Hypothesis

A hypothesis is a scientist's best guess about why something happens. It is not just any guess though. A hypothesis is based on what you already know and can be tested with an experiment. If the experiment supports the hypothesis, it might be correct. If not, the scientist makes a new hypothesis and tries again.

Making a Good Hypothesis

A good hypothesis is specific and testable. Instead of saying plants need light, a good hypothesis would be plants that get eight hours of light will grow taller than plants that get four hours. This is specific enough to test. A hypothesis should also be falsifiable, meaning it must be possible to prove it wrong.

Testing a Hypothesis

To test a hypothesis, scientists design experiments. They change one thing, called a variable, and keep everything else the same. This way, they can see if that one change makes a difference. If the results match the hypothesis, it is supported. If not, the scientist learns something new and can form a better hypothesis.

Fun Facts

• The word hypothesis comes from the Greek words for under and placing, meaning a foundation for reasoning.
• Some of the best scientific discoveries came from hypotheses that turned out to be wrong.
• Albert Einstein's hypothesis about relativity was not fully proven until years after he proposed it.

Did You Know?

A hypothesis is different from a theory. A hypothesis is a single testable guess. A theory is a well-tested explanation that has been supported by many experiments over many years. The theory of gravity, for example, started as a hypothesis but has been tested and supported thousands of times!