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What does the word “theory” imply to you? That answer might vary depending on your familiarity with science. In other words, when you hear someone try to dismiss or denigrate an aspect of science by saying “it’s just a theory,” keep in mind that in the language of science a “theory” is actually a pretty solid proposition.

I was spurred to this line of thought by newly published book from the National Science Teachers Association, Evolution in Perspective, by Rodger Bybee. The book’s premise is that, “only those students whose schools teach them about the nature of science will truly understand evolution.”

Evolution is still derided by some critics as a “mere theory,” usually in order to have this subject presented in an uncertain fashion (or not at all) in classrooms. However, this is a classic case where a choice of word can seriously undermine an argument.

If you’re discussing a scientific theory, then the scientific definition of the word “theory” probably should take precedence over more common usages of the term. Here’s how one science dictionary defines theory:

“In science, an explanation for some phenomenon which is based on observation, experimentation, and reasoning. In popular use, a theory is often assumed to imply mere speculation, but in science, something is not called a theory until it has been confirmed over the course of many independent experiments. Theories are more certain than hypotheses, but less certain than laws.”
— BioTech Life Sciences Dictionary,(Indiana Inst. for Molecular and Cellular Biology)

It’s easy to see how the confusion over “theory” arises. Here are two out for the six definitions that the American Heritage Dictionary lists for that word:

“…A set of statements or principles devised to explain a group of facts or phenomena, especially one that has been repeatedly tested or is widely accepted and can be used to make predictions about natural phenomena.”

“…An assumption based on limited information or knowledge; a conjecture.”

Clearly, those two terms imply very different levels of certainty or credibility for a “theory” – but just as clearly, the first definition is far more applicable to a discussion of science than the second.

Here’s a great educational tool I found to explain what “theory” really means in the context of science. See this Dialogue on Teaching about the Nature of Science, from the National Academies Press. (You’ll have to scroll all the way down to the bottom of a long page to get to it.)

Why am I harping on varying shades of definitions? Because this is one clear case in which an ambiguous word choice is used as a strategy to influence policy. Rather than simply accept that words are being used appropriately and accurately in a situation where opinions are strong and the stakes are high, take a moment to peek at a dictionary. It’s a valuable reality-check.

The responsibility to use key words correctly works both ways. The NSTA book points out that science educators also have a responsibility to use the word “theory” with care. In the essay “It’s not Just a Theory,” Bybee writes:

“…as is the case with most effective, inquiry-based instruction, we should not just tell students about nuances related to the nature of science, but rather practice careful use of the language… Educators should not ask, ‘What is your theory concerning,’ but rather, ‘What is your opinion concerning,’ or, ‘What are your thoughts concerning?’”

Excellent point.