What are the two forms of the appeal to ignorance fallacy?

The appeal to ignorance fallacy can take two forms:

  • Arguing that a claim is true because it has not been proven false (e.g., “Ghosts are real because science has never disproved their existence.”)
  • Arguing that a claim is false because it has not been proven true (e.g., “We’ve found no clear evidence of life on other planets, so that proves we’re alone in the universe.”)

Both forms of the fallacy make the same essential error, misconstruing the absence of contrary evidence as definitive proof.