This fallacy occurs when a writer argues that, because we don't know something is not true, it must, then, be true. According to The Well-Crafted Argument, "The basis of the appeal here is that we can decide based on what is not known. [. . .] One often encounters appeals to ignorance in informal scientific speculation. Have you ever gotten into a conversation about the likelihood of intelligent life on other worlds? You might commonly hear a line of reasoning that goes something like this:
True, we haven't the slightest blip of evidence that intelligent beings exist beyond earth; but the universe is so vast and our understanding of what the universe could contain is so meager that there must be intelligent life out there somewhere!" (157)
In the absence of direct evidence of life beyond earth, we can't conclude that life exists.
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