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Teacher question:

Can you explain the difference between central idea, main idea, and theme? There appears to be a lot of confusions with these terms. 

Shanahan’s response:

You’re correct. There is much confusion and disparity in use of the terms central idea, main idea, and theme. And please add topic and topic sentence to that list, too.

Part of the problem here is that these are old colloquial terms. They didn’t arise from the sciences (e.g., psychology, linguistics), so, perhaps, we shouldn’t expect too precise a meaning for each.

Back in the early 1980s, Jim Baumann conducted a series of studies on the “main idea” concept and the steps needed to teach students to identify main ideas. He found that professional books and teacher’s manuals were all over the map when it came to main idea. The term was used in lots of disparate ways and the teaching steps evident in various programs were unlikely to lead kids to be able to identify main ideas. His work is still among the best on how to teach kids to do this.

The term “main idea” has been used in a variety of ways for over 200 years… Sometimes main idea has been limited to summary statements about briefer portions of a text like paragraphs (e.g., main idea is often used as a synonym for topic sentence — and topic sentence instruction is often used as the route to teaching main idea). But there are scads of examples of main idea with regard to entire texts, too.

Sometimes the term “main idea” has been reserved for summarizing the major thought or point behind expository or informational texts only. But even a quick perusal of the educational literature reveals a great deal of inconsistency in that approach. The earliest mentions of “main idea” that I have found refer to the major lessons to be learned from religious stories in the 1850s.

The only consistency evident in main idea is its focus on the big idea that a text is expressing. 

The term “central idea” has been used just as long, but a bit less often, and its use seems even more general. I suspect it has become popular as a synonym for main idea since Baumann’s eye-opening work in the 1980s.  Users, perhaps eager to avoid these confusions, employ central idea in the hopes that we’ll understand it better than we would have if they’d used main idea. If so, they have failed. Whatever main idea means in reading, central idea is its synonym — no more and no less.

Theme, on the other hand, is a term that arises from literature, and it is usually incorrect to apply it to most informational texts. A theme is the point or central idea of a literary work … it may be stated in terms of a point of view (e.g., unchecked ambition is dangerous to all) or as a single word (e.g., love, death). Usually literary works express multiple themes — sometimes even conflicting themes — and readers have to learn coordinate, synthesize, or choose from among these thematic expressions to arrive at a rich interpretation of a literary work.

It might be okay to sometimes use terms like main idea or central idea to refer to this overall thematic interpretation, but it wouldn’t work to apply them to the conflicting themes underlying this overall theme of a work.

If these terms are confusing, instruction often makes matters worse. For example, kids are often taught that the first sentence of a paragraph states its main idea. This is true, of course; except in those instances where it is the last sentence, or one of the middle sentences, or it isn’t stated explicitly at all.

Or, students may be taught that a text has a single main idea. Again, a notion that is correct, except whenever it isn’t. Think of reading an encyclopedia entry on Japan. Perhaps one could say “the main idea is Japan” (the topic) which is not particularly satisfying (most reading teachers would rightly reject that one — main ideas and topics shouldn’t be used interchangeably), or that “it is an article that tells a lot of facts about Japan, a country in Asia” (which is a reasonable description of the purpose of the entry, but which seems a bit thin on substance).

My hunch is that the problem here is that we are trying to state a single main idea when this kind of text is a slew of main ideas. “This entry tells facts about Japan, a country in Asia. It describes Japan’s history, politics, military, economy, science and technology, infrastructure, demographics, and culture.” Maybe not entirely satisfying yet because it is little more than a string of topics, but I think you’ll agree that it is a whole lot closer than those previous attempts.

There has been interesting research done — both with human readers and computer readers — to try to come up with an operational definition of main or central idea that would be a bit less squishy. That work has focused on expository/informational text alone and usually homes in on main idea by how often they are referred to throughout the text. The more the various sentences connect to a particular idea, the more likely it is integral to the main idea that the author is trying to put across.

(I wonder if the term “central idea” has been latched onto recently as a way of trying to capture this perception that all of the other ideas connect up to some central idea. For instance, my wife, Cyndie, says she prefers to think of the main idea is being at the top of a hierarchy, with all of the other ideas connected below it.)

Look, for instance, at these paragraphs from a Newsela article (opens in a new window):

What’s the main or central idea of the first paragraph?

It certainly isn’t the first sentence.

In fact, I don’t think it would be possible to select any sentence in paragraph 1 as a main idea. Perhaps one could craft a main idea statement by combining sentences 1 and 2, though that certainly skips a lot of important information.

From a paragraph like that, it’s easy to see why someone might conclude that topics and main ideas are the same thing. But I don’t buy that the paragraph’s main idea is “Alaska’s Denali National Park and Preserve.” Perhaps this is like the encyclopedia entry: the main idea is how incredible Denali National Park is in terms of its size and what’s found there.

In Paragraph 2, it might even help to ignore the first sentence. A good main idea for this one could be:  In Denali, the park rangers depend upon sled dogs for transportation.

The main idea of Paragraph 3 seems to be placed right in the middle: Sled dogs are more reliable transportation in Denali than machines because they handle the cold weather better than machines do.

And, finally, Paragraph 4, the dogs help the rangers to get to hard-to-reach parts of the park.

Though it is possible to come up with “main ideas” for each of these paragraphs, one also could say that the complete text has an overall point or main idea as well.

Here is where it can help to notice which ideas get repeated and referenced most.

The challenge of Denali (its size, climate, transportation problems, etc.) comes up in all four paragraphs. The dogs’ ability to conquer these problems is noted in paragraphs 2, 3, and 4, as does the notion that these dogs’ abilities are relied upon by Denali’s rangers.

A main idea for this — because of the number of repetitions of each of these ideas and the linking of them to each other — might result in something like: “The Denali National Park is very large, cold, and snowy so transportation is difficult. Because of that, the Denali rangers need to rely upon sled dogs for transportation.”  

The big take away (or, my main idea)?

Despite all the messiness of this terminology…

Everyone agrees that good readers must make these kinds of summary statements about the major, chief, main, key, foremost, or central ideas of informational and argumentative texts.

And, good readers also can identify multiple themes from literary texts. See my earlier blog entry on what it means to teach theme, Teaching Kids to Interpret Theme: The Limits of Practice

Good readers have to be able to identify these major ideas — the ones that state the point of the text or that are the most repeated or referenced ideas of the text — with paragraphs, sections of texts, and entire texts.

These main idea statements can be dinged for being too general (such as just stating the topics Denali or Japan) and they can be too specific (citing too many of the specific details instead of some generalization that captures the whole set of ideas). In other words, they need to learn to identify the Goldilocks main idea, the one that is “just right.”

Textbooks and state educational standards use these terms somewhat inconsistently and interchangeably. That just reveals the imperfections of language when addressing such abstract ideas that vary so much by context (think of my various examples above).

Don’t get misled by these linguistic inconsistencies. There are no fine distinctions that are being hidden from you. You just have to nurture the ability to capture these big ideas from a wide variety of texts across a wide variety of genres.


About the Author

Literacy expert Timothy Shanahan shares best practices for teaching reading and writing. Dr. Shanahan is an internationally recognized professor of urban education and reading researcher who has extensive experience with children in inner-city schools and children with special needs. All posts are reprinted with permission from Shanahan on Literacy (opens in a new window).

Publication Date
March 6, 2018