Who gets to define "theory"?

Our colleague, Mike Klymkowsky of the University of Colorado, the other day posted an interesting article, Ideas are cheap, theories are hard, in the Plos blog Sci-Ed. In the article, Professor Klymkowsky inveighed against the public’s supposed misuse of the term theory.

Merriam-Webster (according to my antique, 1993 Collegiate Dictionary, 10th edition) lists senses (meanings) of the word in approximately chronological order. It gives the earliest sense of theory as “a plausible or scientifically acceptable general principle or body of principles offered to explain phenomena.” This definition dates from the 1600’s. The word later came to mean “a hypothesis assumed for the sake of argument or investigation,” or “an unproven assumption,” or a conjecture. There are other senses which we need not go into. The online version of Merriam-Webster, incidentally, includes 2 short articles, “The difference between hypothesis and theory” and “Two related, yet distinct, meanings of theory.” They note, in particular, that in nonscientific use, hypothesis and theory may be used interchangeably with “idea, speculation, or hunch.”

Professor Klymkowsky objects to the use of theory to mean hypothesis or hunch because it allows creationists or others to say that the theory of evolution is only a theory, using theory in the colloquial sense of idea or hunch. Merriam-Webster makes the same point, though they do not proscribe using theory to mean hypothesis.

Theory is a term of art in science. Professor Klymkowsky’s essay explains clearly what it means and why theories are hard to come by; it is well worth reading for those reasons alone. I used to tell my senior-design class that a theory was a “well evidenced exposition of a natural phenomenon.” In physics, though, I think it means “a mathematical description of a natural phenomenon.”

It is hard for me to be a permissivist, and I do not quite agree with Humpty Dumpty when he said – scornfully – that a word means what he chooses it to mean. Rather, a word means what it means depending on context. In the layperson’s context, a theory is a hunch or speculation. If you applied the physics definition – a mathematical description – to biology, then the theory of evolution as enunciated by Darwin and Wallace would not be considered a theory, because it was nonmathematical.

In physics, we usually use force to mean the change of momentum with time (though electromotive force, we must admit, is in fact not a force). That is different from calling my mother-in-law a force of nature. It is even more different from what Dylan Thomas meant when he said, “The force that through the green fuse drives the flower/Drives my green age….” None of those sentences is wrong, though each uses force very differently.

When a layperson says, colloquially, that evolution is only a theory, that person is committing a category error: using the wrong sense of theory. Instead of trying to get people to drop the colloquial sense, we need to explain that a theory means something different in science. We would have to explain that anyway, so I think we might as well stop trying to do away with the colloquial sense, an activity that Professor Klymkowsky himself called quixotic.

Back to my question, “Who gets to define theory?” Context. The next time someone tells you that evolution is only a theory, simply explain that theory in science is a term of art and does not mean hunch, bunch of unproven ideas, or even hypothesis. Rather, to call something a theory is high praise, because a theory is a body of observation and interpretation, and a mature, well evidenced theory should be considered to be “true” beyond a reasonable doubt.