The main idea is the essential point of a paragraph or text: if you remove it, the text loses its meaning. Supporting details are the sentences that explain, prove, describe or illustrate the main idea: if you remove them, the text becomes less convincing or less clear, but its basic message survives. Learning to separate the two is the key to taking notes, annotating and summarizing.
What supporting details do
A supporting detail always depends on a bigger idea. It usually does one of these jobs:
- Gives an example: a specific case (for example, for instance, such as).
- Explains or clarifies: says the same thing in another way (in other words, that is).
- Provides facts: numbers, dates, names or places.
- Gives reasons: causes or justifications (because, since).
- Shows effects: what follows from the main idea (as a result, so).
- Compares or contrasts: links the idea to something similar or opposite.
Three tests to tell them apart
- The removal test. Cover the sentence and read the paragraph without it. If the paragraph still makes sense, the sentence is a supporting detail. If the paragraph no longer has a clear point, you have covered the main idea.
- The dependence test. Ask whether the sentence needs another one to make sense. For example, the Iberian lynx cannot stand alone: it depends on the statement it illustrates.
- The umbrella test. The main idea is usually more general; supporting details are more specific. If one sentence works like an umbrella that covers all the others, it is probably the main idea.
A worked example
Read this paragraph:
Getting enough sleep is essential for learning. While we sleep, the brain sorts and stores the information we took in during the day. That is why students who stay up all night before an exam often remember less of what they reviewed. Tiredness also makes it harder to concentrate the next day.
- Main idea: Getting enough sleep is essential for learning.
- Supporting detail (explanation): during sleep the brain stores what was learned.
- Supporting detail (effect): students who skip sleep before an exam remember less.
- Supporting detail (additional reason): tiredness makes concentration harder.
If you remove the first sentence, the paragraph loses its focus; if you remove any of the others, the message stays the same.
Major and minor details
Some teachers divide supporting details into two levels. Major details directly support the main idea; minor details support a major detail, often with an example or a number. In a summary you keep the main idea and, if there is room, the major details, and you leave out the minor ones.
Paragraph main ideas and the central idea
In a longer text, each paragraph has its own main idea, and the whole text has one central idea. In relation to that central idea, the main ideas of the paragraphs act almost like supporting details: each one develops a different side of it. A practical approach is to write down the main idea of every paragraph and then build the central idea from that list.
When you have your answer, you can check it with the tool below, which suggests the main idea of any text you paste. Use it as a second opinion: if its answer differs from yours, reread the passage and decide, with your own reasons, which one fits better.
How to annotate a passage
- Read once without a pen. Get the big picture first; if you highlight on the first read, you will end up marking almost everything.
- Reread paragraph by paragraph. In each one, find the sentence or the words that carry the main idea.
- Highlight little. Mark key words, not whole sentences. What you mark should make sense when read on its own.
- Use two kinds of marks. For example, one colour or a solid underline for main ideas and another colour or a dotted line for the most useful details.
- Write margin notes. A word next to each paragraph (causes, example, conclusion) shows you how the text is built.
Common mistakes
- Confusing the most striking sentence with the most important one: a surprising fact or a vivid example is usually a detail.
- Assuming the main idea is always the first sentence of the paragraph.
- Highlighting so much that main ideas and details look the same.