How to solve SAT inference questions

Inference questions give you a short passage that ends with a blank and ask which choice "most logically completes the text." The passage lays out facts, findings, or arguments, and you supply the conclusion they point to. The skill belongs to the Information and Ideas domain, about 26% of the Reading and Writing section, or roughly 12 to 14 questions shared among three skills, so expect a few inference questions per test. They often feel like the hardest questions in that domain because the passage never states the answer outright.

What the questions look like

Every inference question uses the same stem, but the passages tend to follow one of three patterns.

• Finding to conclusion. Researchers observe something, and the last sentence begins with words like "This suggests that" or "Therefore, the researchers concluded that." You supply the conclusion.
• Ruling out an explanation. The passage offers two possible explanations, then gives evidence that fits only one of them. The blank asks what the evidence implies.
• Exception to a pattern. The passage states a general pattern and then describes a case that breaks it. The blank asks what the exception tells you.

Step-by-step method

1. Read the entire passage, and pay close attention to the words just before the blank. "Therefore" asks for a conclusion, "however" asks for a contrast, and "if so" asks for a consequence.
2. List the premises in plain words. For the first example below, that would be "snail lakes connect to streams, the other lakes don't, and snail eggs die in air."
3. Predict the conclusion before you read the choices. It should follow from the premises without any new facts.
4. Choose the option that matches your prediction most closely. The right answer is often modest, using words like "may" or "likely," because it claims only what the evidence shows.
5. Cross out choices that need an extra assumption, claim more than the passage supports, or contradict a detail.

Worked example

In one mountain range, a species of small freshwater snail lives in some lakes but is absent from others nearby that have similar depth, temperature, and water chemistry. Ecologist Ruth Abara noticed that every lake containing the snail is connected to a stream system, while none of the lakes without the snail are. Because the snail's eggs die within minutes of being exposed to air, Abara concluded that ______

Which choice most logically completes the text?

A) the snail most likely reached the lakes it lives in by moving through connected waterways.
B) the snail would thrive in the isolated lakes if people introduced it there.
C) birds are the snail's main predator in the stream systems.
D) the isolated lakes are too cold for the snail to survive.

Answer: A. The premises are that the snail lakes are connected to streams, the isolated lakes lack the snail, and the eggs can't survive a trip through the air. The conclusion that follows is that the snail spread through water. Choice B goes too far. Similar conditions make survival plausible, but the passage gives no evidence that the snail would thrive. Choice C brings in predators, which the passage never mentions. Choice D contradicts the passage, which says the lakes have similar temperatures.

Here is a ruling-out example.

Moths of one species are darker in the northern part of their range than in the southern part. One explanation holds that dark coloring helps the moths absorb heat in cooler climates. Another holds that it helps them hide on the dark tree bark common in northern forests. Researchers studying a northern forest where the trees have unusually pale bark found that the moths there are just as dark as moths in other northern forests. This finding suggests that ______

Which choice most logically completes the text?

A) moths moved from southern forests to northern forests would soon become darker.
B) the moths' dark coloring is more likely related to climate than to the color of the bark they rest on.
C) pale bark is more common in southern forests than in northern forests.
D) dark coloring gives the moths no advantage in northern forests.

Answer: B. If camouflage explained the dark color, moths in a pale-bark forest should be lighter. They aren't, which weakens the camouflage explanation and leaves the heat explanation as the better fit. B says exactly that, with the cautious "more likely." Choice A predicts a change in individual moths that the passage gives no basis for. Choice C may sound reasonable, but the passage never says it. Choice D is too strong, since the heat explanation is still standing.

Common traps

• Overreach. Words like "proves," "will," "all," and "no advantage" claim more than a short passage can support. Prefer the choice that says only what the evidence allows.
• True in real life, absent from the text. A choice can sound like common knowledge and still be wrong because nothing in the passage leads to it.
• Ignoring a qualifier. Small details like "similar temperature" are there to eliminate choices. Reread the passage for details that contradict each remaining option.
• Off-track conclusions. Some choices relate to the topic but don't continue the logic of the sentence with the blank. The answer has to finish the argument the passage is making.
• Reversed cause and effect. If the passage says A leads to B, a choice saying B leads to A is wrong even though it uses the same terms.

Quick check

Reread the passage with your answer in the blank. The last sentence should follow from what came before without any new facts. If you have to add "and also assume that..." to make it work, pick again.