Easily (and sadly) one of the more common claims amongst the… err.. “less intellectual” of the anti-evolutionist crowd, “It’s just a theory!” is roughly analogous, at least from my perspective, to “I don’t understand science, therefore Evolution is false!” or if I’m feeling less generous “Call me a moron again, I like it!”
For those looking for a simple, fast response to this claim: “So is [insert germ theory/atomic theory/the theory of gravity and/or the theory of general relativity]” suffices. Depending on the tone used, this simple statement can be expressed as anything from polite confusion (“But, hang on, isn’t gravity “just a theory” as well?”) to pure, scornful, unadulterated sarcasm (“By god, you’re right! What have we been doing teaching germ theory to the poor innocent children all this time? Teach the controversy!”).
For a more complex answer, you have to realise the common misconception this claim stems from: that “theory” in science means the same thing as it does in general usage. In general usage, “theory” can refer to anything from “If I keep working this hard I might just get a pay raise” (false) to “maybe if I show that person my gigantic genitals they’ll sleep with me” (false) to “I bet I can grow an aquatic super-soldier clone army by combining cuttlefish DNA with human DNA” (true). In scientific usage, it is just a wee bit different.
Many people believe that an idea starts as a “theory”, gathers evidence to become a “fact”, and finally gets proven to become a “law”. This flawed idea also explains a variant of the “it’s just a theory” argument, where the user claims they support teaching evolution, but not “as fact”. It is also part of the reason things like the Laws of Thermodynamics are so treasured by certain subgroups of evolution-denialism: they are seen as the immutable truths of science, the pillars on which the Lab Coat Of Knowledge sits, all shiny-white and glowing.
Back in reality, really real realistic scientists would stare at the above diagram with the expression of one trying valiantly to fathom just how anyone could possibly believe that. And then they’d laugh hysterically at your ignorance. Unless they were polite scientists (through selective breeding and various indoctrination techniques we finally managed to produce one of these. Unfortunately, attempts to introduce it into the wild populations were… unsuccessful. And messy).
Fact: A fact is an observation, a data point, something we can point to and say “that happens”. That things fall at a rate of 9.80665 m/s on earth is a fact. A fact never changes: it is an aspect of reality that must be accounted for. No matter how much we refine and change the theory of Gravity, it will remain true that things fall at a rate of 9.80665 m/s on the surface of the earth.
Law: A law is a mathematical representation of a physical phenomena. That things are subjected to the force of gravity at a rate of of Gm1m2/r2 is a law. A law, contrary to the above misconception of science, can change when our measurement tools get better and we discover that the law is only mostly correct. This is what happened to Newton’s laws (like the one above), and we’re now seeing it happen to Einstein’s laws.
A fact does not become a law: they are two entirely separate creatures. Laws can be derived from and supported by a number of facts, however.
Theory: A scientific theory is something far bigger and more important than either of these: it’s an explanation that ties together dozens, if not hundreds or even thousands of facts and more than a few laws as well. A theory grows in detail and scope as facts are added to it over time, and its strength is in them: new facts can change the specifics of the theory, but it takes something radical and contradictory to overthrow it entirely. And to make it even harder for the incoming theory, it has to provide an explanation for everything the old theory did.
If you want the scientific term for a drunken guess, that would be “hypothesis” (though, in all fairness, not all hypothesis’ are drunken guesses). Evolution has not been a hypothesis since Charles Darwin was first realising it: by the time he released Origin of Species it was a fully-fledged Theory, and it has only gotten stronger in the 150 years since then, thanks at least in part to the untiring efforts of its detractors attempting and failing to disprove it.
For the record there isn’t a warlike civilisation of cepholopod-men off the coast of Florida and it wasn’t us who put them there.
PS: We’re still having technical difficulties of the “computer == x_X” variety, so todays illustrations are brought to you by letter’s “F” and “U”.