‘It’s only a theory’

by Tim Harding, B.Sc., B.A.

(An edited version of this article was published in The Skeptic magazine,
June 2018, Vol 38 No 2)

One of the most face-palming things about having a science background is when creationists or other science deniers say ‘It’s only a theory’ when dismissing a scientific theory such as evolution.  This was recently the misconception that frustrated readers the most on The New York Times – Science Facebook page.

In everyday conversation, we tend to use the word ‘theory’ to mean a hunch, a guess or tentative hypothesis, as opposed to a known fact.  But that’s not what a ‘theory’ means to scientists.

‘In science, the word theory isn’t applied lightly,’ says Kenneth R. Miller, a cell biologist at Brown University. ‘It doesn’t mean a hunch or a guess. A theory is a system of explanations that ties together a whole bunch of facts. It not only explains those facts, but predicts what you ought to find from other observations and experiments.’

Photo credit: Zohar Lazar

The word ‘proof’ is used in mathematics but not in professional science.  I don’t recall ever seeing the word ‘proof’ used in this sense in a published scientific paper.

The prevailing scientific theory is the one that best explains the facts and has not been falsified, despite experimental attempts to do so. As Richard Dawkins says ‘Gravity is a fact. Evolution is a fact. The prevailing theory of gravity is Einstein’s. The prevailing theory of evolution is Darwin’s.’  Dawkins has also invited anyone who doubts the theory of gravity to test it by jumping out of a tenth-storey window.

This conflation of two different meanings of the word ‘theory’ is an instance of the equivocation fallacy.  In logic, equivocation is an informal fallacy resulting from the use of a particular word or expression in more than one sense throughout an argument, leading to a misconception.  It is a type of ambiguity that stems from a term having two distinct meanings, not from the grammar or structure of the sentence.

Reference:

Zimmer, Carl. In Science, It’s Never ‘Just a Theory’. The New York Times, April 8, 2016.