If it walks like a duck, quacks like a duck, and repositions its habitat 135 miles north like a British comma butterfly, it must be…global warming. Or one datum, anyway, in a convincing body of evidence for rising temperature and climate change. No one knows precisely how much of this trend results from human activity (burning of fossil fuels, production of excessive political hot air, etc.) but it’s a significant factor, according to the present scientific consensus.

But, ah, “scientific consensus” – there’s the rub.  We are all victims of an unfortunate problem of terminology, which plays into an essential misunderstanding of how science works.

One part of the problem is a misperception of what “scientific consensus” implies, but I’m concerned here with something more basic: the word “theory.” From a Greek term meaning viewing or contemplation, with a shading of “speculation,” the word came to mean, in the lexicon of modern science, “A scheme or system of ideas or statements held as an explanation or account of a group of facts or phenomena; a hypothesis that has been confirmed or established by observation or experiment, and is propounded or accepted as accounting for the known facts; a statement of what are held to be the general laws, principles, or causes of something known or observed” (Oxford English Dictionary). A theory, in short, is a former hypothesis that’s all grown up, no longer just suggested or proposed. Thus we have the theory (not the hypothesis) of evolution. There isn’t just overwhelming geological and molecular evidence for evolution; we can also see it happen.

In popular use, though, we often use “theory” as a synonym for “hypothesis.”

– “Why is she such a bitch?”

– “Because she’s an only child – that’s my theory.”

This results in a misunderstanding about science: that science produces ideas but can never fully prove them, and that therefore these ideas are like social or religious views, always subject to personal bias or faith – eternally debatable matters of opinion.

Many who aspire to high office apparently share this misunderstanding. (I say “apparently” because, almost by definition, you can’t take anything a politician of any stripe says as necessarily representing his or her actual beliefs.) Texas Governor Rick Perry said the other day that “the issue of global warming has been politicized” (as if he weren’t taking part in that happy process!), and expresses the absurd opinion that “there are a substantial number of scientists who have manipulated data so that they will have dollars rolling into their projects…almost weekly, or even daily, scientists are coming forward and questioning the original idea that man-made global warming is what is causing the climate to change.” He added, “I don’t think…that I want America to be engaged in spending that much money [billions or even trillions] on still a scientific theory that has not been proven.”

There are those pesky words again – “theory,” “proven.”

A bit lower down the evolutionary ladder (I know, evolution isn’t a ladder, it’s a bush, but I couldn’t resist the metaphor) is Republican candidate for U.S. Senate Kevin Coughlin of Ohio, whose mangling of the facts reached epic levels last week when he was asked about global warming. Calling the science behind it “sketchy,” he expanded on his – let’s call it a hypothesis – thus: “There is no question that the earth’s core is increasing slightly in temperature, but…I don’t really think there’s much evidence to suggest that people have or can do much to change anything.”

So now it’s the earth’s core that’s warming. (Maybe we need Bruce Willis again.) How are greenhouse gases managing to get all the way down there? Could it be those frakking chemicals? Now there’s a theory. I’d best get to work hypothesizing it. After all, if scientific theories are just opinions, and everyone’s entitled to their opinion, then I’m a scientist…and so are you!