What Is a Scientific or Natural Law?

A law in science is a generalized rule to explain a body of observations in the form of a verbal or mathematical statement. Scientific laws (also known as natural laws) imply a cause and effect between the observed elements and must always apply under the same conditions. In order to be a scientific law, a statement must describe some aspect of the universe and be based on repeated experimental evidence. Scientific laws may be stated in words, but many are expressed as mathematical equations.

Laws are widely accepted as true, but new data can lead to changes in a law or to exceptions to the rule. Sometimes laws are found to be true under certain conditions, but not others. For example, Newton's Law of Gravity holds true for most situations, but it breaks down at the sub-atomic level.

Scientific laws do not try to explain 'why' the observed event happens, but only that the event actually occurs the same way over and over. The explanation of how a phenomenon works is a scientific theory. A scientific law and a scientific theory are not the same thing—a theory does not turn into a law or vice versa. Both laws and theories are based on empirical data and are accepted by many or most scientists within the appropriate discipline.

For example, Newton's Law of Gravity (17th century) is a mathematical relation that describes how two bodies interact with each other. The law does not explain how gravity works or even what gravity is. The Law of Gravity can be used to make predictions about events and perform calculations. Einstein's Theory of Relativity (20th century) finally started to explain what gravity is and how it works.