3.4 Inferences
Key Takeaways
- A supported inference must follow from the passage; outside knowledge is not allowed and is a liability.
- Inferences items close the Information and Ideas group, so they are typically the hardest reading items in the first half of a module.
- Beware causal leaps: a correlation in the passage does not support a causal answer.
- Beware over-generalization: one example does not support a universal claim.
- If an answer could be false even when the passage is true, it is not supported.
The Inferences skill asks you to draw a reasonable conclusion from a passage without going beyond what it actually states. It is the last of the four Information and Ideas testing points, and its items sit at the end of that domain group, so they tend to be the hardest reading items in the first half of a module. These items are easy to over-think because the right answer feels almost too obvious and the wrong answers feel plausible in real life.
What an Inference Is (and Isn't)
An inference is a conclusion that follows from the text without requiring outside knowledge. The SAT uses stems like:
| Stem | Meaning |
|---|---|
| "Which choice is most strongly supported by the text?" | The answer must be derivable from the passage. |
| "Which inference is best supported by the passage?" | Same. |
| "Based on the passage, which of the following must be true?" | A stronger version — the answer has to be logically forced. |
| "It can reasonably be inferred from the passage that..." | Standard inference. |
The critical rule: the correct answer requires no outside knowledge. Anything you bring in from outside the passage is a liability, not a help, on these questions.
Strategy: Supported, Required, No Leap
- Read the passage actively — note what is explicitly stated and what is implied.
- For each answer, ask: "Does the text actually say (or necessarily imply) this?"
- Eliminate three categories:
- Over-inference — goes beyond what is stated (generalizes from one case to a rule, projects into the future, assumes causation from correlation).
- Under-inference — restates a detail rather than inferring anything; it is supported but does not answer the inference question.
- Contradiction — directly conflicts with a stated fact.
- The remaining answer is the one the text actually forces.
Three Common Traps
| Trap | Description | Example |
|---|---|---|
| Plausible in real life | True in the world, but not stated in the passage | Passage: "The plant's leaves close at night." Inference: "The plant is responding to light." (could be, but not stated) |
| Over-generalization | Passage shows one instance; answer generalizes to all | Passage: "One species of octopus uses tools." Inference: "Octopuses are tool users." (over-broad) |
| Causal leap | Passage shows correlation; answer assumes causation | Passage: "Cities with more parks have higher reported well-being." Inference: "Parks cause well-being." (causation not established) |
Inference vs Detail vs Unsupported Leap
| Answer type | Description | Verdict |
|---|---|---|
| Detail | Stated verbatim in the passage | Wrong on an inference question (under-inference) |
| Supported inference | Not stated, but the passage's facts force it | Correct |
| Unsupported leap | Plausible, but the passage does not force it | Wrong (over-inference) |
| Contradiction | Conflicts with a passage fact | Wrong |
The key distinction: a supported inference is one where, if the passage is true, the answer must also be true. A plausible leap is one where the answer could be true even if the passage is true, but the passage does not force it.
Worked Example
Passage: "Until the 1980s, the Klamath River's spring-run chinook salmon were assumed to migrate at the same time as their fall-run relatives. Genetic work in 2018, however, showed that spring-run chinook carry a mutation in the GREB1L gene that fall-run fish lack — and that this mutation is absent from all other Pacific salmon species surveyed."
Question: Which choice is most strongly supported by the text?
- A. The GREB1L mutation causes the spring-run chinook's earlier migration. (causal leap — the passage notes the mutation is correlated with the spring run but does not state it causes migration)
- B. Spring-run and fall-run Klamath chinook are genetically identical except for the GREB1L region. (over-claim — the passage only says the mutation differs, not that nothing else does)
- C. The GREB1L mutation found in Klamath spring-run chinook is not found in any other surveyed Pacific salmon species. (correct — directly supported)
- D. Spring-run chinook evolved from fall-run chinook relatively recently. (not stated — requires outside chronology)
C is correct because the passage explicitly states that the mutation is absent from other surveyed Pacific salmon species. A is the classic causal-leap trap: a correlation is presented, and the answer assumes causation. B over-generalizes the genetic finding. D requires outside knowledge of evolutionary timing.
Key Takeaways
- The correct inference must follow from the passage; outside knowledge is not allowed.
- Beware causal leaps: correlation in the passage does not support a causal answer.
- Beware over-generalization: one example does not support a universal claim.
- A verbatim detail is not an inference — it under-infers.
- If the answer could be false even when the passage is true, it is not supported.
Passage: "In 19th-century English textile mills, child laborers who worked near spinning mules developed respiratory illness at roughly three times the rate of children in agricultural parishes with similar overall mortality. Factory inspectors noted that the dust load in the carding rooms often exceeded that of the mines." Which choice is most strongly supported by the text?
Passage: "Many informal settlements on the hillsides above Caracas sit on unstable slopes. After a 1999 landslide in neighboring Vargas state killed an estimated 10,000 to 30,000 people, residents of one such settlement built a network of retaining walls from salvaged concrete and rebar, often without engineering input. Decades later, the walls still stand, and the settlement has not seen a major slope failure." Which inference is best supported by the passage?