SAT Reading and Writing: Central Ideas and Details

Type 1: Central Ideas (Main Idea) Questions

What they ask: "What is the main idea of the text?" or "Which choice best states the main purpose of the passage?"

What you need to do: Identify the passage's overarching message—the single most important point the author wants readers to understand.

Common Question Phrasings:

• "Which choice best states the main idea of the text?"
• "The text primarily focuses on which of the following?"
• "What is the main purpose of the passage?"
• "The author's central claim is that..."

Type 2: Details Questions

What they ask: Questions about specific information, facts, or examples mentioned in the passage.

What you need to do: Locate and accurately recall or interpret a specific detail from the text.

Common Question Phrasings:

• "According to the text, what did [X] do?"
• "The passage indicates that [phenomenon] is caused by..."
• "Which detail from the passage supports [claim]?"
• "The author mentions [X] in order to..."

Main Idea = Topic + So What?

Step 1: Read Actively, Not Passively

Don't just let your eyes scan words. Engage with the text by mentally summarizing each paragraph in 3-5 words. This keeps you focused on the "big picture" rather than getting lost in details.

Example mental note: "Paragraph 1: Introduces forest fires | Paragraph 2: Explains natural benefits | Paragraph 3: Argues we need controlled burns"

Step 2: Pay Special Attention to Openings and Closings

Authors often state or strongly hint at the main idea in the first sentence or first paragraph. They frequently restate or emphasize it in the last sentence or paragraph. These are your "main idea hotspots."

• Opening: Often sets up the topic and thesis
• Middle: Provides supporting details and development
• Closing: Reinforces the main point or offers final insight

Step 3: State the Main Idea in Your Own Words BEFORE Looking at Answers

After reading, pause for 5 seconds and think: "If I had to tell someone what this passage is about in ONE sentence, what would I say?" This prediction helps you avoid being swayed by trap answers.

Pro Tip: Your prediction doesn't need perfect wording—it just needs to capture the essence. Then find the answer choice that matches your prediction's meaning.

Step 4: Eliminate Wrong Answers Using "Too Broad" and "Too Narrow" Tests

Wrong answers typically fall into two categories:

• Too Broad: Covers more than what the passage discusses ("all animals" when passage only discusses "honeybees")
• Too Narrow: Focuses on a supporting detail rather than the overall message ("bees pollinate flowers" when the main idea is "declining bee populations threaten agriculture")

The correct main idea is "just right"—it covers exactly what the passage addresses, no more, no less.

Step 5: Verify with the "All Paragraphs Test"

A true main idea should connect to all or most of the passage's paragraphs. If an answer choice only relates to one paragraph, it's probably a supporting detail, not the main idea.

Ask: "Does this answer explain what the ENTIRE passage is about, or just part of it?"

Trap 1: The "Half-Right, Half-Wrong" Answer

This answer starts strong—mentioning something the passage discusses—but then adds incorrect information or goes off track. Every part of the answer must be accurate.

Example: If passage says "Some scientists support theory X," wrong answer might say "Scientists unanimously agree on theory X"

Trap 2: The "True But Irrelevant" Detail

Something mentioned in the passage but not the central focus. These trap answers are factually accurate but don't capture the main idea. They're supporting details masquerading as main ideas.

Trap 3: The "Close Synonym" Confusion

Uses similar-sounding words but subtly changes the meaning. If the passage says "some evidence suggests," the wrong answer might say "proven conclusively" or "definitely shows."

Trap 4: The "Extreme Language" Red Flag

Watch for absolutes like "always," "never," "all," "none," "only," "completely." SAT passages rarely make such extreme claims. If you see these words, double-check that the passage truly supports such strong language.

Trap 5: The "Outside Knowledge" Temptation

An answer might be true in real life but not stated or implied in the passage. Stick to what the text actually says—don't bring in your own knowledge about the topic.

Passage:

The ancient Roman aqueduct system represents one of humanity's most impressive engineering achievements. While many associate aqueducts solely with transporting water across valleys using elevated stone arches, the majority of these structures actually ran underground through carefully constructed channels. Roman engineers calculated precise gradients—typically dropping just 1 foot per 1,000 feet—to maintain steady water flow from mountain sources to urban centers, sometimes covering distances exceeding 50 miles. This mastery of hydraulics enabled Roman cities to support populations far larger than their local water sources could sustain. Beyond serving basic needs, the abundant water supply made possible public baths, fountains, and sanitation systems that dramatically improved urban life. The aqueduct system thus became a cornerstone of Roman civilization, demonstrating how advanced infrastructure can transform society.

Question:

Which choice best states the main idea of the text?

Step-by-Step Solution:

Correct Answer: B

💡 Key Takeaway: The main idea must be comprehensive enough to cover the passage's full scope while remaining specific to what the passage actually discusses. Options A, C, and D all describe things IN the passage, but only B describes what the passage is ABOUT.

Passage:

Echolocation allows dolphins to navigate and hunt in murky water where vision is limited. By emitting high-frequency clicks and interpreting the returning echoes, dolphins can determine an object's size, shape, distance, and even internal structure. This biological sonar is so precise that dolphins can distinguish between different types of metal and identify hollow objects. Scientists have discovered that dolphins can echolocate prey buried under several inches of sand, a capability that far exceeds human-made sonar technology.

Question:

According to the text, what is one thing dolphins can do using echolocation?

Quick Analysis:

Strategy: This is a details question asking for something explicitly stated. Scan for each answer choice in the passage.

Answer: B

This is directly stated in the final sentence. Options A, C, and D might be true about dolphins in general, but they're not mentioned in THIS passage. Always stick to what the text explicitly says.

Adapted from Zora Neale Hurston's "Their Eyes Were Watching God" (1937). Janie has returned to her hometown after a long absence.

The people sat watching her from their porches, their tongues cocked and loaded, waiting for her to come within range. They'd been curious about her for years, and now that she'd returned without her husband, their speculation intensified. But Janie walked past them all, her head held high, caring nothing for their judgmental stares. She'd lived her life, made her choices, and felt no need to explain herself to those who'd never understood her dreams. Their whispers couldn't touch her anymore—she'd found something more valuable than their approval.

Question:

Which choice best states the main idea of the text?

Answer: C

Explanation: The passage establishes a contrast: townspeople judging vs. Janie's indifference to their judgment. Option C captures this central dynamic and explains WHY Janie is unbothered (she values her experiences over their approval). Option A states a fact but misses the main point. Option B focuses only on the townspeople's perspective, not Janie's response. Option D describes an action but not the underlying meaning. The main idea here is about Janie's attitude and independence, which Option C best expresses.

Researchers studying antibiotic resistance have identified a concerning trend: bacteria are evolving defensive mechanisms faster than pharmaceutical companies can develop new drugs. In the 1940s, penicillin could effectively treat most bacterial infections, but today many strains resist multiple antibiotics. This resistance emerges through natural selection—when antibiotics kill susceptible bacteria, resistant ones survive and multiply. Overuse of antibiotics in both medicine and agriculture has accelerated this process dramatically. Scientists now warn that without new approaches to fighting bacterial infections, we may enter a "post-antibiotic era" where common infections become life-threatening again, much as they were before the discovery of penicillin.

Question:

Which choice best states the main idea of the text?

Answer: C

Explanation: Apply "Topic + So What?" — Topic: antibiotic resistance. So What: It's a growing threat that could create major health problems. Option C captures both the problem (rapid resistance evolution) and the consequence (serious public health risks/post-antibiotic era). Options A, B, and D are all supporting details that explain HOW or WHY this problem exists, but they don't state the overarching concern. The passage's opening and closing sentences emphasize the threat, making C the comprehensive main idea.

The monarch butterfly's annual migration from Canada to Mexico is one of nature's most remarkable journeys. Each fall, millions of monarchs travel up to 3,000 miles to reach oyamel fir forests in central Mexico, where they cluster in dense colonies on tree branches. No individual butterfly completes the full round-trip migration; instead, the journey spans multiple generations. Monarchs that migrate south in the fall live for 6-8 months—far longer than the typical 2-week lifespan of summer generations. Scientists believe these migratory monarchs navigate using a combination of the sun's position and an internal magnetic compass, though the exact mechanisms remain under investigation.

Question:

According to the text, how long do monarch butterflies that migrate south in the fall typically live?

Answer: C

Explanation: This is a straightforward details question. The passage explicitly states: "Monarchs that migrate south in the fall live for 6-8 months." Option A (2 weeks) refers to summer generations, not fall migrants. Option B (3,000 miles) is the migration distance, not lifespan. Option D (multiple generations) describes how long the round-trip takes, not an individual butterfly's lifespan. Always read carefully and match the specific detail being asked.

📚 Daily Practice Routine

• Read 1-2 short passages daily (200-300 words)
• Practice summarizing main idea in one sentence
• Complete 5-7 Central Ideas questions per day
• Review why wrong answers were incorrect
• Time yourself: 60-90 seconds per question

🎯 Skill Building

• Read diverse materials (science, history, literature)
• Practice the "Topic + So What?" formula constantly
• Learn to spot topic sentences quickly
• Develop strong paraphrasing skills
• Build vocabulary for discussing main ideas

⏱️ Test Day Strategies

• Main idea questions take longer—budget 75-90 seconds
• Read the entire passage before answering
• Annotate key points as you read
• Make your prediction before looking at choices
• Use process of elimination confidently

📖 Related Skills

• Command of Evidence: Textual
• Command of Evidence: Quantitative
• Inferences
• Purpose and Function