Kyle Polk, Brittany Ferguson, Yu Jin Henson

 an informal logical fallacy in which previously agreed upon standards for deciding an argument are arbitrarily changed once they have been met. This is usually done by the "losing" side of an argument in a desperate bid to save face. If the goalposts are moved far enough, then the standards can eventually evolve into something that cannot be met no matter what.

RationalWiki.org

(our Definition)

Creation vs. Evolution Example:

Antagonist: "Evolution is clearly impossible; no life form can change"Protagonist: "Um, livestock breeders do it all the time. Where do you think hybrid roses come from?"Antagonist: "Well, that's just microevolution. You breed a new rose, it's still a rose. What you can't do is breed a new species."Protagonist: "Actually, we can and have. There's lots of examples of observed speciation.Antagonist: "Yes, but you still just get another variation of the same kind; you never get a completely new type of animal. You can't breed a dog and get a chicken."

The key to understand this fallacy is to understand what a claim under discussion actually means. In most cases, the actual "claim" is a relatively broad and perhaps ill-defined one. In most cases, the person making such a claim will have an intuitive, informal idea of what he really means, but cannot necessarily articulate the exact evidence upon which he bases his idea. Some concepts are hard to articulate and even harder to demonstrate, but it may nevertheless be real.

On the other hand, "moving the goalposts" can also be a sign that the claimant has made up his mind and is impervious to evidence. If he is convinced, for example, that a pattern exists, any single counterexample can be dismissed as unrepresentative.

Hoax “The Apollo Moon Hoax: Why Haven’t Any Pictures Been Taken of the Landing Sites?” “If Apollo really landed on the moon, then why haven’t we taken pictures of it?” However, scientists, skeptics, and even many in the general public have maintained

that it was simply a matter of time before we had a space craft in orbit of the moon that actually would have a high enough resolution camera to take photographs of the Apollo landing sites and show the relics. NASA’s Lunar Reconnaissance Orbiter, which went into orbit this year (2009), was just such a craft and over the summer, NASA released photographs of several of the landing sites, showing the relics.

Now, logically, that case would be closed. The hoax claim was answered originally, and it was now even answered “better” with real photographs showing just what they said wouldn’t exist.

However, the Moving the Goalpost fallacy struck again and what many of us said would happen did: The hoax proponents who have actually spoken on these photographs have simply claimed that NASA has faked (“Photoshopped”) them. The goalpost hath been moved.

Non-Astronomy Example of Moving the Goalpost from Vaccines Give You Autism Crowds

Very very rarely have I strayed away from astronomy topics and claims on this blog, but this example of Moving the Goalpost was simply too good to pass up. For many years throughout the 1990s, a group of people claimed that the thimerosal mercury-based preservative in vaccines caused children to have autism. They lobbied hard for the preservative to be removed from all childhood vaccines, claiming that that would eliminate or greatly reduce apparently rising rates of childhood autism.

They made a VERY testable claim and prediction. And by about 2003, thimerosal was removed from all childhood vaccinations, at least in the US.

Again, logically, one would think that the claim had been disproven. Their cause, thimerosal, had been removed, so their claimed effect, autism, should be greatly reduced. Autism rates continued to be the same, not even a statistical blip due to the removal of thimerosal. Yet the anti-vaccination movement persists today, still claiming that vaccines give children autism, though now they will usually claim it’s due to diverse “toxins” in the vaccines. And still, some will claim that it’s the thimerosal in the vaccines … a case which now is simply a lie. Again, they have shifted the goalpost, not acknowledging they were wrong about thimerosal, but moving on to some other claim.