01 // What a hypothesis is
A hypothesis is a specific, testable prediction about what will happen in an experiment — not just any guess. It names the variable you plan to change (the independent variable), the variable you plan to measure (the dependent variable), and it explains why you expect that result based on what you already know.
A good hypothesis is falsifiable: there has to be a possible result that would prove it wrong. "Plants are affected by light" is too vague to test. "If a bean plant gets 12 hours of light a day instead of 6, then it will grow taller after two weeks, because more light gives the plant more energy for photosynthesis" is specific enough to test and specific enough to fail.
02 // The if-then-because template
Fill in three blanks: what you change, what you expect to happen, and the reason you expect it.
| If (independent variable) | a bean plant gets 12 hours of light per day instead of 6 |
| Then (dependent variable + direction) | its height after two weeks will be greater |
| Because (the reasoning) | more light gives the plant more energy for photosynthesis |
Formula If [I change this], then [this will happen], because [this is why].
03 // What makes a hypothesis weak
- No predicted direction. "Light will affect growth" does not say taller, shorter, faster, or slower — it can never be wrong, so it is not testable.
- Two variables changed at once. "More light and more water will make it grow taller" — if it grows taller, you cannot tell which one caused it.
- No reasoning. The "because" clause forces you to connect the prediction to real science, and it is usually the part a rubric checks first.
- A hypothesis is not the same as a research question. The question is "does more light make plants grow taller?" The hypothesis is the specific if-then-because answer you predict.
04 // Questions people ask
What is the difference between a hypothesis and a theory?
A hypothesis is a single testable prediction for one experiment. A theory is a broad, well-tested explanation supported by many experiments and observations over time, like cell theory or the theory of plate tectonics.
Does a hypothesis have to turn out correct?
No. An experiment that disproves a hypothesis is still a successful experiment, as long as it was a fair test. Many important discoveries started with a hypothesis that turned out to be wrong.
What is a null hypothesis?
The null hypothesis predicts no effect or no difference — for example, "the amount of light will not change plant height." Scientists often test against the null hypothesis to see if their data shows a real effect or just random variation.