Establishing the Main Idea

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What Is It?

An important task of reading comprehension is to determine the importance and meanings of individual words, sentences, paragraphs, sections, chapters, and entire texts. Readers decipher the meanings of words within sentences, of sentences within paragraphs, and so on. As readers begin to grasp main ideas, they better understand the purpose of the details—which further strengthens their understanding of those main ideas.

In understanding the concept of a "main idea," it is useful to distinguish between the following terms: topic, main idea, theme, topic sentence, and purpose.

The topic of a text is the subject, or what the text is about. A topic can be expressed as a noun or a noun phrase. Some examples of topics include recycling, mammals, trees of New England, and names.

An idea is what you say about a topic. Ideas, including the main idea, are expressed as sentences. If someone asks you to identify the main idea of a passage and you respond with a single word, you haven't said enough; you've probably just identified the topic. Some examples of main ideas include:

Recycling is expensive in the short term, but yields long-term savings.
All mammals are the same in certain ways.
The trees of New England are the most beautiful in the world.
It's no fun when someone makes fun of your name.

A theme is an idea that is repeated throughout a text or collection of texts. For example, "the importance of family in shaping identity" is a theme that can be found throughout literature.

A topic sentence is the term used to identify the sentence in a paragraph that contains the main idea. Conventionally, the topic sentence is the first sentence in a paragraph, but not always. It can be at the beginning, the middle, or the end. While some paragraphs don't really have an easily identifiable topic sentence, some have more than one. (Which is the topic sentence in this paragraph?) Nevertheless, topic sentences are useful in determining the relationship between main ideas and supporting details.

For example, consider the following:

All mammals are the same in certain ways. They all have lungs, hair or fur, and the ability to nurse their young.

These two sentences obviously bear an important relationship: the first carries the main idea while the second supplies details that support the main idea.

Finally, we often define purpose as "what the author is trying to say"—as if an author is never quite capable of saying what he or she means. The work of reading comprehension is best understood as a joint enterprise between author and reader. Authors can't communicate properly by themselves. They need readers to understand them.

An author's purpose—or even the main idea—is not always obvious and is often open to interpretation. An author is expected to do his or her best to construct text in a way that readers will understand, and except in the case of certain kinds of mystery novels, we trust that an author will not try to trick us.

In expository prose (non-fiction), an author typically tries to make his or her ideas clear and explicit. Still, we filter even the most direct messages through our own experiences, knowledge, beliefs, and understanding of the meanings of particular words.

Reading fiction is more subjective because main ideas are seldom stated explicitly and are often intentionally hidden, as when they are filtered through the persona of an "untrustworthy narrator" like Nabokov's Humbert Humbert in Lolita.