion.
Observation, assumption, conclusion
- Observation: burglaries fell after the lights went in. Conclusion: the lights caused the fall.
- Assumptions: no other cause (more police, a change in reporting) explains the drop; the fall is not just a normal fluctuation.
Alternative causes 其他原因
- Causal conclusions are weakened by another explanation: "That same year, the town doubled its police patrols."
- They are strengthened by ruling one out: "Patrol numbers stayed the same" or by a comparison: "Neighbouring towns without new lights saw no fall."
Negation 否定 test: an assumption is necessary if its negation destroys the argument. "The reporting method did not change." Negate: "The reporting method changed so fewer burglaries were recorded" — the conclusion collapses, so it is a necessary assumption.
Argument: brighter streetlights caused the 30% fall in burglaries. Which most weakens it?
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An alternative cause for the fall.
Which most strengthens the same argument?
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A comparison group without the change supports the causal link.
Which is a necessary assumption of the argument?
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Negating it destroys the argument.
To test whether an assumption is necessary, imagine its ____.
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If the negation breaks the argument, it is necessary.
Evidence direction
- Ask whether new information makes the conclusion more or less likely — not whether it is interesting or related.
- "Residents like the brighter streets" is relevant to the lights but does nothing for the crime claim.
Strengthen, weaken or neither?
Judge evidence direction for a causal argument.
Information related to the topic always strengthens or weakens the argument.
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It must affect the conclusion's likelihood.
Common traps
- Choosing information on the topic that does not affect the conclusion.
- Confusing a sufficient assumption with a necessary one; use the negation test.
Recap
- Separate observation, assumption and conclusion; look for alternative causes.
- Strengthen by ruling them out; weaken by supplying them; test assumptions by negation.
- alternative cause: A different explanation that could produce the same observed result.
- negation: The statement that something is not the case.