Identifying the Main Idea

The main idea is the sentence that makes the central point about the topic or subject of a paragraph.

The strategies explained in this section are:

  1. Making your own main idea.

Ask three key questions:

  • What is the topic?
  • What is listed about the topic?
  • What do the major details have in common?

Before clocks were made, people kept track of time by other means. In ancient Egypt, people used a water clock. Water dripped slowly from one clay pot into another. People measured time according to how long it took one pot to empty and the other one to fill. Candle clocks were common during the Middle Ages. As such, when a candle burned, marks on its side showed about how much time had passed. A final ancient way to measure time was the sundial, which used the movement of the sun across the sky. The shadows moving across the face of the sundial showed the current time.What is the main idea?

1 One common example of instinct is the spider's spinning of its intricate web. 2 No one teaches a spider how to spin: its inborn instinct allows it to accomplish the task. 3 Another example of instinctive behavior is the salmon's struggle to swim upstream to lay eggs. 4 It would be much easier for the salmon to follow the current downstream, but instinct overrides all other considerations. 5 Instinct is clearly a strong influence on animal behavior.What is the main idea?

1 In response to customers' bitter complaints about long lines, banks are trying new ways to shorten the wait or at least to make it more pleasant. 2 One bank provides coffee and cookies so customers can munch while they wait. 3 Other banks show action movies on a large video screen. 4 One daring bank in California will pay a customer five dollars if he or she must wait more than five minutes for service. 5 Still other banks offer the most obvious solution of all...they simply hire more bank tellers.

Caffeine is a natural ingredient in coffee, cocoa, tea, and chocolate, and is added to some prescription and non-prescription drugs. 2. Despite being "natural," caffeine is also a powerful drug which greatly affects the body. 3. In healthy, rested people, a dose of 100 milligrams (about one cup of coffee) increases alertness, banishes drowsiness, quickens reaction time, it enhances intellectual and muscular effort, and increases heart and respiratory rates. 4. Drinking one to two cups of coffee an hour before exercise encourages the body to preserve glycogen and burn fat -----something that results in greater endurance. 5. In addition, caffeine masks fatigue. 6. In doses above 300 milligrams, caffeine can produce sleeplessness, nervousness, irritability, headaches, heart palpitations, and muscle twitches. 7. Caffeine is also habit-forming, and those who try to suddenly stop after heavy use may experience such withdrawal symptoms as headaches, lethargy, irritability, and difficulty in concentrating.The main idea of this passage is that caffeine

Though fun to watch, chimpanzees should not be kept as pets. 2. They are dangerously stronger that any NFL lineman. 3. Adult chimps weigh only 100 to 160 pounds, but have been measured pulling six to nine times their own weight-----with one hand. 4. Thus, to match the strength of an average chimp, a human being would have to be able to register a two-handed pull of about a ton it takes a very strong man to pull a quarter of that. 5. Combined with this strength is the fact that a chimp is capable of losing its temper -----for reasons known only to the chimp. 6. Chimps signal their feelings with subtle cues of behavior that aren't apparent to most humans. 7. It is quite possible for a chimp to be on the verge of violence while its owner sits unaware or even unknowingly continuous to provoke. 8. Furthermore, it's not wise to keep a cute young chimp and release it into the wild when it becomes dangerous. 9. Wild-raised chimps will routinely gang up on and kill those raised in captivity. The main idea of this passage is that

Human beings have always polluted their environment, but in the past it was easier for them to move on and live somewhere else. 2.They knew that given time, the environment would take care of pollution they left behind and they relied on the "out of sight, out of mind" philosophy. 3. Today, an increasing human population, which uses an increasing amount of energy sources, no longer has the luxury to ignore pollution. 4. The human population is approximately 7 billion. 5. Our overall energy consumption has gone up by a hundredfold from 2,000 per/person/day to 230,000 per/person/day in modern industrial nations like the United States. 6. This high energy consumption allows us to mass produce many useful and economically affordable organic products that pollute the atmosphere and groundwater damage forests and lakes causing global warming, and even deplete the ozone layer. (Borrowed from a biology textbook) The main idea of this passage is that