Strengthening and Weakening Arguments

The Four-Step Process

First identify the conclusion, then the evidence, then the gap -- the assumption connecting them. The best strengthener bridges that gap; the best weakener widens it. Strengtheners add supporting data, eliminate alternative explanations, or reinforce an assumption. Weakeners contradict the data, introduce rival explanations, or undermine an assumption.

The Classic Example

Argument: "City X reduced crime by installing streetlights." Strengthener: similar cities that did not install lights saw no crime drop -- this eliminates alternatives. Weakener: City X also hired 200 police officers in the same period -- a rival explanation for the same result.

Ranking, Not Spotting

CARS rarely offers one relevant choice among three irrelevant ones; it offers several plausible choices and asks for the MOST strengthening or damaging. Rank by how directly each option hits the argument's central assumption: a choice attacking the core causal link beats one nibbling at a side detail. Note that a weakener need not disprove the conclusion -- it only needs to make it less likely.

Key Takeaways

• Find conclusion, evidence, and the gap between them first
• Best strengthener: rules out alternative explanations
• Best weakener: supplies a rival explanation or breaks the causal link
• Rank all plausible choices -- "most" is the operative word