The Difference Between A Fact, Hypothesis, Theory, And Law In Science

Words such as “fact”, “theory” and “law” get thrown around a lot. When it comes to science, however, they mean something very specific; and knowing the difference between them can help you better understand the world of science as a whole.

In this fantastic video from the It’s OK To Be Smart YouTube channel, host Joe Hanson clears up some of the confusion surrounding four very important scientific terms: fact, hypothesis, theory, and law. Knowing the difference between these words is the key to understanding news, studies and any other information that comes from the scientific community. Here are the main takeaways:

  • Fact: Observations about the world around us. Example: “It’s bright outside.”
  • Hypothesis: A proposed explanation for a phenomenon made as a starting point for further investigation. Example: “It’s bright outside because the sun is probably out.”
  • Theory: A well-substantiated explanation acquired through the scientific method and repeatedly tested and confirmed through observation and experimentation. Example: “When the sun is out, it tends to make it bright outside.”
  • Law: A statement based on repeated experimental observations that describes some phenomenon of nature. Proof that something happens and how it happens, but not why it happens. Example: Newton’s Law of Universal Gravitation.

Essentially, this is how all science works. You probably knew some of this, or remember bits and pieces of it from grade school, but this video does a great job of explaining the entire process. When you know how something actually works, it makes it a lot easier to understand and scrutinize.

Theory vs. Hypothesis vs. Law… Explained! [YouTube]


  • It always cracked me up when some school district in the U.S., at the behest of the local religious fanatics, put warning stickers on science textbooks informing the students that ‘evolution was just a theory’.

    • the bible needs to be labelled with the 5th tag: Fact+Theory+ Hypothesis+ Law+Fable.
      anyway, i’m a little bemused by evolution itself: how can we really know that evolution occurred when we did not witness it ourselves? i mean it’s all good to say that one fossil has similarities to another and hence it must of preceded/succeeded it in evolution, but we can never be certain because we didn’t witness it (nor will we ever be able to). this is all fancifully, scientifically packaged conjecture.

      • You can google “How can we be sure of evolution if we didn’t witness it first hand” or something along those lines and you’ll have that question, and any other you might have, addressed.

        Because you can’t be bothered doesn’t make evolutionary theory ‘fanciful conjecture’.

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