3.2 Command of Evidence: Textual
Key Takeaways
- Command of Evidence is officially split into Textual and Quantitative sub-points; this section covers the textual half.
- Two flavors: choose the finding that supports or the finding that undermines a stated claim.
- The phrase "if true" means you must accept the finding as true and judge only its logical force against the claim.
- Paraphrase the claim, predict the kind of evidence needed, then match — never skip the prediction step.
- Weakening requires the finding to actually contradict the claim at its stated strength, not merely nibble at it.
Command of Evidence is the second skill/knowledge testing point in Information and Ideas, and College Board splits it into two named sub-points: Textual and Quantitative. This section covers the textual half. You are given a short passage that states a claim or hypothesis, and you must choose the evidence from a list that either supports or undermines that claim. Unlike the quantitative version, the evidence here is textual — a sentence or short passage that describes a finding, observation, or result.
Two Question Flavors
- Support/undermine a claim already in the passage. The passage presents a researcher's hypothesis or conclusion; you choose the finding that, if true, most strengthens or most weakens it.
- Match the claim to the evidence. A less common variant gives you the evidence first and asks which claim it best supports.
How the SAT Phrases These Questions
| Stem | What it asks |
|---|---|
| "Which finding, if true, would most directly support the researchers' conclusion?" | Strengthen |
| "Which finding, if true, would most undermine the hypothesis?" | Weaken |
| "Which choice describes a finding that would support the claim that..." | Strengthen |
| "Which result, if observed, would most weaken the argument that..." | Weaken |
| "Which choice provides the best evidence for the conclusion that..." | Strengthen |
The phrase "if true" is important: you must accept the finding as true. Your job is not to judge whether the finding is plausible, only whether, if it occurred, it would help or hurt the claim.
Strategy: Paraphrase, Predict, Match
- Paraphrase the claim in your own words. Strip away the passage's specific nouns and restate the logic. If a passage says "the brighter a firefly's flash, the more attractive it is to mates," the claim is "flash brightness correlates with mating success."
- Predict the kind of evidence needed. To support a correlation claim, you would expect data showing brighter-flash individuals mate more. To undermine it, you would expect data showing brightness has no effect or the opposite effect.
- Match against the choices. Look for the choice that most directly bears on the predicted relationship. Reject evidence that bears on a different relationship.
This three-step process matters because the wrong-answer traps are built around skipping step 2. Without a prediction, you will be drawn to an answer that "feels scientific" without actually testing the claim.
The Two Big Traps
Trap 1: True but irrelevant. A choice states a real finding that has nothing to do with the claim's specific logic. It sounds relevant because it shares vocabulary with the passage, but it tests a different variable.
Trap 2: Supports a different claim. A choice does strengthen a claim — just not the one the passage makes. If the passage claims "compound X kills bacteria by disrupting cell walls," an answer showing "compound X also kills fungi" is interesting but does not support the mechanism claim being tested.
For weaken questions, the trap is a finding that shows the claim is imperfect but does not actually contradict it. A claim that "X causes Y" is not weakened by showing "X sometimes does not cause Y" unless the claim was "X always causes Y." Read the strength of the claim carefully.
Worked Example
Passage: "Biologist Nalini Nadkarni hypothesized that arboreal mosses in the Olympic rainforest depend on fog rather than rain as their primary water source, because fog persists during the dry summer months when rain is absent."
Question: Which finding, if true, would most directly support Nadkarni's hypothesis?
- A. Olympic rainforest mosses can survive for weeks without any water. (interesting but does not address the source of water)
- B. Mosses growing on Olympic trees contain higher concentrations of fog-derived hydrogen isotopes than rain-derived ones. (correct — directly links their tissue to fog water)
- C. The Olympic rainforest receives more total annual precipitation than nearby forests. (irrelevant to which source the mosses use)
- D. Some moss species in the Olympic rainforest also grow in non-foggy forests. (does not address this population's water source)
B is correct because it provides direct isotopic evidence that the mosses incorporate fog water. The other choices describe true facts but none bear on the specific claim about water source.
Support vs Weaken: A Quick Reference
| If the claim is... | To support, look for... | To weaken, look for... |
|---|---|---|
| "X causes Y" | data where X→Y holds | data where X is present but Y is absent, or Y is present without X |
| "X is the main cause of Y" | data showing X dominates other factors | data showing another factor explains most of Y |
| "X benefits from Z" | data where X with Z outperforms X alone | data where X with Z performs the same or worse than X alone |
| "Method M measures P accurately" | data where M matches a known standard for P | data where M diverges from the standard |
Key Takeaways
- Paraphrase the claim before reading the choices.
- Predict the evidence type before matching.
- "If true" means accept the finding and test only its logical force.
- Reject true-but-irrelevant and supports-a-different-claim answers.
- Weakening requires that the finding actually contradicts the claim at its stated strength.
Passage: "Researchers studying the Allolobophora earthworm hypothesized that its deep burrowing in winter is driven not by temperature but by soil moisture: the worms descend to escape waterlogged surface soil." Which finding, if true, would most directly support the researchers' hypothesis?
Passage: "A nutritionist claims that a new prebiotic supplement improves gut health because, in a trial, participants who took the supplement for eight weeks reported less bloating than those who took a placebo." Which finding, if true, would most weaken the nutritionist's conclusion?