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What is a Scientific Theory?


“Theory” is one of those scientific words that often gets used in non-scientific situations. For example, if you see the same two birds returning to a tree by your house day after day you might say, “I have a theory that there’s a bird’s nest in that tree”. When used this way, “theory” means a hunch or a guess.


However, when scientists use the word “theory” they’re not talking about a hunch or even an educated guess. A scientific theory is a broad, well-supported explanation about how something in the natural world works. Some well-known scientific theories include Darwin’s Theory of Evolution, to explain how species change and adapt over time, and Einstein’s Theory of General Relativity, to explain the force of





This is symbolic. Not how human evolution progressed.

(Clker-Free-Vector-Images, 2014)


Scientific theories are similar to hypotheses in some ways, because they both seek to provide a potential explanation for natural phenomena. The difference is that hypotheses have a much smaller scope and are meant to be tested and potentially rejected. For example, a hypothesis might explain why an apple falls towards the ground when you drop it, while a theory would explain how gravity works as a whole, from falling apples to the movements of planets.


Theories may, however, be supported by well-confirmed hypotheses as well as facts and laws. Facts are objective, measurable observations that are explained by a theory. For example, the observation that an apple fell when you dropped it from your hand would be a fact.


A scientific law is a description of observed scientific facts. In our apple example, a law might describe with precise mathematical equations how fast objects fall towards the earth when dropped. The important difference between a law and a theory is that a law only describes how things occur, not why they occur. That’s the difference between Newton’s Law of Universal Gravitation and Einstein’s Theory of General Relativity.


Theories are a vital part of the scientific process, because they allow us to bring all our observations and studies about a part of the natural world into one cohesive explanation. Darwin’s Theory of Evolution has helped scientists better understand just about every subject in biology, from animal behavior to genetics.  


Just like everything in science, even scientific theories are not set in stone. While it’s extremely rare for well-established theories to be outright disproven, most theories are built-upon and adjusted as we gain a better understanding of the subject at hand. To return to the example of the Theory of Evolution, Darwin didn’t have access to the cutting-edge genetic technology we have nowadays. Discoveries in genetics have updated our understanding of evolution, which has helped improve upon Darwin’s initial theory.


Image Citation:


Clker-Free-Vector-Images. (artist). (2014). Evolution Walking Charles Darwin [digital art]. Retrieved from

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