Main-Idea Detection
The main idea is the single sentence-length point the entire passage is trying to make. Everything else — examples, statistics, anecdotes, quotes — exists to support it. Main-idea questions are written in several ways: "The main idea of this passage is…", "The author is primarily concerned with…", "The best title for this passage would be…", "This passage is mostly about…". Treat them as the same question.
Where the main idea hides. In most ASVAB passages the main idea is stated, not buried. The two highest-percentage places to look: 1. The first sentence. The author introduces the claim, then spends the rest of the passage backing it up. 2. The last sentence. The author walks through evidence and then states the conclusion.
A smaller share of passages put the main idea in the middle and surround it with setup and follow-up. Even then it is rarely implicit.
Main idea vs. topic vs. detail. - Topic: What the passage is about, in two or three words. ("solar storms," "the GI Bill") - Main idea: The full point the author makes about that topic, in a complete sentence. ("Solar storms can disrupt power grids and satellite communications, so utilities have begun investing in forecasting.") - Detail: A specific fact, number, name, or example used in support. ("In 1989, a geomagnetic storm caused a 9-hour blackout in Quebec.")
The wrong answers on main-idea items almost always swap one of these for another. A choice that restates a single supporting detail is too narrow. A choice that broadens the topic to all of space weather is too wide.
Filter the four choices through three tests: 1. Scope: Does it cover the whole passage, not just one paragraph or one example? 2. Accuracy: Does the passage actually say this, in essence? 3. Direction: Does it match the author's stance? An author who criticizes a policy does not have a main idea that endorses it.
If two choices both pass, the more specific one usually wins. A correct main idea reflects the particular claim the author makes, not a vague platitude about the topic.
Title questions are main-idea questions in disguise. A correct title is short, specific, and covers the entire passage — never just one detail.