Theory, Law, and Hypothesis in Science

Recognize how three common words carry precise, different meanings in scientific writing.

In everyday speech, 'theory' often means a hunch: 'My theory is that the bus is late because of rain. ' In science, a theory is the opposite of a hunch. It is a well-tested explanation that accounts for a large body of evidence, such as the theory of plate tectonics. A hypothesis is a specific, testable prediction that may or may not hold up. A scientific law describes a pattern, often mathematically, without necessarily explaining why it happens; the law of conservation of mass states that mass is not created or destroyed in a chemical reaction.

Worked example: 'Evolution is only a theory. ' A reader who knows scientific usage sees the confusion. Calling something a theory in science is high praise, not a sign of doubt. Recognize these words instantly in their disciplinary sense, or you will misread the strength of a claim.

• 1A scientific theory is a well-tested explanation, not a guess.
• 2A hypothesis is a testable prediction.
• 3A law describes a pattern; a theory explains it.