Main idea and key details

What is the main idea?

When you finish reading, a good question to ask is: “What was that mostly about?” Your answer is the main idea.

The main idea is the most important point the author wants you to know. The key details are the facts that tell more about the main idea.

Think of a table. The tabletop is the main idea. The legs are the key details. The legs hold up the tabletop, just like details hold up, or support, the main idea. That is why key details are also called supporting details.

Topic and main idea are different

The topic is the subject, usually one or two words: bees.

The main idea is a whole sentence that tells the most important point about the topic: Bees are busy insects that help plants grow.

Why it matters

Finding the main idea helps you:

• Understand what you read.
• Remember the important parts.
• Tell others about what you read.
• Write your own clear paragraphs.

Where to find the main idea

In the title or heading

The title or heading often tells the topic, and sometimes the main idea. A heading like How Frogs Grow tells you the section is about the life cycle of frogs.

In the first or last sentence

Authors often put the main idea in the first sentence of a paragraph. Sometimes it is in the last sentence, like a wrap-up.

By thinking about all the details

Sometimes the main idea is not written in one sentence. Then you must look at all the details and ask, “What do these all have in common?”

How to find the main idea and key details

1. Read the whole paragraph or page.
2. Name the topic. Who or what is it about?
3. Ask: what is the author telling me about the topic? That is the main idea.
4. Find details that tell more. Underline them or count them on your fingers.
5. Check: Do the details all support your main idea? If not, change your main idea.

Let’s try an example

Penguins are birds that are built for cold water. They have thick feathers that keep them warm. Under their skin is a layer of fat called blubber. Their wings are shaped like flippers, which help them swim fast.

• Topic: penguins
• Main idea: Penguins are built for cold water.
• Key details:
  1. They have thick feathers that keep them warm.
  2. They have a layer of blubber.
  3. Their flipper wings help them swim fast.

Every detail supports the idea that penguins are made for cold water.

Another example: the hidden main idea

Maya packed sunscreen, a towel and her swimsuit. She grabbed her shovel and pail. She put on her sunhat and ran to the car.

No sentence says the main idea. But all the details point to the same thing: Maya is getting ready to go to the beach.

Not every detail is a key detail

Some details are interesting but not important. Read this:

Owls hunt at night. They have big eyes that see well in the dark. They can fly without making a sound. My aunt has a mug with an owl on it.

The mug is a fun fact, but it does not tell us about how owls hunt at night. It is not a key detail.

Using main idea to write a summary

A summary is a short retelling of a text. To write one:

1. Write the main idea in one sentence.
2. Add two or three key details.
3. Leave out small, extra details.

Summary: Penguins are built for cold water. They have thick feathers and blubber to stay warm, and flipper wings to swim fast.

Common mistakes

• Giving only the topic. “Penguins” is a topic, not a main idea. Say a whole sentence.
• Choosing a detail as the main idea. “Penguins have blubber” is a detail. The main idea is bigger.
• Making the main idea too big. “Birds” is too big when the paragraph is only about penguins.
• Including unimportant details in your summary.

Try it yourself

Trees help people and animals in many ways. They give us shade on hot days. Their leaves make the oxygen we breathe. Birds and squirrels build their homes in trees.

1. What is the topic?
2. What is the main idea?
3. List three key details.
4. Write a one-sentence summary.

Answers: 1. Trees. 2. Trees help people and animals in many ways. 3. Shade; oxygen; homes for birds and squirrels. 4. Trees help people and animals by giving shade, oxygen and homes.

Tip for families

After reading a short informational book, ask, “If you had to tell a friend what this book was about in one sentence, what would you say?” Then ask, “What were two things the book told you about that?” Practising out loud makes the skill easier when your child writes.

Quick recap

• The topic is what a text is about in a word or two.
• The main idea is the most important point, said in a sentence.
• Key details tell more about and support the main idea.
• Look in the title, the first sentence and the last sentence.
• Use the main idea and key details to write a summary.