Central Ideas and Details
Every Reading passage is built around one main point — and the test loves to ask you what it is. If you can nail the central idea, you'll answer these questions fast and avoid the traps.
How to vet a main-idea answer choice.
Signal words flag the shift from the rejected old view to the author's actual point.
Check your understanding with a question from this topic:
Atmospheric scientists have identified a previously unknown feedback mechanism in Arctic climate systems. As permafrost thaws, it releases not only carbon dioxide but also ancient methane deposits trapped beneath frozen soil layers. These methane emissions may accelerate warming at rates 20% faster than current climate models predict.
The passage suggests that current climate models may be
Worked examples
A team of geologists studying a remote mountain range found that certain rock layers contained fossils of marine organisms. Because these layers now sit thousands of meters above sea level, the researchers concluded that the region was once covered by an ancient ocean before tectonic forces lifted it.
Which choice best states the main idea of the passage?
Astronomers once assumed that planets could only form around stars similar in size to our Sun. Recent observations, however, have revealed fully formed planets orbiting tiny, dim stars called red dwarfs — bodies far smaller and cooler than previously thought capable of supporting planet formation.
The passage is primarily concerned with
Historians long believed that a particular medieval trade route declined because of war. New analysis of merchant records, though, suggests the route actually thrived during wartime; its decline came decades later, when a shift in river courses made the path impassable for cargo boats.
According to the passage, the trade route ultimately declined because
Common pitfalls
A choice can state a real fact from the passage and still be wrong for a main idea question if it only covers part of the text. The central idea must account for the whole passage, not one sentence.
When a passage says "researchers once assumed" or "traditional models suggest," that old idea is bait. The author is usually overturning it — so an answer restating the old view is a classic trap.
Choices that make grand claims ('all mountains,' 'every species') usually overreach what the passage actually says. The answer must stay inside the text — don't add what you happen to know is true.
For detail questions, if you can't point to a specific line that supports the choice, it's wrong — even if it seems plausible. Always locate the supporting sentence.
Key takeaways
The central idea is the ONE point the whole passage supports — it must cover everything, not just one sentence.
Signal words like 'however,' 'but,' 'instead,' and 'yet' usually point straight at the main claim.
When a passage describes an old assumption and then corrects it, the new claim is the central idea — and the old view is a trap answer.
Detail questions want a paraphrase of something the text literally states; if you can't find the line, eliminate it.
Predict the answer in your own words before reading the choices to avoid being lured by plausible distractors.
Watch & learn
Curated Khan Academy walkthroughs on Central Ideas and Details. They're complementary to this lesson — watch one if a written explanation isn't clicking, or after to reinforce.
Try it yourself
5 practice questions on Central Ideas and Details, drawn from the question bank. The tutor is one click away if you get stuck.