What is a main idea?

Topic

Imagine that you are reading the newspaper. Your friend asks: “What are you reading about?” You might answer:

• “I’m reading about the Bulls game.”
• Or “I’m reading about construction on the CTA.”
• Or “I’m reading about the economic recession.”

The Bulls game, construction on the CTA, and the economic recession are examples of topics! A topic is simply what the text is about. A topic is generally one to five words long. It does not express an opinion, and is not a full sentence with a verb and an adjective. If you are having trouble determining the topic of a reading, look for words and/or concepts that are repeated​ several times.

Controlling idea

Knowing the topic is just the beginning!​ To find the main idea, you must also know what the author has to say about the topic. Let's imagine you have told your friend you are reading about the economic recession. Your friend says, “Oh yeah? What about it?” You might answer…

• “The economic recession is likely to end soon.”
• Or “The economic recession is worse in rural places than in cities.”
• Or "The economic recession was caused by banks making irresponsible loans."

The bolded part of each of these sentences is the second part of the formula—the controlling idea.

Please note that this idea can be a fact or an opinion.

Putting it together

All three sentences above are examples of main ideas. They all have the same topic—the economic recession. But each sentence expresses a different controlling idea about the same topic.

A main idea needs those two parts—the topic and the idea about it—but it doesn't matter what order they go in. So you could also say “Irresponsible loans made by banks caused the economic recession.”

PowerPoint: What's the Main Idea?