Scientific Theory vs Scientific Law

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Today’s post is part of a special series here on Planet Pailly called Sciency Words.  Every Friday, I bring you a new and interesting scientific word to help us all expand our scientific vocabularies.  Today, I want to do something a little different and take a look at two terms that we all probably know but are too often misunderstood.


You may hear someone say, “Well, evolution is just a theory,” as though that means it’s a trivial thing, little more than guesswork.  A common misconception is that, if we really knew for sure, if there truly were no doubts, we’d call it a scientific law.  So since there is no “Law of Evolution,” that must mean the matter is still suspect.  Perhaps the whole evolution idea may one day turn out to be wrong.

I was taught in school that there are three levels of scientific certainty.  First comes the hypothesis, an untested idea based on scientific observations alone.  Next comes the theory, a hypothesis that has survived all the experiments we’ve tried thus far but is still “just a theory.”  Lastly, we have scientific laws, which are theories that have been proven beyond all possible doubt, that cannot be challenged or overturned, that are absolute, scientific Facts (with a capital F).

That’s a convenient hierarchy, one that was easy for my twelve-year-old self to understand, but it’s not actually the way things work.  There are several different definitions for scientific theories and scientific laws.  The distinction sometimes involves whether or not the theory/law uses mathematics.  Sometimes it’s a question of whether or not the theory/law describes some specific phenomenon or a more generalized view of nature.  And some experts will tell you there is no difference between them whatsoever.

The view I have come to accept is that the difference has more to do with the fashion of the time than anything else.  In the 17th and 18th Centuries, scientists generally called their discoveries laws (for example, Newton’s Law of Gravity or Kepler’s Laws of Planetary Motion).  Scientists in more modern times, such as Darwin (19th Century) or Einstein (20th Century), prefer to call their discoveries theories.  This may reflect a changing attitude among scientists who had come to realize that nothing in science is ever 100% certain.

So what happens when a law or theory is “disproven,” and what would happen if a new discovery seriously challenged the Theory of Evolution?  Well, when Einstein’s Theory of Relativity “disproved” Newton’s Law of Gravity, that did not mean that gravity suddenly went away.  We still use Newton’s law today because it’s a close approximation of the truth, at least until you approach a black hole or try accelerating to the speed of light.  Under those conditions, Newton can’t help you, mainly because he had no idea such things were even possible.

One day, we may learn that Darwin’s Theory of Evolution is only an approximation of the truth.  In fact, that’s already happened thanks in part to the discovery of DNA, something that Darwin didn’t know existed.  The result was not the end of evolution but the development of a new, more sophisticated theory, one that adds greater precision and detail to its predecessor.  We might call this the Theory of Genetic Evolution in order to distinguish it from Darwin’s original idea, but the basic concept remains the intact.

In science, nothing is proven beyond all possible doubt, but that doesn’t mean new theories completely replace the old ones.  One theory builds upon another and upon another.  Einstein built upon the work of Newton, Newton upon the work of Galileo, and so forth all the way back to the natural philosophers of Ancient Greece.  Science continuously makes new discoveries and refines its understanding of nature.  Whether we call these discoveries theories or laws doesn’t matter.  What matters is that science keeps evolving.

P.S.: Special thanks to Mark Ball for suggesting scientific theory as the subject for today’s post.  Please check out Mark’s website, Sci-Fi Ideas.  It’s a great place for both science fiction fans and science enthusiasts to muse over the many possibilities of our universe.

P.P.S.: The great science fiction writer Isaac Asimov once wrote an essay entitled “The Relativity of Wrong.”  Click here to read it.  It’s one of my favorite pieces on science, and it was a real eye-opener for me back when I still believed in that silly hierarchy of scientific certainty I’d learned in school.

7 thoughts on “Scientific Theory vs Scientific Law

  1. I actually remember learning those three levels, but I think this is the first time I actually learned anything. Thanks once again James for an informative, educational, and interesting topic.


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