Finding Causes and Effects

By the end of this lesson, you will be able to spot a cause-and-effect relationship and use it to explain something that happens in the world around you.

A cause-and-effect relationship means one event or condition, called the cause, makes another event, called the effect, happen. Scientists look for these links in every field, from weather to biology to chemistry, which is why cause and effect is called a recurring theme. Once you can trace a cause to its effect, you can explain a phenomenon or start solving a problem.

Think about a kiddie pool left sitting on a St. Augustine lawn in a Texas backyard for two weeks in July. When you finally drag the pool away, the grass underneath is pale yellow instead of green. The cause is the pool blocking sunlight; the effect is grass that cannot make enough food and loses its color. Notice that the grass just outside the pool's edge stayed green, which is strong evidence that the pool, not the heat, caused the change.

That comparison matters, because two things happening together does not always mean one caused the other. Ice cream sales and mosquito bites both rise in June, but ice cream does not create mosquitoes. Summer heat affects both. To test a real cause, scientists change only one variable, which is a factor that can change in an investigation, and keep everything else the same.

You can investigate cause and effect yourself. Ask what changed, look for a pattern, and then design a fair test where only your suspected cause is different between two setups. If the effect disappears when you remove the cause, your explanation is probably correct.

Try it: If your bedroom window fogs up on a cold morning but the wall next to it does not, what is the most likely cause of the fog on that one surface?