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Fact: An observation that has been repeatedly confirmed. For example, there are 23 pairs of chromosomes in human cells.

Law: A descriptive generalization about how some aspect of the natural world behaves under stated circumstances. For example, one of Newton's laws of motion that states that for every action, there is an equal and opposite reaction.

Hypothesis: A testable statement about the natural world that can be used to build more complex inferences and explanations. It explains why something occurs. For example if the tomato plants in your garden did not produce as many fruits as the year before, one hypothesis might be that the excessive number of rainy days in the current year interfered with the pollination of the tomato flowers.

Theory: In science, a well-substantiated, overarching explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses. For example, the cell theory states that cells are the basic unit of all living organisms and that all new cells arise from the division of pre-existing cells.

If you want to read more about science, see the online version of Teaching About Evolution and the Nature of Science.

(Adapted from Teaching About Evolution and the Nature of Science)