Moving the goalposts is a fallacy in which the two parties in a debate agree on evidence that would refute a claim, but then, when such evidence is presented, the “losing” side insists that the given evidence is insufficient. At first, this might not seem like a fallacy, because while it is obviously a cheap shot to use in a debate, the logical implications of it are not so obvious. But as we will see, it is, in fact, a logical fallacy.
An example of moving the goalpost can be found when discussing the topic of evolution, as in this example argument:
Bob: If evolution is real, then show me an example of evolution occurring right now.
Suzy: Sure. Just look at the rise of antibiotic-resistant bacteria. As antibiotics are used, they apply selective pressure that weeds out those that are susceptible to it, allowing those that are resistant to grow out of control.
Bob: No, that doesn’t count. Show me an example that occurs over long periods.
In this debate, Bob is guilty of moving the goalpost. First, he suggests that an example of evolution occurring right now would make him change his position. But then, when such evidence is given, he changes his definition of evolution to exclude species changes that occur over short periods, effectively making it impossible to refute his claim. How can you possibly provide evidence of evolution…
