Reading: Main Ideas, Details and Relationships Among Ideas · 4 min read
Statements That Strengthen or Weaken an Argument
This chapter also covers Objective 0001. The WEST-B can ask whether a new statement would strengthen or weaken the main idea or argument of a passage. This skill combines reading for the main idea with careful thinking about evidence.
Breaking an Argument into Parts
An argument has a claim (the conclusion the writer wants you to accept) and support (the reasons and evidence offered). Before you can judge whether a new statement helps or hurts, you must state the claim precisely. A vague understanding of the claim leads to wrong choices.
Use this three-step routine for every strengthen or weaken item.
State the writer's claim in one sentence, using the writer's own scope and limits.
Identify the evidence and the link the writer assumes between evidence and claim.
Test each choice: does it make the claim more likely to be true, less likely, or neither?
What Strengthens an Argument
A statement strengthens an argument when it adds new support, confirms an assumption the argument depends on, or rules out another explanation. Strong strengtheners are specific and directly connected to the claim.
A strengthener would confirm that assumption. A statement such as "When a nearby town's library stayed open until nine, evening visits by working adults tripled within a year" gives direct, comparable evidence.
A statement such as "The library recently added new computers" is true-sounding but irrelevant to hours and workers.
Result: The best strengthener supports the assumption that closing time is the barrier, ideally with evidence from a similar situation.
What Weakens an Argument
A statement weakens an argument when it attacks the evidence, breaks the link between evidence and claim, or offers a different explanation for the facts. A weakener does not have to prove the claim false; it only has to make it less likely.
Using the same library passage, a weakener could be: "Most full-time workers in the survey said they avoid the library because parking is unavailable near the building." This offers another reason for low use. If parking is the real problem, longer hours may not help.
Ways to Strengthen or Weaken a Claim
| Move | Strengthens when it... | Weakens when it... |
|---|---|---|
| Evidence | Adds similar, reliable data | Shows the data are flawed or small |
| Assumption | Confirms the hidden link | Shows the link does not hold |
| Alternative cause | Rules out another cause | Offers a more likely cause |
| Comparison | Shows a similar case succeeded | Shows a similar case failed |
Common Trap: Watch for choices that are on the topic but do not touch the claim. A statement about how many books the library owns is about libraries, but it does not affect whether longer hours bring in working adults. Topic overlap is not the same as relevance.
Exam Tip: Read the stem carefully. "Most strengthens," "most weakens," and "least supports" ask different things. Circle the key word on your scratch materials or repeat it to yourself before you read the choices.
Strengthening or Weakening a Main Idea in an Expository Passage
Not every passage is an argument. Some explain or inform. The test can still ask which statement, if added, would best support the passage's main idea. In this case, choose the statement that gives a new example or fact of the same kind the passage uses, aimed at the same point.
Mini-Passage: Coastal wetlands act as natural flood barriers. Their grasses slow incoming waves, and their soils soak up water like a sponge. After a severe storm, communities behind healthy marshes often report less flooding than nearby communities whose marshes were filled in for development.
A statement that would support this main idea: "Engineers estimate that a mile of healthy marsh can reduce the height of a storm surge by several inches." A statement that would weaken it: "In the last storm, a town with an intact marsh flooded more than a nearby town without one, because the marsh town sits much lower." Notice that even this weakener is limited; it introduces a confounding factor, elevation, rather than disproving the claim outright.
Memory Aid: Strengtheners build a bridge between evidence and claim. Weakeners knock out a support beam or show a second road to the same place.
Key Takeaways
Before testing choices, restate the claim precisely, including its limits.
Strengtheners add evidence, confirm an assumption or rule out alternatives.
Weakeners attack evidence, break the assumed link or offer a different cause.
A choice on the same topic is not automatically relevant to the claim.
Read the stem's key word (strengthen, weaken, least) before evaluating choices.
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