ACT Science — two explanations for one observation

One passage on the ACT Science section contains no data at all. Two scientists are given the same observation and explain it differently, and every question is about the shape of the disagreement rather than about who is right. Nobody is right: the writer has no view, and neither should the reader.

Ten questions on two invented disputes — beetles declining at a ridge where an invasive fern has arrived and summers have warmed, and moss declining in caverns since lamps were installed. Both positions appear in full inside every question, so nothing depends on anything outside it. Both are genuinely reasonable, neither contradicts the observation, and neither is a straw man, because a dispute in which one side is obviously foolish teaches nothing.

Two questions ask what one scientist alone claims, and their most tempting wrong option is always the other scientist's mechanism stated correctly — somebody's position, just not that one.

Two ask what the scientists agree about, and the answer is the observation itself both times. That is nearly always where agreement lies in a passage of this kind: the measurement comes before either of them speaks, and neither is disputing it.

Two ask what divides them, and both require narrowing. In the cavern dispute, both scientists blame the lamps; what separates them is the light acting on the moss's daily rhythm against the heat those same lamps give off. A question asking merely whether the lamps are to blame gets the same answer twice and cannot be the dispute.

Two present a new finding and ask what it does. Neither finding settles anything, and that is deliberate: beetles fall by 15 percent where no fern grows against 40 percent where it does, and moss still falls by 10 percent with the temperature held fixed against 25 without. Each shifts weight to one scientist while leaving the other a share of the effect, and the options separate strengthening a position from refuting it.

The last two ask what one scientist would say about the other's mechanism, and both are keyed to the least their position requires. A scientist who blames the light need not deny that lamps get warm; the option that has her denying it sounds loyal and says more than she does.

Twelve flashcards carry the method, including the habit that answers most of these questions: answer for a scientist by adding nothing they did not say.

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• Separate a shared observation from the competing explanations offered for it
• Attribute each claim to the scientist who actually makes it
• Find the single question two scientists would answer differently, by narrowing past what they share
• Judge what a new finding does to each position in turn, and tell strengthening from refuting
• Notice when a finding leaves the weakened position a share of the effect rather than none
• Answer on a scientist's behalf using only their stated reasoning
• Reject an option that overstates a scientist's claim, even when it sounds like that scientist

Written for the conflicting-viewpoints strand of the ACT science section, following the skills the test's own published description names: understanding and comparing alternative explanations of the same phenomenon, identifying points of agreement and disagreement, and determining how new information affects each hypothesis. Both disputes are invented for this material, along with every scientist, site, species and measurement, and neither is modeled on a real scientific controversy — so no question can be answered from prior knowledge instead of from the text. Both positions are stated in full inside every question. Nothing is taken from any ACT publication or released test.