scientific theory

[ sahy-uhn-tif-ik theer-ee, thee-uh-ree ]
/ ˈsaɪ ənˌtɪf ɪk ˈθɪər i, ˈθi ə ri /
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a coherent group of propositions formulated to explain a group of facts or phenomena in the natural world and repeatedly confirmed through experiment or observation: the scientific theory of evolution.
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Origin of scientific theory

First recorded in 1755–65
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2023


What is a scientific theory?

A scientific theory is a well-tested, broad explanation of a natural phenomenon.

In everyday life, we often use the word theory to mean a hypothesis or educated guess, but a theory in the context of science is not simply a guess—it is an explanation based on extensive and repeated experimentation. And it’s not the job of theories to become facts—they use available facts to make sense of a broad concept.

Scientific theories explain some of the most familiar and complex phenomena. A few of the best-known scientific theories are the theory of gravity, the theory of evolution, and the theory of relativity.

Scientific theory vs. law

If you ever stop to wonder why some fundamental process happens the way it does, it will most likely be a scientific theory that has the answer you seek. For example, if you have big questions about the movement of the planets in our solar system, the theory of heliocentrism has big answers (spoiler alert: they orbit around the sun). That’s because a theory is not just a single answer but a consistent system of many, many answers backed by supporting evidence.

In other words, a scientific theory is an in-depth, wide-sweeping explanation of a natural occurrence that can’t be proven wrong given our current scientific knowledge. So what’s the difference between a scientific theory, a scientific hypothesis, and a scientific law? A hypothesis, unlike a thoroughly tested scientific theory, is an educated guess that has not yet been fully tested or subjected to research. Hypotheses also tend to be very specific, whereas scientific theories are sweeping explanations that cover a wide range of questions about a phenomenon. The theory of evolution, for example, explains the incremental changes of all life forms on Earth over billions of years. A scientific law describes a scientific observation but doesn’t attempt to say why or how it happens, whereas a scientific theory explains exactly why or how it happens. For example, the law of gravity says that two objects will exert their gravitational pull on each other. It doesn’t say why the objects do this, however. The theory of gravity is the (much more complex) explanation as to exactly why and how these objects attract each other, encompassing all verified observations about such phenomena.

Scientific theories shape our understanding of topics in many different fields, from medicine to biology to astrophysics. A crucial aspect of scientific theories is that they can predict phenomena not yet directly observed—things that current technology can’t detect but that the theory nevertheless asserts to exist. One example of this is germ theory, developed by scientists in the 1800s. Although they lacked our current medical technology, their experiments correctly predicted the existence of viruses and bacteria. That’s more than just a good guess!

Did you know … ?

The scientific method, which is central to developing scientific theories, was formalized by 17th-century philosopher Francis Bacon, who was inspired by the many scientists who came before him and developed their own scientific theories (even if they didn’t call them that).

What are real-life examples of scientific theory?

This video breaks down the difference between a theory and a law, with some real-life examples:

What other words are related to scientific theory?

Quiz yourself!

A scientific theory is:

A. a random guess that only a handful of scientists think is true.
B. an undeniable fact of the universe that will be true forever.
C. a well-tested prediction that is accepted in some countries but rejected in others.
D. a comprehensive explanation that uses facts repeatedly proven in many experiments and is accepted by the vast majority of scientists.

How to use scientific theory in a sentence