Therefore, consider this post Science Terminology 101: a brief look at terms that people don't get.
Fact: A fact is something that exists, that is reality. In science one may think of a fact as something that is observed. It does not explain anything, it is just a simple truth.
Law: A Law describes a discreet event or action or fact. And that is all it does. Generally, a law can be summarized in a mathematical formula such as the law of gravity:
A law does not explain anything about the event or action, but simply describes what happens. If you drop a stone or a ball or a baby, it accelerates toward the center of the Earth in this way (the law actually says more, and is not limited to things on earth falling, but you get the point). It says nothing about why this happens (to be fair, there is also a Theory of gravity which does explain the why, but let's not confuse the issue here), merely that it does, every time. A thousand or a million or a billion trials will never find something suddenly fall "up" into the sky..
Hypothesis: A hypothesis is a prediction based on prior knowledge. It is not a random guess, but a predicted outcome given what is known about the phenomenon and/or related principals. For example: If I were in the lab, and was about to add a beaker of liquid to a water sample with living algae I could guess that it would make the algae bloom, or die, or turn pink, or sprout wings and turn into butterflies for that matter (though I admit that's a bit of a stretch). However, because I know that the sample of liquid is chlorine bleach, and I know from other lab work and practical experience it's properties, I can make a prediction about the outcome, which is now a hypothesis because I have reason to think this will be the outcome. If a different outcome occurs, then I can discard or modify my hypothesis and have increased my background knowledge about the phenomenon in the process.
Theory: Now we get down to the meat of this post, and the source of so much confusion. It may be helpful to begin by pointing out what a scientific theory is not: A scientific theory is not the same as a "theory" as we use the term colloquially. It is not an opinion or a guess or someone's fanciful idea. A theory generally can't be summarized as a mathematical equation like a law, and indeed, it is not a fact, nor is it a law, and, it will NEVER be either of those things. That is one of the common misunderstandings of the terminology: many think that after sufficient scrutiny, a theory becomes a law, and this is not the case. A theory and a law do not lie on a continuum of certainty. They are different animals altogether. Again, a law simply describes something that happens, and has absolutely no explanatory power, where a theory is an explanation based on many facts, and often several laws. A theory has been tested many times, and is supported by the results of experimentation, and has not been disproven.
Since a theory attempts to explain the "why", it can't be a fact or a law. But make no mistake, when it comes to scientifically explaining why things are the way they are in the natural world, the Theory is the master of the realm.
Speaking specifically on the Theory of Evolution: this theory having been tested so many times, having made so many (correct) predictions, and having mountains of evidence is one of the best supported theories in any science. A huge part of our breakthroughs in medicine, genetics, agriculture, etc. can be attributed to the strength of this Theory. When someone tries to convince you that the Theory of Evolution will be crumbled by some little tidbit of information that they have come up with (but thousands of scientists spanning nearly two hundred years have not thought of), you can bet they are very ignorant, or are trying to mislead you.
It should also be noted, that we have observed evolution take place, and in this way, evolution is also a fact. We have watched it happen (see the definition of Fact above). So when someone says "evolution is just a theory, not a fact", they are being deceptive with half the statement, and wrong about the other.
"Just" a theory? Yeah, a theory it is, and one of the most well supported scientific principles and a keystone of Biology. It's time to drop the tag, or recognize that when someone uses it, they are not conveying the true weight of what a scientific theory is.
