How to find the main idea

Finding the main idea in a reading passage is one of the most important reading comprehension skills.  Because of that, questions about the main idea repeat on the SAT and ACT and on almost every reading test from second grade through college.  So how do you find the main idea?

In a one-paragraph passage, the main idea is almost always stated in the first sentence, called the topic sentence.  A student can figure this out because the rest of the paragraph contains details about that first sentence.

Some students think a main idea and a topic are the same thing.  Wrong.  A topic can be stated as a single word or a phrase, but a main idea can be stated only as a complete sentence.  For example, a topic might be “dogs,” but a main idea might be “Boxers are the best dogs,” or “Dogs need to be bathed every week,” or “Dogs come in all sizes.”

If a writer begins a paragraph with a hook, the main idea might not be in the first sentence.  It might be in the second sentence.  Or it might be in the last sentence where the writer repeats the main idea to be sure the student has found it.

Another place to look for the main idea is in the title or headline.  Sometimes the title or headline contains hooks to lure a student to continue reading.  But many times they identify the topic, and sometimes they state the main idea.

As students read longer passages, they should still expect to find the main idea in the beginning paragraph.  However, it might be found routinely in the last sentence of that first paragraph.  The earlier part of the paragraph introduces the topic of the passage, but the main idea is stated in the last sentence of that paragraph.  Many writers repeat the main idea—not in exactly the same words—in the conclusion.

Look at the first sentences in the body paragraphs.  Those first sentences should be backing up an idea.  Many times that idea is stated in those sentences.

In longer passages, a strong clue to the topic is a word or phrase or its synonyms which are repeated more than any other idea in the passage.  For example, “Water pollution,” “river trash,” “ocean dead spots,” and “toxic runoff” all are types of water pollution.  These words tell the topic, but they don’t tell the main idea.  But with the idea of water pollution, students can go back to the first paragraph and the last paragraph to narrow in on the topic sentence.

Another way for young children to identify the main idea is to ask questions:

  • Who is the passage about? No one in particular?  Then keep looking.  But if it is a particular person or group whose name is repeated, the main idea probably has something to do with them.
  • What is the passage about? Every passage is about something.  Put into your own words what the passage is about.  Now go back and see if you can find evidence backing up your conclusion.
  • Are there numbers in the passage? If so, numbers about what?  Numbers usually back up or prove something.
  • Do illustrations give a clue?  Sometimes art can help a young student figure out the topic.  Knowing the topic, a student can look in the usual places for the main idea.

Sometimes a writer talks around a topic, implying a main idea without stating it, at least at first.  The writer does state the main idea eventually, but it might not be where you expect.

Why is identifying the main idea so important?  As a student grows older, he or she will need to learn more and more from what he or she reads, and less and less from what a teacher says.  That student will need to be able to identify quickly what the main idea is in order to make sense of an article or book or research paper.  When a student does research, he or she will need to be able to analyze information to see if it is relevant.  The most important skill to do that is to identify the main idea.

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