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The Difference Between a Theory and a Law

The Difference Between a Theory and a Law

When discussing scientific principles, there are two frequently confused terms. A scientific THEORY and a scientific LAW. They describe two very different things.

Laws explain HOW something happens.

A LAW describes the nature of a phenomenon and what happens when certain conditions are present. Laws are established after repeated and verified observations. Laws have no exceptions when framed, and they're rarely revised because they are universally observable.

EXAMPLE: Sir Isaac Newton's Universal Law of Gravitation.

The law states that any two objects, regardless of their mass, exert gravitational force toward one another. The formula most physics students learn is: F = G × [(m1m2)/r2]. Using this law, we can chart the moon's course or calculate what's necessary to put a satellite in orbit. (Notice the law allows you to calculate how something will turn out, but offers no insight into why the law works.)

Theories explain WHY something happens.

A THEORY describes the cause of a phenomenon and why something is happening. The word confuses the general public. When an average person has an idea they want to test, they call it a theory. Scientists call that idea a hypothesis, an educated guess about a way to explain a natural phenomenon.

Same word, two different definitions.

For a scientist, once there is enough evidence, a theory takes shape. A theory for a scientist is something that's proven through experiments and observational studies.

EXAMPLE: Charles Darwin and Alfred Russel Wallace's Theory of Evolution by Natural Selection.

This theory describes how living things change over time. Evolution can be documented when an organism is born with a mutation that allows it to better adapt to its environment, help it survive longer and generally have more offspring. If that mutation becomes dominant, then the species is said to have evolved. (Notice the theory explains why something is happening, but does not predict what will happen.)

The reason it's crucial to understand the difference is so that you don't reveal your ignorance when talking about scientific principles.

For example, people will challenge Darwin and Wallace's Theory of Evolution because it's "ONLY A THEORY." They ignore the definition of scientific theory that it doesn't become accepted until extensive testing, experimentation and observation. That "theory" has been strengthened by over 100 years of additional research, making it a cornerstone of biology. No amount of additional information will ever turn it into a law, because it can never predict HOW those changes will manifest.

A theory does not become a law once there is more evidence. They are describing two different things. However, both theories and laws CAN change when new evidence comes to light.

What’s the difference between a scientific law and theory? - Matt Anticole

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Updated 5/8/2022