On this A Moment of Science we clear up the difference between a scientific theory and a scientific law. You know, that’s something like the argument that if the theory of evolution were true, it would actually be a law. In fact, scientists get a little weary of some people saying that the fact that evolution is a theory means that modern science itself isn't convinced it really happens.
So, it seemed like it would be a good idea to go over the terminology one more time.
Well, the definition of a law is easy. It's a description--usually mathematical--of some aspect of the natural world—such as gravity. The law of gravity describes and quantifies the attraction between two objects. But the law of gravity doesn't explain what gravity is or why it might work in this way. That's because that kind of explanation falls into the realm of theory.
And the theory that explains gravity is the theory of general relativity.
According to the National Academy of Sciences, a scientific theory is a "well-substantiated explanation of some aspect of the natural world that can incorporate facts, laws, inferences, and tested hypotheses." In other words, all scientific theories are supported by evidence, and you can test them, and—most importantly—you can use them to make predictions.
So based on that definition, theories never change into laws, no matter how much evidence out there supports them. Formulating theories, in fact, is the end goal of science. So to say evolution is just a theory is actually an argument for it and not against it. You can't do any better in science than to be a theory.