[Editor’s Note: This is a Part 4 of a 5 part series on whether evolution should be called a “theory” or a “fact.” For the installments, see Part 1, Part 2, Part 3, Part 4, and Part 5. The full article can be found here.]

Darwinists love to bash Darwin-skeptics who call evolution “just a theory, not a fact.” The truth is that I rarely, if ever, hear people who are closely involved with the ID movement using this line to oppose evolution. The “evolution is just a theory, not a fact” phrase tends to come from the vox populi–intelligent people who studied this issue in their biology class or perhaps have read books like Darwin’s Black Box, Icons of Evolution, or Darwin on Trial, but otherwise don’t follow the issue very closely. As I discussed in Part 1, many of us who are closely involved with the ID movement actually agree with the Darwinists that the “evolution is ‘just a theory’, not a fact” line not only (in the technical sense) misuses the word theory but generally comes off as a meaningless statement. In this post I’ll offer four reasons why I think that Darwin-skeptics should not use the “evolution is just a theory, not a fact” line and answer the question, “Is it best for Darwin skeptics to call evolution ‘just a theory, not a fact’?”

Having taken over a dozen courses covering evolutionary biology at both the undergraduate and graduate levels, I’m a scientific skeptic of neo-Darwinism. But I’ve long opposed using such a rhetorical line of “evolution is just a theory, not a fact” to oppose evolution because it gets you caught up in a semantic debate over the proper definition of fact and theory, and communicates very little about the most important component of this debate–the scientific evidence. (For an early example of my writings on this topic, see my Response to the ACLU ID FAQ.) I’ll start with criticism of people on my own side of this debate by offering four reasons why I oppose using the “evolution is just a theory, not a fact” line:

1. The statement “evolution is just a theory, not a fact,” hopes to convey some kind of skepticism regarding evolution, but it fails to adequately define the term. As we learned in Part 3, no one doubts evolution when it is defined as “populations of living organisms change over time.” Evolution so-defined is an unquestionable fact. But when evolution is defined as “natural selection acting on random mutation serves as the primary driving force that built the complexity of life” or even “all species share a universal common ancestor” (collectively called “neo-Darwinian evolution”) then you’ve traipsed into more controversial definitions of evolution.

2. The “evolution is just a theory” line is simply not a good way of expressing skepticism about neo-Darwinian evolution because it assumes that a theory is something which necessarily lacks evidentiary support. As we learned in Part 1, the problem with this phrase is that the word “theory” can indeed mean a scientific idea that is well-backed by large amounts of scientific evidence.

3. When someone says “evolution is just a theory,” it sounds like the speaker cannot cite actual scientific evidence against evolution, and that the only objection the speaker can muster is based upon appealing to postmodern rhetoric which asserts that we really can’t know if anything is true. The truth is that science is capable of studying the validity of historical scientific theories such as neo-Darwinism, but the “evolution is just a theory” line makes it sound like the speaker is not interested in studying or discussing that evidence. In the debate over evolution, discussions of evidence are what matter most. As stated previously, calling something a theory doesn’t necessarily tell you about the state of the evidence. The best way to express dissent from evolution is to actually discuss its failure to explain the scientific evidence.

4. The “evolution is just a theory” line can come off as if the speaker really thinks “evolution is just a guess so I don’t have to believe it if I don’t want to.” In fact, neo-Darwinian evolution as a whole is not merely a guess, and most Darwinian scientists will provide reasons why they think it is the best explanation for the diversification of life. If you’re like me, and you think that neo-Darwinian evolution has scientific problems, then you should be able to provide reasons why you’re a skeptic beyond stating “it’s just a theory.” As noted above, the best strategy is for you to be prepared to give a few specific scientific reasons why you question Darwinian evolution.

So if we shouldn’t call evolution “just a theory, not a fact” then how should us Darwin-skeptics refer to evolution? Theory? Fact? Hypothesis? Something else? I’ll explore this question in the final installment of this series, Part 5.