ACT® · Reading — Key Ideas and Details: Central Ideas, Themes, and Summaries
Too Narrow, Too Broad, Just Right
The right main idea answer is sized to match the passage exactly: not one detail blown up, not a vague claim stretched over it, but the one statement the whole passage was built to support.
Every main idea question hands you choices that are all true, which is exactly the trap. A choice can be lifted straight from the text and still be wrong, because truth isn't the test. Size is. Picture the passage as a circle. A too-narrow choice is a small circle sitting inside it, covering one sentence or one example but leaving most of the passage unexplained. A too-broad choice is a huge circle that swallows the passage and a dozen other passages too, true of the topic in general but not stating what this particular text actually argues. The correct choice is the circle that matches the passage's own outline, point for point.
The reason more coverage doesn't mean safer is that breadth and accuracy aren't the same thing. A broad claim about medieval towns, or about Scottish engineering, is safely true, but safe and true isn't the job, the job is matching the shape. The passage has a specific claim it spends its sentences proving, and the right answer names that claim, no more, no less. This gets trickier when a passage spends half its length on one long example, like the Danish shipping register. The example feels like the main idea because it dominates the word count, but its job is to support the real claim, which sits in the sentences around it explaining why the example matters.
This same sizing move reappears in function questions about a single paragraph: a paragraph can spend all its words on one detail while its function is the larger point that detail is serving, so match purpose, not word count. Get comfortable asking, after every choice, does this circle match the passage, or just sit inside it or around it.
Key terms
- Too narrow
- A choice that restates one detail or example instead of the claim the whole passage supports.
- Too broad
- A choice that is true of the general topic but not specific to what this passage actually argues.
- Nested circles
- A way of picturing main idea choices by size: too small, too large, or matching the passage exactly.
- Dominant example
- A long example that takes up much of a passage's length without itself being the main idea.
Watch it explained
- How it worksHow do nested circles show a choice that is too small, too large, or exactly the right size?
- Worked exampleShow me sizing three candidate main ideas against a text on why medieval bridges carried shops.
- Common mistakeWhy doesn't covering more of a text make a broader choice the safer one?
- Going furtherWhat happens to circle sizing when a text spends half its length on one example?
- Ties togetherHow does the too-narrow trap reappear in a question about a single paragraph's function?
Check yourself
End of topic.