Chapter 1: Key Ideas and Details
Key Ideas and Details is the largest content category on the Reading test, tied with Integration of Knowledge and Ideas. It asks one core question in three forms: can you state what a passage says? You will identify the main idea and primary purpose, track the supporting ideas and specific details, and draw the small, safe conclusions the text justifies. Every answer is verifiable in the passage. No outside knowledge is ever required, and outside knowledge is the single most common source of wrong answers.
17 to 22
questions from this category
35%
of the examination
3
tested skills: main idea, support, inference
Learning Outcomes
After studying this lesson, you will be able to:
- Identify accurate summaries or paraphrases of the main idea or primary purpose of a reading selection.
- Identify accurate summaries or paraphrases of the supporting ideas and specific details in a reading selection.
- Identify inferences and implications that can reasonably be drawn from the directly stated content of a reading selection.
(1) MAIN IDEA AND PRIMARY PURPOSE
Every passage is built on one controlling point. Main idea questions ask you to recognize that point when it is restated in different words, and purpose questions ask you to recognize why the author wrote the passage at all. The two are related but not identical, and the exam tests both.
(A) Topic, Main Idea, and Detail: Three Levels, Not One
Confusing these three levels is the root cause of most wrong answers in this category, so separate them first.
| Level | What it is | Example |
|---|---|---|
| Topic | The subject, expressed as a word or phrase. It makes no claim. | Urban street trees |
| Main idea | The topic plus the author's point about it, expressed as a complete claim. | Street trees deliver measurable public benefits and deserve infrastructure funding. |
| Detail | A single fact, example, or statistic that supports the main idea. | Tree canopies lower summer street temperatures. |
Apply the replacement test: the correct main idea option is the one sentence that could stand in for the entire passage. A topic cannot replace the passage because it claims nothing. A detail cannot replace the passage because it covers only part of it.
(B) Stated and Implied Main Ideas
- A stated main idea appears in a single sentence of the passage, most often the first or last sentence. The sentence that states it is the topic sentence.
- An implied main idea is never written out. You derive it by asking what all the details, taken together, add up to demonstrate.
- To find an implied main idea, list what each sentence contributes, then complete this frame: "All of these sentences combine to show that ______." The completed sentence is the main idea.
On the Exam: Short passages and brief statements often bury the controlling claim mid-passage or imply it entirely. Never select an option just because it echoes the first sentence. Confirm that the rest of the passage actually develops that sentence.
(C) Primary Purpose: The Author's Reason for Writing
The primary purpose is what the author is trying to accomplish, and purpose options almost always begin with the word "to" followed by a verb. Evaluate the verb before you evaluate anything else. If the verb is wrong, the option is wrong, no matter how accurate the rest of it sounds.
| Purpose verb family | The author is trying to... | Signals in the passage |
|---|---|---|
| inform / explain / describe | present facts or clarify how something works | neutral tone, definitions, statistics, process steps |
| persuade / argue / advocate | convince you to accept a position or take an action | evaluative words (should, must, best), counterargument handling |
| compare / contrast | weigh two subjects against each other | both, unlike, whereas, on the other hand |
| entertain / narrate | tell a story or create an experience | characters, chronology, sensory language |
| critique / question | evaluate or cast doubt on a claim, work, or practice | concessions followed by objections, however, yet |
On the Exam: Purpose options also fail on scope. "To explain how vaccines are tested" and "to explain the history of medicine" may share a verb, but only one matches what the passage actually covers. Check the verb first, then check that the object of the verb is neither broader nor narrower than the passage.
(D) What Makes a Summary or Paraphrase Accurate
The exam statement is precise: you must identify accurate summaries or paraphrases. These are two different rewrites, and both must pass the same accuracy tests.
Summary
- Condenses the whole selection to its essential point
- Much shorter than the original
- Keeps the main idea, drops minor details
- Fails if it captures only one section of the passage
Paraphrase
- Restates a specific portion in different words
- Roughly the same length as the original
- Keeps all the meaning, changes the wording
- Fails if it shifts emphasis, certainty, or attitude
An accurate rewrite of either kind must pass all four checks:
- Complete: it covers the point being restated, not a fragment of it.
- Faithful: it adds no information the passage does not contain.
- Proportional: it preserves the author's emphasis rather than promoting a side comment.
- Neutral: it keeps the author's degree of certainty. "Suggests" must not become "proves."
⚠ COMMON TRAP: The four wrong-answer patterns for main idea questions are stable across the entire exam. Learn to name them: too broad (claims more than the passage covers), too narrow (promotes one detail to headline status), distortion (uses the passage's own words but changes the claim), and extreme upgrade (turns "associated with" into "causes" or "suggests" into "proves"). Naming the flaw is faster and more reliable than judging whether an option "sounds right."
Worked Example 1: Main Idea
City planners have long treated street trees as decoration, but a growing body of research suggests they are infrastructure. Mature canopies lower summer street temperatures by several degrees, reducing heat-related illness in neighborhoods with little shade. Trees absorb stormwater that would otherwise strain aging drainage systems. Several large studies also associate tree-lined blocks with lower rates of asthma and stress. Cities that budget for trees only as beautification, researchers argue, are undervaluing one of their most cost-effective public assets.
Which of the following best summarizes the main idea of the passage?
- Mature tree canopies lower summer street temperatures in neighborhoods that lack shade.
- Research indicates that street trees provide measurable public benefits and should be valued as infrastructure rather than decoration.
- Cities must expand every form of green space to protect residents' physical and mental health.
- Researchers have proven that living on a tree-lined block prevents asthma.
Option A restates one supporting detail, the cooling effect, so it is NOT the best answer: it is too narrow.
Option C expands the claim from street trees to every form of green space, so it is NOT the best answer: it is too broad.
Option D upgrades "associate" to "proven" and "prevents," so it is NOT the best answer: it is an extreme upgrade of the passage's certainty.
Option B captures the claim every sentence develops, trees deliver benefits that justify infrastructure status, and preserves the passage's cautious verbs, so it IS the best answer.
(2) SUPPORTING IDEAS
Supporting ideas answer the question "How does the author back that up?" Detail questions are the most literal items on the test: the answer is stated in the passage, and your job is to find it and recognize it in reworded form. Precision, not interpretation, is the skill being measured.
(A) The Support Hierarchy
Passages are layered. Seeing the layers tells you instantly whether an option describes the main idea, a major support, or a minor detail, and detail questions frequently swap these levels to build distractors.
the claim the whole passage exists to make
the reasons, findings, or claims that directly back the main idea
the statistics, examples, and specifics that back each major idea
| Type of support | Signal words |
|---|---|
| Examples | for example, for instance, such as |
| Facts and statistics | numbers, percentages, dates, measured amounts |
| Reasons and causes | because, since, as a result, therefore |
| Expert testimony | according to, researchers found, officials report |
| Sequence or process | first, next, then, finally |
(B) The Locate-and-Verify Method
Stems that begin "According to the passage..." or "The passage states..." announce that the answer is directly stated. Use a fixed four-step routine:
- Mark the key words in the question stem (the specific noun, number, or condition it asks about).
- Locate the sentence or two in the passage containing those key words or their synonyms. The answer to a detail question lives in one or two sentences, never everywhere.
- Read the located sentence precisely, including its qualifiers: only, most, some, unless, except.
- Verify the option against the sentence, matching meaning rather than wording.
On the Exam: Correct detail answers are usually paraphrases: same meaning, new words. Wrong answers frequently do the reverse, reusing the passage's exact words while quietly changing the claim. Word-matching is the trap; meaning-matching is the skill.
(C) How Detail Distractors Are Built
Wrong options on detail questions are engineered from a short list of predictable edits to the passage's stated content. Recognize the edit and you can eliminate the option without hesitation.
| Distractor pattern | What it does to the stated detail |
|---|---|
| Scope narrowing | Adds "only" or "solely" to a statement the passage makes broadly |
| Scope broadening | Deletes a qualifier, turning "some" or "in most cases" into "all" or "always" |
| Role swap | Assigns an action or result to the wrong person, group, or thing |
| Condition confusion | Reads a conditional statement as absolute, or an absolute as conditional |
| Outside knowledge | States something true in the real world that the passage never says |
⚠ COMMON TRAP: A detail can be accurately restated and still be the wrong answer because it is not the detail the question asked about. After verifying that an option matches the passage, verify that it also answers the stem. "True but unresponsive" options catch test takers who stop checking as soon as they confirm a statement appears in the text.
Worked Example 2: Supporting Detail
The city's new curbside composting program accepts food scraps, coffee grounds, and soiled paper products such as napkins and pizza boxes. Residents receive a sealed countertop bin and a larger wheeled cart, which crews empty every Tuesday alongside regular trash collection. Plastic bags, including those labeled biodegradable, are not accepted because they contaminate the finished compost. In its first six months, the program diverted roughly 4,000 tons of waste from the county landfill.
According to the passage, why are plastic bags excluded from the composting program?
- They take far longer to break down than food scraps do.
- They contaminate the finished compost.
- Collection crews are unable to pick them up on Tuesdays.
- They are excluded only when they are not labeled biodegradable.
Option A is plausible from real-world knowledge, but the passage never gives decomposition time as the reason, so it is NOT the best answer: outside knowledge.
Option C attaches the exclusion to the collection schedule, which the passage mentions in a different sentence for a different purpose, so it is NOT the best answer: role swap.
Option D reverses the stated condition: the passage excludes plastic bags including biodegradable-labeled ones, so it is NOT the best answer: condition confusion.
Option B restates the passage's stated reason, contamination of the finished compost, so it IS the best answer.
(3) INFERENCES
An inference is a conclusion the passage supports but never states outright. The exam statement carries a built-in limit that most test takers miss: inferences must be drawn from the directly stated content of the selection. You are not being asked to speculate. You are being asked to take the smallest logical step the stated evidence forces.
(A) The Anchor Rule
Every correct inference is anchored: you can point to the specific stated sentence or sentences that justify it. If you cannot point to the anchor, you are guessing, not inferring.
Stated content + one small logical step = reasonable inference
Stated content + real-world assumptions + a big leap = wrong answer
Recognize inference stems by their signal verbs: implies, suggests, can be inferred, can be concluded, most likely. When you see one, your standard shifts from "Is this stated?" to "Is this forced by what is stated?"
(B) The Two-Part Test for Any Inference Option
- Anchor check: Which stated sentence supports this option? If no sentence does, eliminate it, even if it is true in the real world.
- Distance check: Is this the smallest step beyond the stated content, or does it require additional assumptions? Predictions about the future, claims about motives never hinted at, and judgments of better or worse usually fail this check.
| Language of safe inferences | Language of overreach |
|---|---|
| some, may, can, at least one, likely, tends to | all, none, always, never, only, must, proves, guarantees |
Cautious wording is not automatically correct and absolute wording is not automatically wrong, but the pattern is strong enough to guide your first eliminations: modest claims are easier for a short passage to support than sweeping ones.
(C) How Inference Distractors Fail
| Distractor pattern | Why it fails |
|---|---|
| Real-world true | Accurate outside the passage, but no stated sentence supports it |
| Extreme claim | Stretches modest stated evidence into always, never, or only |
| Opposite | Contradicts a stated sentence; tempting when the passage contains a contrast |
| Long leap | Predicts outcomes or assigns motives that need assumptions the text never provides |
⚠ COMMON TRAP: The most seductive wrong answer on an inference question is a statement you know to be true. The question is never whether the option is true; it is whether this passage's stated content supports it. Before selecting any inference option, name its anchor sentence. No anchor, no answer.
Worked Example 3: Inference from a Brief Statement
Although the museum extended its evening hours last spring, weekday attendance has continued to decline.
Which of the following can reasonably be inferred from the statement?
- The museum expected the extended evening hours to help attendance.
- Weekend attendance at the museum has increased.
- The museum will soon return to its original hours.
- Visitors dislike attending museum events in the evening.
Option B concerns weekends, which the statement never mentions, so it is NOT the best answer: no anchor.
Option C predicts a future decision the statement gives no basis for, so it is NOT the best answer: long leap.
Option D converts one fact about attendance into a claim about visitor preferences, so it is NOT the best answer: long leap beyond the stated content.
Option A is anchored in the word "Although," which signals that the extended hours and the decline point in opposite directions; that contrast only makes sense if the hours were expected to help. It IS the best answer, and it is the smallest step the stated content forces.
Quick Reference Card: Key Ideas and Details
- Three levels: topic (a phrase, no claim) → main idea (topic + the author's point) → detail (one supporting fact)
- Replacement test: the correct main idea option is the one sentence that could replace the whole passage
- Main idea distractors: too broad · too narrow · distortion · extreme upgrade (suggests ≠ proves)
- Primary purpose: judge the verb first (inform · persuade · compare · narrate · critique), then check scope
- Summary condenses the whole selection; paraphrase restates one portion at similar length; both must add nothing and keep the author's certainty
- Detail questions: locate → read qualifiers → match meaning, not wording (correct answers paraphrase; traps reuse exact words)
- Detail distractors: only added (narrowing) · all/always added (broadening) · role swap · condition confusion · outside knowledge
- Inference = anchor sentence + smallest step; true in the real world but unstated = wrong; extreme words (always · never · only · must) signal overreach