SAT Reading & Writing: Main Purpose and Central Idea
44+ practice questions in Praczo
The concept, explained
- 1
Main purpose is what the author is trying to accomplish: to argue, explain, describe, compare, or analyze. Central idea is the most important claim the passage makes about its topic.
- 2
Topic ≠ central idea. Topic = "coral reefs." Central idea = "coral reef degradation threatens both ecosystems and human communities." The central idea makes a specific claim.
- 3
Ask yourself: "Why did the author write this? What would be lost without it?" The answer is the main purpose.
- 4
Wrong answers are typically too narrow (covering only one paragraph's detail) or too broad (claiming more than the passage actually argues).
- 5
The first and last sentences of the passage — and each paragraph — often signal the central idea. But read all the way through before deciding.
- ✗ Choosing an answer that is true and appears in the passage but only describes one section of it — the main purpose must span the whole passage.
- ✗ Confusing topic with central idea and selecting an answer that merely names the subject without capturing the author's argument.
SAT-style practice
A passage describes how coral reefs provide habitat for thousands of marine species, protect coastlines from wave erosion, and support fishing industries — before concluding that reef degradation threatens both ecosystems and human communities. Which best describes the main purpose?
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