Fallacy?

Argument from incredulity

“I can't imagine how this could happen, so it didn't.”

Also called: Personal incredulity

The test

Is there a calculation, a measurement or an experiment behind the doubt, or only a failure of imagination?

Richard Dawkins named this fallacy in The Blind Watchmaker as a charge against critics of evolution, and it is a fair charge against some of them. Imagination is a poor guide to what is possible.

But the same move appears on the other side, whenever a design is dismissed because its purpose is hard to imagine. And there is an important difference between incredulity and a calculation. An argument that the required mutations would take longer than the time available is not incredulity. It can be checked, and should be.

Seen on both sides

In mainstream arguments
It would argue from incredulity to say: I cannot imagine why a designer would make something this way, so it was not designed.
In critical arguments
It would argue from incredulity to say: I cannot see how an eye could ever evolve, so it did not.
Not a fallacy when

The doubt rests on a quantitative argument, about rates, probabilities or waiting times, that can itself be checked.

Diagnosed on this site

Not yet diagnosed in any pillar or claim card.

Further reading

  1. Dawkins R. The Blind Watchmaker. Longman (1986), which names the “argument from personal incredulity.”