In the great evolution wars, I've noticed something get trampled on, misinterpreted, dragged around unceremoniously, and fall to the wayside: The concept of a scientific law. It's almost as if it falls into a nebulous gray area of whatever we want it to be to prove our point. People, generally the more ignorant side of the anti-evolution crowd, will say over and over again, "It's just a theory and not a law." Seemingly unaware that a theory is recognized among scientists to be a very good and evidence-based explanation of a set of phenomena. They use the word theory the way most people do in conversation, to mean "guess". This is something the more educated (but still wrong) anti-evolution people recognize and the honest among them do not perpetuate the argument. Still, they and even the people in the pro-evolution crowd seem to not consistently use the word law to mean what it actually means.
There are two issues at the heart of this. The first is the way common language differs from the way scientists will talk. I told a friend about a simple solution I came up with to a problem I was having, I said I had a hypothesis which I confirmed. He turned to me and sarcastically asked, "Oh really, you had a hypothesis about [trivial problem I can't remember]?" He said this as if I did some grandiose experimentation and analysis. He seemed to argue by implication that a hypothesis is a big thing. Whereas if I had used the word "theory" he wouldn't have objected, that's just how people talk. The word law is subjected to this same abuse, since it seems to imply a definite certainty. In fact, while more informed people know what a hypothesis and a theory is, use of the word "law" isn't really considered carefully.
The other issue is that science has no governing body. There are organizations like IUPAC and the AAS and even the AAAS that attempt in their own big and small ways to bring scientists onto the same page. But certain ideas and concepts aren't always codified, mainly because scientists can do their work well enough without having to sit down and hash out, "Hey, what is a law anyway?" What exactly a law happens to be doesn't impact how scientists work, but is more important as a concept in the philosophy of science.
First, I want to make some things clear, since there are two common misconceptions contributed to in part by, of all things, textbooks. Textbooks will often show the relationship between a law and a theory graphically, which necessitates drawing an arrow from a law or group of laws to a theory. This leads to the idea that:
A) Theories are laws that have been confirmed.
B.)Theories are a set of laws.
Neither of these are true. A law, is in fact a simple observational model of how the world works, minus any explanation. It is, at its core- how the world works, as opposed to why. So a law is often condensed into a simple mathematical statement like:
These are descriptions of how the natural world seems to work. The first is an equation that defines force, relating it to mass and acceleration. The second is the ideal gas equation that describes the relationship between the pressure, volume, amount, and temperature of an ideal gas using a constant called R. These are immutable facts about the world around us as confirmed by experiment. They are basic models. You might call them equations, but when you discover how these equations can be rearranged and manipulated, you discover that they are in fact- capable of modeling a range of behaviors.
Notice that there is nothing in them that shows how they work. In the force equation, we know that increasing the acceleration of an object increases the force it exerts. From the ideal gas equation we know that lowering the temperature of a gas lowers the volume. But we don't know why the volume changes or the force increases from the equations. We simply know that they do. It's only when we have a theory, something that looks at the various laws and offers some explanation of why they seem to work that we understand the underlying mechanism.
The kinetic theory offers us a cohesive explanation of the ideal gas law. Because the explanation is so general, it offers us an explanation of other things as well, like the Arrenhius equation. It's a bigger model that shows us why the various laws seem to work. Why is force dependent on mass and acceleration? We had to wait for Einstein to really begin to understand that, and quantum electrodynamic theory to start to home in on anything resembling a satisfying answer.
So to go back to evolution: There was never a law of evolution, and the theory of evolution is not some textbook of smaller laws and principles. Instead the theory of evolution explains why a set of smaller models and laws work. It answers the why for instance, of the Hardy-Weinberg equation, it doesn't contain the Hardy-Weinberg equation like a big box.
Laws and theories are only dependent on each other to the extent that they are logically consistent. A good theory, one used by scientists to develop new laws, has proven itself so consistent with other laws and within itself as a framework that new laws and behaviors can be predicted. So evolution already existed as a theory before Hardy-Weinberg was created as a law that showed evolution happening in the natural world. Other times, laws can be pulled together to see whether a theory makes sense. Laws like the ideal gas equation and Arrenhius's equation along with many others have proven conclusively that the phlogiston theory of chemistry could not be true as long as these laws remain valid.
So when a law is in it's infancy, it's appropriate to refer to it as a hypothesis or series of hypotheses. When a theory is in its infancy, it's appropriate to refer to it as a conjecture, or a series of conjectures. Just don't balk when a scientist says hypothesis to mean theory, and conjecture to mean hypothesis. Remember what I said earlier, scientists know what they're talking amongst themselves, so they tend to neglect that the rest of us will be left in the lurch.
So what's the test an average person can use to decide for themselves? Ask for evidence. When a small specific general rule is discovered, and it's confirmed with evidence that it works, it's a law, or part of a law. When a grand explanation isn't contradicted or not at least generally explained by the evidence and the various laws and observations, it's a conjecture.
Evolution is a theory because the laws of genetics, molecular chemistry, mathematics, and statistics underpinning it have been shown to predict behavior in the real world. Within itself, the model evolution posits is largely self-consistent with the evidence so far.
So now I hope the next time you look at a textbook and see arrows and flowcharts demonstrating the process of science, you'll have a better idea of how it really works.